Los Angeles Survival Habits Of The Soul

When in the wilderness in Los Angeles , the most important thing to remember is that nature is not always a kind, gentle mother. The morning can be warm and sunshiny with not a cloud in the sky. But that doesn’t mean that by early afternoon, conditions won’t have changed dramatically.

Survival Axe Elite Multi Tool In Los Angeles

Survival Belt Buckle With Fire Starter And Knife

Survival training is important for astronauts, as a launch abort or misguided reentry could potentially land them in a remote wilderness area. Survival skills in Los Angeles are techniques that a person may use in order to sustain life in any type of natural environment or built environment. These techniques are meant to provide basic necessities for human life which include water, food, and shelter. The skills also support proper knowledge and interactions with animals and plants to promote the sustaining of life over a period of time.

Cabbage

What To Put In A Survival Emergency Kit This is the latest accepted revision, reviewed on 16 August 2018. Jump to navigation Jump to search Herbert Spencer coined the phrase "survival of the fittest". "Survival of the fittest" is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. In Darwinian terms the phrase is best understood as "Survival of the form that will leave the most copies of itself in successive generations." Herbert Spencer first used the phrase, after reading Charles Darwin's On the Origin of Species, in his Principles of Biology (1864), in which he drew parallels between his own economic theories and Darwin's biological ones: "This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection', or the preservation of favoured races in the struggle for life."[1] Darwin responded positively to Alfred Russel Wallace's suggestion of using Spencer's new phrase "survival of the fittest" as an alternative to "natural selection", and adopted the phrase in The Variation of Animals and Plants under Domestication published in 1868.[1][2] In On the Origin of Species, he introduced the phrase in the fifth edition published in 1869,[3][4] intending it to mean "better designed for an immediate, local environment".[5][6] Herbert Spencer first used the phrase – after reading Charles Darwin's On the Origin of Species – in his Principles of Biology of 1864[7] in which he drew parallels between his economic theories and Darwin's biological, evolutionary ones, writing, "This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection', or the preservation of favored races in the struggle for life."[1] In July 1866 Alfred Russel Wallace wrote to Darwin about readers thinking that the phrase "natural selection" personified nature as "selecting", and said this misconception could be avoided "by adopting Spencer's term" Survival of the fittest. Darwin promptly replied that Wallace's letter was "as clear as daylight. I fully agree with all that you say on the advantages of H. Spencer's excellent expression of 'the survival of the fittest'. This however had not occurred to me till reading your letter. It is, however, a great objection to this term that it cannot be used as a substantive governing a verb". Had he received the letter two months earlier, he would have worked the phrase into the fourth edition of the Origin which was then being printed, and he would use it in his "next book on Domestic Animals etc.".[1] Darwin wrote on page 6 of The Variation of Animals and Plants under Domestication published in 1868, "This preservation, during the battle for life, of varieties which possess any advantage in structure, constitution, or instinct, I have called Natural Selection; and Mr. Herbert Spencer has well expressed the same idea by the Survival of the Fittest. The term "natural selection" is in some respects a bad one, as it seems to imply conscious choice; but this will be disregarded after a little familiarity". He defended his analogy as similar to language used in chemistry, and to astronomers depicting the "attraction of gravity as ruling the movements of the planets", or the way in which "agriculturists speak of man making domestic races by his power of selection". He had "often personified the word Nature; for I have found it difficult to avoid this ambiguity; but I mean by nature only the aggregate action and product of many natural laws,—and by laws only the ascertained sequence of events."[2] In the first four editions of On the Origin of Species, Darwin had used the phrase "natural selection".[8] In Chapter 4 of the 5th edition of The Origin published in 1869,[3] Darwin implies again the synonym: "Natural Selection, or the Survival of the Fittest".[4] By "fittest" Darwin meant "better adapted for the immediate, local environment", not the common modern meaning of "in the best physical shape" (think of a puzzle piece, not an athlete).[5] In the introduction he gave full credit to Spencer, writing "I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man's power of selection. But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient."[9] In The Man Versus The State, Spencer used the phrase in a postscript to justify a plausible explanation of how his theories would not be adopted by "societies of militant type". He uses the term in the context of societies at war, and the form of his reference suggests that he is applying a general principle.[10] "Thus by survival of the fittest, the militant type of society becomes characterized by profound confidence in the governing power, joined with a loyalty causing submission to it in all matters whatever".[11] Though Spencer’s conception of organic evolution is commonly interpreted as a form of Lamarckism,[a] Herbert Spencer is sometimes credited with inaugurating Social Darwinism. The phrase "survival of the fittest" has become widely used in popular literature as a catchphrase for any topic related or analogous to evolution and natural selection. It has thus been applied to principles of unrestrained competition, and it has been used extensively by both proponents and opponents of Social Darwinism.