MrYuk

The "Last Update" at the top of the FAQ is 12/3/06 but I'm assuming it's supposed to be 12/3/05

You know, some day I'll learn that the way I write the date isn't the only way to write it...sorry bout that.

frendofthedevil

12th of March

MrYuk

Whoops. Sometimes I don't think before I post. Thanks. :-)

C_ka

Hey thought this might be worthy of an entry, i.e how much light.

took me ages to figure out what was wrong with mine, by that time they were gonners. maybe it will save a noob like me. Never seen it on any other grow FAQs, but then, my memorys pretty shoddy.....

So i had some problems with my shit, going yellow and stuff, not burning, temps were 28*C max. plants were turning yellow, new growth came out green, then turned yellow, shaded underside of stems were still green.

everyone told me nute def, nute burn, waterlogged ect, but...

found a paper about photoinhibition, quite the interesting, seems to say the more light used, the less efficently the plant photosynthysises....


http://www.fsl.orst.edu/~bond/fs561/...alves-etal.pdf


"The use of the quantum absorbed by the leaf results in a
hyperbolic response of photosynthesis to light (Farquhar et al., 1980). Under low-intensity light (less than 100
mol.m.2s.1), more than 80% of the absorbed quantum can be used in photosynthesis, according to the maximum quantum efficiency in releasing O2 (Björkman & Demmig-Adams, 1987); when light intensity approaches 1000
mol.m.2s.1 (50% of the full sunlight value), less than 25% of the absorbed quantum is used; and, under full sunlight, utilization decreases to 10% (Long et al., 1994)."


"In practice, the consequences of photoinhibition are: reduced maximum quantum efficiency for CO
2 absorption () and release of O2 (0); decreased convexity () in the response curve of photosynthesis to light; reduced photochemical activity of PS II (Fv/Fm, ratio of fluorescence of chlorophyll a); and, with long exposure to excess light, decreased maximum photosynthetic rate (PSmax) (Boese & Huner, 1992; Long et al., 1994). The decreases of , 0, and Fv/Fm were noticed preceding reduction in PSmax;"


"A prolonged exposure of plants or organisms to excessive radiation may result in the photodestruction of the photosynthetic pigments, since the discoloration (bleaching) of these pigments depends on oxygen and light; this phenomenon is normally called .photooxidation,. and it may cause the death of the cell or the organism (Powles, 1984; Hendrey et al., 1987)."


"In most cases, photooxidation is a secondary phenomenon, occurring after a slow phase during which there is already a decrease of the photosynthetic activity dependent on light intensity and exposure time, but without any changes in the pigment pool (Powles, 1984; Long et al., 1994). Therefore, photoinhibition of photosynthesis does not appear after the destruction of the pool of pigments; on the contrary, the bleaching of pigments occurs when a certain degree of photoinhibition has already occurred (Hendrey et al., 1987)."


So the lesson, dont use 123W sq/ft HPS!!!! (i.e 400w in a closet) after about 65Wsqft wasting time, and prob reducing photosynthysis effecency.

Cheers guys, if this is worthy and you want a more stremlined FAQ type thing tell me and i'll wip it up.. (prob get some pics as well)

__________________
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Thepizzaguy

Just a friendly BUMP!