[citation needed] Evolutionary biologists criticise the manner in which the term is used by non-scientists and the connotations that have grown around the term in popular culture. The phrase also does not help in conveying the complex nature of natural selection, so modern biologists prefer and almost exclusively use the term natural selection. The biological concept of fitness refers to reproductive success, as opposed to survival, and is not explicit in the specific ways in which organisms can be more "fit" (increase reproductive success) as having phenotypic characteristics that enhance survival and reproduction (which was the meaning that Spencer had in mind).[citation needed] While the phrase "survival of the fittest” is often used to refer to “natural selection”, it is avoided by modern biologists, because the phrase can be misleading. For example, “survival” is only one aspect of selection, and not always the most important. Another problem is that the word “fit” is frequently confused with a state of physical fitness. In the evolutionary meaning “fitness” is the rate of reproductive output among a class of genetic variants.[13] The phrase can also be interpreted to express a theory or hypothesis: that "fit" as opposed to "unfit" individuals or species, in some sense of "fit", will survive some test. Interpretations of the phrase as expressing a theory are in danger of being tautological, meaning roughly "those with a propensity to survive have a propensity to survive"; to have content the theory must use a concept of fitness that is independent of that of survival.[5][14] Interpreted as a theory of species survival, the theory that the fittest species survive is undermined by evidence that while direct competition is observed between individuals, populations and species, there is little evidence that competition has been the driving force in the evolution of large groups such as, for example, amphibians, reptiles, and mammals. Instead, these groups have evolved by expanding into empty ecological niches.[15] In the punctuated equilibrium model of environmental and biological change, the factor determining survival is often not superiority over another in competition but ability to survive dramatic changes in environmental conditions, such as after a meteor impact energetic enough to greatly change the environment globally. The main land dwelling animals to survive the K-Pg impact 66 million years ago had the ability to live in underground tunnels, for example. In 2010 Sahney et al. argued that there is little evidence that intrinsic, biological factors such as competition have been the driving force in the evolution of large groups. Instead, they cited extrinsic, abiotic factors such as expansion as the driving factor on a large evolutionary scale. The rise of dominant groups such as amphibians, reptiles, mammals and birds occurred by opportunistic expansion into empty ecological niches and the extinction of groups happened due to large shifts in the abiotic environment.[15] It has been claimed that "the survival of the fittest" theory in biology was interpreted by late 19th century capitalists as "an ethical precept that sanctioned cut-throat economic competition" and led to the advent of the theory of "social Darwinism" which was used to justify laissez-faire economics, war and racism. However, these ideas predate and commonly contradict Darwin's ideas, and indeed their proponents rarely invoked Darwin in support.[citation needed] The term "social Darwinism" referring to capitalist ideologies was introduced as a term of abuse by Richard Hofstadter's Social Darwinism in American Thought published in 1944.[16][17] Critics of theories of evolution have argued that "survival of the fittest" provides a justification for behaviour that undermines moral standards by letting the strong set standards of justice to the detriment of the weak.[18] However, any use of evolutionary descriptions to set moral standards would be a naturalistic fallacy (or more specifically the is–ought problem), as prescriptive moral statements cannot be derived from purely descriptive premises. Describing how things are does not imply that things ought to be that way. It is also suggested that "survival of the fittest" implies treating the weak badly, even though in some cases of good social behaviour – co-operating with others and treating them well – might improve evolutionary fitness.[16][19] Russian anarchist Peter Kropotkin viewed the concept of "survival of the fittest" as supporting co-operation rather than competition. In his book Mutual Aid: A Factor of Evolution he set out his analysis leading to the conclusion that the fittest was not necessarily the best at competing individually, but often the community made up of those best at working together. He concluded that In the animal world we have seen that the vast majority of species live in societies, and that they find in association the best arms for the struggle for life: understood, of course, in its wide Darwinian sense — not as a struggle for the sheer means of existence, but as a struggle against all natural conditions unfavourable to the species. The animal species, in which individual struggle has been reduced to its narrowest limits, and the practice of mutual aid has attained the greatest development, are invariably the most numerous, the most prosperous, and the most open to further progress. Applying this concept to human society, Kropotkin presented mutual aid as one of the dominant factors of evolution, the other being self-assertion, and concluded that In the practice of mutual aid, which we can retrace to the earliest beginnings of evolution, we thus find the positive and undoubted origin of our ethical conceptions; and we can affirm that in the ethical progress of man, mutual support not mutual struggle – has had the leading part. In its wide extension, even at the present time, we also see the best guarantee of a still loftier evolution of our race. "Survival of the fittest" is sometimes claimed to be a tautology.[20] The reasoning is that if one takes the term "fit" to mean "endowed with phenotypic characteristics which improve chances of survival and reproduction" (which is roughly how Spencer understood it), then "survival of the fittest" can simply be rewritten as "survival of those who are better equipped for surviving". Furthermore, the expression does become a tautology if one uses the most widely accepted definition of "fitness" in modern biology, namely reproductive success itself (rather than any set of characters conducive to this reproductive success). This reasoning is sometimes used to claim that Darwin's entire theory of evolution by natural selection is fundamentally tautological, and therefore devoid of any explanatory power.[20] However, the expression "survival of the fittest" (taken on its own and out of context) gives a very incomplete account of the mechanism of natural selection. The reason is that it does not mention a key requirement for natural selection, namely the requirement of heritability. It is true that the phrase "survival of the fittest", in and by itself, is a tautology if fitness is defined by survival and reproduction. Natural selection is the portion of variation in reproductive success that is caused by heritable characters (see the article on natural selection).[20] If certain heritable characters increase or decrease the chances of survival and reproduction of their bearers, then it follows mechanically (by definition of "heritable") that those characters that improve survival and reproduction will increase in frequency over generations. This is precisely what is called "evolution by natural selection." On the other hand, if the characters which lead to differential reproductive success are not heritable, then no meaningful evolution will occur, "survival of the fittest" or not: if improvement in reproductive success is caused by traits that are not heritable, then there is no reason why these traits should increase in frequency over generations. In other words, natural selection does not simply state that "survivors survive" or "reproducers reproduce"; rather, it states that "survivors survive, reproduce and therefore propagate any heritable characters which have affected their survival and reproductive success". This statement is not tautological: it hinges on the testable hypothesis that such fitness-impacting heritable variations actually exist (a hypothesis that has been amply confirmed.)[20] Momme von Sydow suggested further definitions of 'survival of the fittest' that may yield a testable meaning in biology and also in other areas where Darwinian processes have been influential. However, much care would be needed to disentangle tautological from testable aspects. Moreover, an "implicit shifting between a testable and an untestable interpretation can be an illicit tactic to immunize natural selection [...] while conveying the impression that one is concerned with testable hypotheses."[14][21] Skeptic Society founder and Skeptic magazine publisher Michael Shermer addresses the tautology problem in his 1997 book, Why People Believe Weird Things, in which he points out that although tautologies are sometimes the beginning of science, they are never the end, and that scientific principles like natural selection are testable and falsifiable by virtue of their predictive power. Shermer points out, as an example, that population genetics accurately demonstrate when natural selection will and will not effect change on a population. Shermer hypothesizes that if hominid fossils were found in the same geological strata as trilobites, it would be evidence against natural selection.[22] ^ a b c d "Letter 5140 – Wallace, A. R. to Darwin, C. R., 2 July 1866". Darwin Correspondence Project. Retrieved 12 January 2010. "Letter 5145 – Darwin, C. R. to Wallace, A. R., 5 July (1866)". Darwin Correspondence Project. Retrieved 12 January 2010.  ^ "Herbert Spencer in his Principles of Biology of 1864, vol. 1, p. 444, wrote: 'This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called "natural selection", or the preservation of favoured races in the struggle for life.'" Maurice E. Stucke, Better Competition Advocacy, retrieved 29 August 2007 , citing HERBERT SPENCER, THE PRINCIPLES OF BIOLOGY 444 (Univ. Press of the Pac. 2002.) ^ a b "This preservation, during the battle for life, of varieties which possess any advantage in structure, constitution, or instinct, I have called Natural Selection; and Mr. Herbert Spencer has well expressed the same idea by the Survival of the Fittest. The term "natural selection" is in some respects a bad one, as it seems to imply conscious choice; but this will be disregarded after a little familiarity." Darwin, Charles (1868), The Variation of Animals and Plants under Domestication, 1 (1st ed.), London: John Murray, p. 6, retrieved 10 August 2015  ^ a b Freeman, R. B. (1977), "On the Origin of Species", The Works of Charles Darwin: An Annotated Bibliographical Handlist (2nd ed.), Cannon House, Folkestone, Kent, England: Wm Dawson & Sons Ltd  ^ a b "This preservation of favourable variations, and the destruction of injurious variations, I call Natural Selection, or the Survival of the Fittest." – Darwin, Charles (1869), On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (5th ed.), London: John Murray, pp. 91–92, retrieved 22 February 2009  ^ a b c "Stephen Jay Gould, Darwin's Untimely Burial", 1976; from Philosophy of Biology:An Anthology, Alex Rosenberg, Robert Arp ed., John Wiley & Sons, May 2009, pp. 99–102. ^ "Evolutionary biologists customarily employ the metaphor 'survival of the fittest,' which has a precise meaning in the context of mathematical population genetics, as a shorthand expression when describing evolutionary processes." Chew, Matthew K.; Laubichler, Manfred D. (4 July 2003), "PERCEPTIONS OF SCIENCE: Natural Enemies — Metaphor or Misconception?", Science, 301 (5629): 52–53, doi:10.1126/science.1085274, PMID 12846231, retrieved 20 March 2008  ^ Vol. 1, p. 444 ^ U. Kutschera (14 March 2003), A Comparative Analysis of the Darwin-Wallace Papers and the Development of the Concept of Natural Selection (PDF), Institut für Biologie, Universität Kassel, Germany, archived from the original (PDF) on 14 April 2008, retrieved 20 March 2008  ^ Darwin, Charles (1869), On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (5th ed.), London: John Murray, p. 72  ^ The principle of natural selection applied to groups of individual is known as Group selection. ^ Herbert Spencer; Truxton Beale (1916), The Man Versus the State: A Collection of Essays, M. Kennerley  (snippet) ^ Federico Morganti (May 26, 2013). "Adaptation and Progress: Spencer's Criticism of Lamarck". Evolution & Cognition.  External link in |publisher= (help) ^ Colby, Chris (1996–1997), Introduction to Evolutionary Biology, TalkOrigins Archive, retrieved 22 February 2009  ^ a b von Sydow, M. (2014). ‘Survival of the Fittest’ in Darwinian Metaphysics – Tautology or Testable Theory? Archived 3 March 2016 at the Wayback Machine. (pp. 199–222) In E. Voigts, B. Schaff & M. Pietrzak-Franger (Eds.). Reflecting on Darwin. Farnham, London: Ashgate. ^ a b Sahney, S., Benton, M.J. and Ferry, P.A. (2010), "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land" (PDF), Biology Letters, 6 (4): 544–547, doi:10.1098/rsbl.2009.1024, PMC 2936204 , PMID 20106856. CS1 maint: Multiple names: authors list (link) ^ a b John S. Wilkins (1997), Evolution and Philosophy: Social Darwinism – Does evolution make might right?, TalkOrigins Archive, retrieved 21 November 2007  ^ Leonard, Thomas C. (2005), "Mistaking Eugenics for Social Darwinism: Why Eugenics is Missing from the History of American Economics" (PDF), History of Political Economy, 37 (supplement:): 200–233, doi:10.1215/00182702-37-Suppl_1-200  ^ Alan Keyes (7 July 2001), WorldNetDaily: Survival of the fittest?, WorldNetDaily, retrieved 19 November 2007  ^ Mark Isaak (2004), CA002: Survival of the fittest implies might makes right, TalkOrigins Archive, retrieved 19 November 2007  ^ a b c d Corey, Michael Anthony (1994), "Chapter 5. Natural Selection", Back to Darwin: the scientific case for Deistic evolution, Rowman and Littlefield, p. 147, ISBN 978-0-8191-9307-0  ^ Cf. von Sydow, M. (2012). From Darwinian Metaphysics towards Understanding the Evolution of Evolutionary Mechanisms. A Historical and Philosophical Analysis of Gene-Darwinism and Universal Darwinism. Universitätsverlag Göttingen. ^ Shermer, Michael; Why People Believe Weird Things; 1997; Pages 143–144

Survival

Jump to navigation Jump to search A grow light or plant light is an artificial light source, generally an electric light, designed to stimulate plant growth by emitting a light appropriate for photosynthesis. Grow lights are used in applications where there is either no naturally occurring light, or where supplemental light is required. For example, in the winter months when the available hours of daylight may be insufficient for the desired plant growth, lights are used to extend the time the plants receive light. If plants do not receive enough light, they will grow long and spindly.[citation needed] Grow lights either attempt to provide a light spectrum similar to that of the sun, or to provide a spectrum that is more tailored to the needs of the plants being cultivated. Outdoor conditions are mimicked with varying colour, temperatures and spectral outputs from the grow light, as well as varying the lumen output (intensity) of the lamps. Depending on the type of plant being cultivated, the stage of cultivation (e.g. the germination/vegetative phase or the flowering/fruiting phase), and the photoperiod required by the plants, specific ranges of spectrum, luminous efficacy and colour temperature are desirable for use with specific plants and time periods. Russian botanist Andrei Famintsyn was the first to use artificial light for plant growing and research (1868). Grow lights are used for horticulture, indoor gardening, plant propagation and food production, including indoor hydroponics and aquatic plants. Although most grow lights are used on an industrial level, they can also be used in households. According to the inverse-square law, the intensity of light radiating from a point source (in this case a bulb) that reaches a surface is inversely proportional to the square of the surface's distance from the source (if an object is twice as far away, it receives only a quarter the light) which is a serious hurdle for indoor growers, and many techniques are employed to use light as efficiently as possible. Reflectors are thus often used in the lights to maximize light efficiency. Plants or lights are moved as close together as possible so that they receive equal lighting and that all light coming from the lights falls on the plants rather than on the surrounding area. Example of an HPS grow light set up in a grow tent. The setup includes a carbon filter to remove odors, and ducting to exhaust hot air using a powerful exhaust fan. A range of bulb types can be used as grow lights, such as incandescents, fluorescent lights, high-intensity discharge lamps (HID), and light-emitting diodes (LED). Today, the most widely used lights for professional use are HIDs and fluorescents. Indoor flower and vegetable growers typically use high-pressure sodium (HPS/SON) and metal halide (MH) HID lights, but fluorescents and LEDs are replacing metal halides due to their efficiency and economy.[1] Metal halide lights are regularly used for the vegetative phase of plant growth, as they emit larger amounts of blue and ultraviolet radiation.[2][3] With the introduction of ceramic metal halide lighting and full-spectrum metal halide lighting, they are increasingly being utilized as an exclusive source of light for both vegetative and reproductive growth stages. Blue spectrum light may trigger a greater vegetative response in plants.[4][5][6] High-pressure sodium lights are also used as a single source of light throughout the vegetative and reproductive stages. As well, they may be used as an amendment to full-spectrum lighting during the reproductive stage. Red spectrum light may trigger a greater flowering response in plants.[7] If high-pressure sodium lights are used for the vegetative phase, plants grow slightly more quickly, but will have longer internodes, and may be longer overall. In recent years LED technology has been introduced into the grow light market. By designing an indoor grow light using diodes, specific wavelengths of light can be produced. NASA has tested LED grow lights for their high efficiency in growing food in space for extraterrestrial colonization. Findings showed that plants are affected by light in the red, green and blue parts of the visible light spectrum.[8][9] While fluorescent lighting used to be the most common type of indoor grow light, HID lights are now the most popular.[10] High intensity discharge lamps have a high lumen-per-watt efficiency.[11] There are several different types of HID lights including mercury vapor, metal halide, high pressure sodium and conversion bulbs. Metal halide and HPS lamps produce a color spectrum that is somewhat comparable to the sun and can be used to grow plants. Mercury vapor lamps were the first type of HIDs and were widely used for street lighting, but when it comes to indoor gardening they produce a relatively poor spectrum for plant growth so they have been mostly replaced by other types of HIDs for growing plants.[11] All HID grow lights require a ballast to operate, and each ballast has a particular wattage. Popular HID wattages include 150W, 250W, 400W, 600W and 1000W. Of all the sizes, 600W HID lights are the most electrically efficient as far as light produced, followed by 1000W. A 600W HPS produces 7% more light (watt-for-watt) than a 1000W HPS.[11] Although all HID lamps work on the same principle, the different types of bulbs have different starting and voltage requirements, as well as different operating characteristics and physical shape. Because of this a bulb won't work properly unless it's using a matching ballast, even if the bulb will physically screw in. In addition to producing lower levels of light, mismatched bulbs and ballasts will stop working early, or may even burn out immediately.[11] 400W Metal halide bulb compared to smaller incandescent bulb Metal halide bulbs are a type of HID light that emit light in the blue and violet parts of the light spectrum, which is similar to the light that is available outdoors during spring.[12] Because their light mimics the color spectrum of the sun, some growers find that plants look more pleasing under a metal halide than other types of HID lights such as the HPS which distort the color of plants. Therefore, it's more common for a metal halide to be used when the plants are on display in the home (for example with ornamental plants) and natural color is preferred.[13] Metal halide bulbs need to be replaced about once a year, compared to HPS lights which last twice as long.[13] Metal halide lamps are widely used in the horticultural industry and are well-suited to supporting plants in earlier developmental stages by promoting stronger roots, better resistance against disease and more compact growth.[12] The blue spectrum of light encourages compact, leafy growth and may be better suited to growing vegetative plants with lots of foliage.[13] A metal halide bulb produces 60-125 lumens/watt, depending on the wattage of the bulb.[14] They are now being made for digital ballasts in a pulse start version, which have higher electrical efficiency (up to 110 lumens per watt) and faster warmup.[15] One common example of a pulse start metal halide is the ceramic metal halide (CMH). Pulse start metal halide bulbs can come in any desired spectrum from cool white (7000 K) to warm white (3000 K) and even ultraviolet-heavy (10,000 K).[citation needed] Ceramic metal halide (CMH) lamps are a relatively new type of HID lighting, and the technology is referred to by a few names when it comes to grow lights, including ceramic discharge metal halide (CDM),[16] ceramic arc metal halide. Ceramic metal halide lights are started with a pulse-starter, just like other "pulse-start" metal halides.[16] The discharge of a ceramic metal halide bulb is contained in a type of ceramic material known as polycrystalline alumina (PCA), which is similar to the material used for an HPS. PCA reduces sodium loss, which in turn reduces color shift and variation compared to standard MH bulbs.[15] Horticultural CDM offerings from companies such as Philips have proven to be effective sources of growth light for medium-wattage applications.[17] Combination HPS/MH lights combine a metal halide and a high-pressure sodium in the same bulb, providing both red and blue spectrums in a single HID lamp. The combination of blue metal halide light and red high-pressure sodium light is an attempt to provide a very wide spectrum within a single lamp. This allows for a single bulb solution throughout the entire life cycle of the plant, from vegetative growth through flowering. There are potential tradeoffs for the convenience of a single bulb in terms of yield. There are however some qualitative benefits that come for the wider light spectrum. An HPS (High Pressure Sodium) grow light bulb in an air-cooled reflector with hammer finish. The yellowish light is the signature color produced by an HPS. High-pressure sodium lights are a more efficient type of HID lighting than metal halides. HPS bulbs emit light in the yellow/red visible light as well as small portions of all other visible light. Since HPS grow lights deliver more energy in the red part of the light spectrum, they may promote blooming and fruiting.[10] They are used as a supplement to natural daylight in greenhouse lighting and full-spectrum lighting(metal halide) or, as a standalone source of light for indoors/grow chambers. HPS grow lights are sold in the following sizes: 150W, 250W, 400W, 600W and 1000W.[10] Of all the sizes, 600W HID lights are the most electrically efficient as far as light produced, followed by 1000W. A 600W HPS produces 7% more light (watt-for-watt) than a 1000W HPS.[11] A 600W High Pressure Sodium bulbAn HPS bulb produces 60-140 lumens/watt, depending on the wattage of the bulb.[18] Plants grown under HPS lights tend to elongate from the lack of blue/ultraviolet radiation. Modern horticultural HPS lamps have a much better adjusted spectrum for plant growth. The majority of HPS lamps while providing good growth, offer poor color rendering index (CRI) rendering. As a result, the yellowish light of an HPS can make monitoring plant health indoors more difficult. CRI isn't an issue when HPS lamps are used as supplemental lighting in greenhouses which make use of natural daylight (which offsets the yellow light of the HPS). High-pressure sodium lights have a long usable bulb life, and six times more light output per watt of energy consumed than a standard incandescent grow light. Due to their high efficiency and the fact that plants grown in greenhouses get all the blue light they need naturally, these lights are the preferred supplemental greenhouse lights. But, in the higher latitudes, there are periods of the year where sunlight is scarce, and additional sources of light are indicated for proper growth. HPS lights may cause distinctive infrared and optical signatures, which can attract insects or other species of pests; these may in turn threaten the plants being grown. High-pressure sodium lights emit a lot of heat, which can cause leggier growth, although this can be controlled by using special air-cooled bulb reflectors or enclosures. Conversion bulbs are manufactured so they work with either a MH or HPS ballast. A grower can run an HPS conversion bulb on a MH ballast, or a MH conversion bulb on a HPS ballast. The difference between the ballasts is an HPS ballast has an igniter which ignites the sodium in an HPS bulb, while a MH ballast does not. Because of this, all electrical ballasts can fire MH bulbs, but only a Switchable or HPS ballast can fire an HPS bulb without a conversion bulb.[19] Usually a metal halide conversion bulb will be used in an HPS ballast since the MH conversion bulbs are more common. A switchable ballast is an HID ballast can be used with either a metal halide or an HPS bulb of equivalent wattage. So a 600W Switchable ballast would work with either a 600W MH or HPS.[10] Growers use these fixtures for propagating and vegetatively growing plants under the metal halide, then switching to a high-pressure sodium bulb for the fruiting or flowering stage of plant growth. To change between the lights, only the bulb needs changing and a switch needs to be set to the appropriate setting. Two plants growing under an LED grow light LED grow lights are composed of light-emitting diodes, usually in a casing with a heat sink and built-in fans. LED grow lights do not usually require a separate ballast and can be plugged directly into a standard electrical socket. LED grow lights vary in color depending on the intended use. It is known from the study of photomorphogenesis that green, red, far-red and blue light spectra have an effect on root formation, plant growth, and flowering, but there are not enough scientific studies or field-tested trials using LED grow lights to recommended specific color ratios for optimal plant growth under LED grow lights.[20] It has been shown that many plants will grow normally if given both red and blue light.[21][22][23] However, many studies indicate that red and blue light only provides the most cost efficient method of growth, plant growth is still better under light supplemented with green.[24][25][26] White LED grow lights provide a full spectrum of light designed to mimic natural light, providing plants a balanced spectrum of red, blue and green. The spectrum used varies, however, white LED grow lights are designed to emit similar amounts of red and blue light with the added green light to appear white. White LED grow lights are often used for supplemental lighting in home and office spaces. A large number of plant species have been assessed in greenhouse trials to make sure plants have higher quality in biomass and biochemical ingredients even higher or comparable with field conditions. Plant performance of mint, basil, lentil, lettuce, cabbage, parsley, carrot were measured by assessing health and vigor of plants and success in promoting growth. Promoting in profuse flowering of select ornamentals including primula, marigold, stock were also noticed.[27] In tests conducted by Philips Lighting on LED grow lights to find an optimal light recipe for growing various vegetables in greenhouses, they found that the following aspects of light affects both plant growth (photosynthesis) and plant development (morphology): light intensity, total light over time, light at which moment of the day, light/dark period per day, light quality (spectrum), light direction and light distribution over the plants. However it's noted that in tests between tomatoes, mini cucumbers and bell peppers, the optimal light recipe was not the same for all plants, and varied depending on both the crop and the region, so currently they must optimize LED lighting in greenhouses based on trial and error. They've shown that LED light affects disease resistance, taste and nutritional levels, but as of 2014 they haven't found a practical way to use that information.[28] Ficus plant grown under a white LED grow light. The diodes used in initial LED grow light designs were usually 1/3 watt to 1 watt in power. However, higher wattage diodes such as 3 watt and 5 watt diodes are now commonly used in LED grow lights. for highly compacted areas, COB chips between 10 watts and 100 watts can be used. Because of heat dissipation, these chips are often less efficient. LED grow lights should be kept at least 12 inches (30 cm) away from plants to prevent leaf burn.[13] Historically, LED lighting was very expensive, but costs have greatly reduced over time, and their longevity has made them more popular. LED grow lights are often priced higher, watt-for-watt, than other LED lighting, due to design features that help them to be more energy efficient and last longer. In particular, because LED grow lights are relatively high power, LED grow lights are often equipped with cooling systems, as low temperature improves both the brightness and longevity. LEDs usually last for 50,000 - 90,000 hours until LM-70 is reached.[citation needed] Fluorescent grow light Fluorescent lights come in many form factors, including long, thin bulbs as well as smaller spiral shaped bulbs (compact fluorescent lights). Fluorescent lights are available in color temperatures ranging from 2700 K to 10,000 K. The luminous efficacy ranges from 30 lm/W to 90 lm/W. The two main types of fluorescent lights used for growing plants are the tube-style lights and compact fluorescent lights. Fluorescent grow lights are not as intense as HID lights and are usually used for growing vegetables and herbs indoors, or for starting seedlings to get a jump start on spring plantings. A ballast is needed to run these types of fluorescent lights.[18] Standard fluorescent lighting comes in multiple form factors, including the T5, T8 and T12. The brightest version is the T5. The T8 and T12 are less powerful and are more suited to plants with lower light needs. High-output fluorescent lights produce twice as much light as standard fluorescent lights. A high-output fluorescent fixture has a very thin profile, making it useful in vertically limited areas. Fluorescents have an average usable life span of up to 20,000 hours. A fluorescent grow light produces 33-100 lumens/watt, depending on the form factor and wattage.[14] Dual spectrum compact fluorescent grow light. Actual length is about 40 cm (16 in) Standard Compact Fluorescent Light Compact Fluorescent lights (CFLs) are smaller versions of fluorescent lights that were originally designed as pre-heat lamps, but are now available in rapid-start form. CFLs have largely replaced incandescent light bulbs in households because they last longer and are much more electrically efficient.[18] In some cases, CFLs are also used as grow lights. Like standard fluorescent lights, they are useful for propagation and situations where relatively low light levels are needed. While standard CFLs in small sizes can be used to grow plants, there are also now CFL lamps made specifically for growing plants. Often these larger compact fluorescent bulbs are sold with specially designed reflectors that direct light to plants, much like HID lights. Common CFL grow lamp sizes include 125W, 200W, 250W and 300W. Unlike HID lights, CFLs fit in a standard mogul light socket and don't need a separate ballast.[10] Compact fluorescent bulbs are available in warm/red (2700 K), full spectrum or daylight (5000 K) and cool/blue (6500 K) versions. Warm red spectrum is recommended for flowering, and cool blue spectrum is recommended for vegetative growth.[10] Usable life span for compact fluorescent grow lights is about 10,000 hours.[18] A CFL produces 44-80 lumens/watt, depending on the wattage of the bulb.[14] Examples of lumens and lumens/watt for different size CFLs: Cold Cathode Fluorescent Light (CCFL) A cold cathode is a cathode that is not electrically heated by a filament. A cathode may be considered "cold" if it emits more electrons than can be supplied by thermionic emissionalone. It is used in gas-discharge lamps, such as neon lamps, discharge tubes, and some types of vacuum tube. The other type of cathode is a hot cathode, which is heated by electric current passing through a filament. A cold cathode does not necessarily operate at a low temperature: it is often heated to its operating temperature by other methods, such as the current passing from the cathode into the gas. The color temperatures of different grow lights Different grow lights produce different spectrums of light. Plant growth patterns can respond to the color spectrum of light, a process completely separate from photosynthesis known as photomorphogenesis.[29] Natural daylight has a high color temperature (approximately 5000-5800 K). Visible light color varies according to the weather and the angle of the Sun, and specific quantities of light (measured in lumens) stimulate photosynthesis. Distance from the sun has little effect on seasonal changes in the quality and quantity of light and the resulting plant behavior during those seasons. The axis of the Earth is not perpendicular to the plane of its orbit around the sun. During half of the year the north pole is tilted towards sun so the northern hemisphere gets nearly direct sunlight and the southern hemisphere gets oblique sunlight that must travel through more atmosphere before it reaches the Earth's surface. In the other half of the year, this is reversed. The color spectrum of visible light that the sun emits does not change, only the quantity (more during the summer and less in winter) and quality of overall light reaching the Earth's surface. Some supplemental LED grow lights in vertical greenhouses produce a combination of only red and blue wavelengths.[30] The color rendering index facilitates comparison of how closely the light matches the natural color of regular sunlight. The ability of a plant to absorb light varies with species and environment, however, the general measurement for the light quality as it affects plants is the PAR value, or Photosynthetically Active Radiation. There have been several experiments using LEDs to grow plants, and it has been shown that plants need both red and blue light for healthy growth. From experiments it has been consistently found that the plants that are growing only under LEDs red (660 nm, long waves) spectrum growing poorly with leaf deformities, though adding a small amount of blue allows most plants to grow normally.[24] Several reports suggest that a minimum blue light requirement of 15-30 µmol·m−2·s−1 is necessary for normal development in several plant species.[23][31][32] LED panel light source used in an experiment on potato plant growth by NASA Many studies indicate that even with blue light added to red LEDs, plant growth is still better under white light, or light supplemented with green.[24][25][26] Neil C Yorio demonstrated that by adding 10% blue light (400 to 500 nm) to the red light (660 nm) in LEDs, certain plants like lettuce[21] and wheat[22] grow normally, producing the same dry weight as control plants grown under full spectrum light. However, other plants like radish and spinach grow poorly, and although they did better under 10% blue light than red-only light, they still produced significantly lower dry weights compared to control plants under a full spectrum light. Yorio speculates there may be additional spectra of light that some plants need for optimal growth.[21] Greg D. Goins examined the growth and seed yield of Arabidopsis plants grown from seed to seed under red LED lights with 0%, 1%, or 10% blue spectrum light. Arabidopsis plants grown under only red LEDS alone produced seeds, but had unhealthy leaves, and plants took twice as long to start flowering compared to the other plants in the experiment that had access to blue light. Plants grown with 10% blue light produced half the seeds of those grown under full spectrum, and those with 0% or 1% blue light produced one-tenth the seeds of the full spectrum plants. The seeds all germinated at a high rate under all light types tested.[23] Hyeon-Hye Kim demonstrated that the addition of 24% green light (500-600 nm) to red and blue LEDs enhanced the growth of lettuce plants. These RGB treated plants not only produced higher dry and wet weight and greater leaf area than plants grown under just red and blue LEDs, they also produced more than control plants grown under cool white fluorescent lamps, which are the typical standard for full spectrum light in plant research.[25][26] She reported that the addition of green light also makes it easier to see if the plant is healthy since leaves appear green and normal. However, giving nearly all green light (86%) to lettuce produced lower yields than all the other groups.[25] The National Aeronautics and Space Administration’s (NASA) Biological Sciences research group has concluded that light sources consisting of more than 50% green cause reductions in plant growth, whereas combinations including up to 24% green enhance growth for some species.[33] Green light has been shown to affect plant processes via both cryptochrome-dependent and cryptochrome-independent means. Generally, the effects of green light are the opposite of those directed by red and blue wavebands, and it's speculated that green light works in orchestration with red and blue.[34] Absorbance spectra of free chlorophyll a (blue) and b (red) in a solvent. The action spectra of chlorophyll molecules are slightly modified in vivo depending on specific pigment-protein interactions. A plant's specific needs determine which lighting is most appropriate for optimum growth. If a plant does not get enough light, it will not grow, regardless of other conditions. Most plants use chlorophyll which mostly reflects green light, but absorbs red and blue light well. Vegetables grow best in strong sunlight, and to flourish indoors they need sufficient light levels, whereas foliage plants (e.g. Philodendron) grow in full shade and can grow normally with much lower light levels. Grow lights usage is dependent on the plant's phase of growth. Generally speaking, during the seedling/clone phase, plants should receive 16+ hours on, 8- hours off. The vegetative phase typically requires 18 hours on, and 6 hours off. During the final, flower stage of growth, keeping grow lights on for 12 hours on and 12 hours off is recommended.[citation needed] In addition, many plants also require both dark and light periods, an effect known as photoperiodism, to trigger flowering. Therefore, lights may be turned on or off at set times. The optimum photo/dark period ratio depends on the species and variety of plant, as some prefer long days and short nights and others prefer the opposite or intermediate "day lengths". Much emphasis is placed on photoperiod when discussing plant development. However, it is the number of hours of darkness that affects a plant’s response to day length.[35] In general, a “short-day” is one in which the photoperiod is no more than 12 hours. A “long-day” is one in which the photoperiod is no less than 14 hours. Short-day plants are those that flower when the day length is less than a critical duration. Long-day plants are those that only flower when the photoperiod is greater than a critical duration. Day-neutral plants are those that flower regardless of photoperiod.[36] Plants that flower in response to photoperiod may have a facultative or obligate response. A facultative response means that a plant will eventually flower regardless of photoperiod, but will flower faster if grown under a particular photoperiod. An obligate response means that the plant will only flower if grown under a certain photoperiod.[37] Main article: Photosynthetically active radiation Weighting factor for photosynthesis. The photon-weighted curve is for converting PPFD to YPF; the energy-weighted curve is for weighting PAR expressed in watts or joules. Lux and lumens are commonly used to measure light levels, but they are photometric units which measure the intensity of light as perceived by the human eye. The spectral levels of light that can be used by plants for photosynthesis is similar to, but not the same as what's measured by lumens. Therefore, when it comes to measuring the amount of light available to plants for photosynthesis, biologists often measure the amount of photosynthetically active radiation (PAR) received by a plant.[38] PAR designates the spectral range of solar radiation from 400 to 700 nanometers, which generally corresponds to the spectral range that photosynthetic organisms are able to use in the process of photosynthesis. The irradiance of PAR can be expressed in units of energy flux (W/m2), which is relevant in energy-balance considerations for photosynthetic organisms. However, photosynthesis is a quantum process and the chemical reactions of photosynthesis are more dependent on the number of photons than the amount of energy contained in the photons.[38] Therefore, plant biologists often quantify PAR using the number of photons in the 400-700 nm range received by a surface for a specified amount of time, or the Photosynthetic Photon Flux Density (PPFD).[38] This is normally measured using mol m−2s−1. According to one manufacturer of grow lights, plants require at least light levels between 100 and 800 μmol m−2s−1.[39] For daylight-spectrum (5800 K) lamps, this would be equivalent to 5800 to 46,000 lm/m2.

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