Bad News About LED vs HPS

Abiqua said:

Feigning ignorance doesn't compute....are you saying you cant increase your knowledge to improve your growing...or am I taking that all wrong?

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Abiqua said:

There is too much Blue light in White light....and not enough green and red with efficacy, which the plants seem, seem to want.....

Here is that paper, some have dropped but little have "read".....

Green Light Drives Leaf Photosynthesis More Effi ciently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green
https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/pcp/50/4/10.1093_pcp_pcp034/2/pcp034.pdf?Expires=1502177472&Signature=KORzgKyhVRp2sWyY0zhMxFrbx33feNoFka88o-0Y5m1FA-mliC-QvCDjwUwCqjgE~r7TMu9XPZK0uaqbVDTTarlOXGDY44jlHEBk6PVfYAdrmALmXQ1sdg9lXne95Me9XK3gt9hUdH7znZe3jpLorZeWd2RGnS6vCaX-nhaCYWJajFy-lLCR0GvWziNTkkASEg45RASJkmRZ-nef6gGcxSUSsNfPX~mxmw4tvCgbYx-uIXDC2xQA2FinTTGrlHnUMssNnwFa6N8L8jls7bLFjzXVl0LE1DfCo~AB8qHMWlF61XtCg1Uy022bF4FUyqLceO2tFtD-rCuPcCkWoH1ApA__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q


Moreover, as already mentioned above, it has been clearly shown that the quantum yield of photosynthesis based on absorbed photosynthetically active photon fl ux density (PPFD), measured at low PPFDs, was comparable between green and red light. When measured in leaves grown under natural conditions, particularly for those of trees, the quantum yield of green light is considerably greater than that of blue light ( Inada 1976 ), because some fraction of blue light is absorbed by fl avonoids in vacuoles and/or carotenoids in chloroplast envelopes.
Moreover, some carotenoids in thylakoid membranes do not transfer energy to reaction centers, or transfer with an effi ciency signifi cantly less than 1.0 ( Akimoto and Mimuro 2005 ). For example, one of the most abundant carotenoids in thylakoids, lutein, transfers its energy to chlorophyll with an effi - ciency of 0.7 ( Akimoto et al. 2005 ). The effi ciency for neoxanthin is even less, at most 0.09 ( Akimoto et al. 2005 ). Accumulation of fl avonoids and carotenoids is well known to increase in response to ultraviolet and/or strong light ( Lambers et al. 2008 ). This probably explains to a considerable extent why the quantum yield of blue light is low. Evans and Anderson (1987) reconstructed the absorbance spectrum of thylakoid membranes from those of the chlorophyll–protein complexes and estimated the relative excitation of PSII and PSI.
Evans (1987) argued that imbalance of PSII/PSI excitation would occur at wavelengths where light is absorbed by Chl b because energy is preferentially transferred to PSII. This might also explain why the quantum yield of blue light on an absorbed quantum basis is low. If this effect is large, a decrease in the PSII quantum yield (Genty's parameter, see below) might be expected at wavelengths strongly absorbed by Chl b . In a preliminary study with rice leaf discs illuminated with monochoromatic lights at a low PPFD of 5–12 µ mol m –2 s –1 , Fig. 2 Model explaining the détour effect on absorptance. Left: no détour effect. Right: the light path is lengthened 3-fold by the détour effect. For strongly absorbed monochromatic light, the increase in absorptance by the détour effect is small (above), while for weakly absorbed light the increase is marked (below). 686 I. Terashima et al. Plant Cell Physiol. 50(4): 684–697 (2009) doi:10.1093/pcp/pcp034 © The Author 2009. we observed small reduction of the PSII reaction center [decreased ( Fm′ – Fs ′ )/ Fm′ mainly due to the decrease in photochemical quenching] in two wavelength regions with peaks at 470 and 650 nm, respectively, implying overexcitation of PSII at these wavelengths. However, the decreases observed were not enough to account for the large decrease in the quantum yield of blue light.

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mauricem00 said:

interesting. this argument proves that natural sunlight is bad for plants because it contains too much blue and violet. just reinforces my belief that the gardener and janitor at the university were smarter than most of my professors.all these studies and theories are based on short term exposure to monochromatic light.any engineer will tel you that theory is a good starting post but in the real world testing and tweaking is needed to make designs work as intended. lettuce grows well under 2 band (450/660nm) lights. but fruiting and flowering plants do not

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BobCajun said:

The plants have never looked healthier than they do under the 1/2 minus green HPS. The leaves are perfectly green all over, meaning no signs of burning or bleaching. My wattage now is the 150w HPS with two 14w LED bulbs on top, to fill in the ends and provide more blue (5000k), and two on the bottom pointing upward to prevent dark zones. So 206w altogether. With the filter, the HPS output may be reduced to a little over 100w of light. So still probably about 160w worth of light in a 3"x 1.5" area. No signs of too little light, buds are looking normal. I think I was using way too much light before. The water usage is also down considerably.

Actually the reduced water transpiration may be preventing nute burn. The more water gets pulled up to cool the leaves, the more nutes are pulled up with it. Which is something to think about when choosing circulation fans or when using high wattages of light.

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Daylee said:

lol some of there arguments are just pure gold

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InTheValley said:

whats lec?

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ZeroTrousers said:

Light emitting ceramic

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Daylee said:

lol some of there arguments are just pure gold

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mauricem00 said:

you forgot to factor in ballast lost which is factored into T5 ratings. a 315 cmh produces 33000 lumens and draws 355 watts from the wall. (93LPW)

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CobKits said:

thanks maurice that was super informative i didnt realize the huge discrepancy in T5 efficiency and agree that any one built as a grow light uses the cheapest shoddiest bulbs and ballasts

i was looking more closely at the CMH numbers, my cmh ballasts (hydrofarm) dont draw 355W from the wall, more like 335-340W at the wall, and is a square wave output which makes the output more efficient. on a bulb basis alone, the cmhs are almost 110 lm/W initally and maintain 95% of this after 2 full years of flowering. with a ballast around 93% efficient youre up around 99 lm/W of high-cri light at mean bulb life after 1 year of use

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i was digging a bit into GEs product data, and while i do see bulbs that are 4800 lumens that is initial not mean. traditionally fluorescents drop off steeply and then hold (as opposed to CMHs which are more linear). So the 4400 lumen mean data GE provides is probably more accurate. i dont know if the programmed start ballasts help with this lumen maintenance issues

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so using the 4400 mean lumens it seems that CMH and the best T5 are right in the same wheelhouse

Whether lumens translates into usable PAR is another story. CMH has lots of green light but the spectrum is more uniform than T5 with a green peak centered wright where lumens are measured. also worth consideration with the "green inhibition" noted in this thread

would be a good side by side of one of the more efficient T5 setups vs a 315. what do those HQ bulbs and ballasts cost typically?

obviously DE HPS and LED with system efficiencies of 130-160+ lm/W are in a class of their own

that HQ T5 info should get out there. easy retrofit of ballast and bulbs into the shit ton of fixtures out there, and the spectrum of fluorescent (and mellow uniform lighting) is a proven performer for rooting and early veg

there seems to be somethign about the CMH spectra though. As ive mentioned ive seen people hit 1.4 GPW with rooms of 315s, ive never seen that with T5s (ive also never seen anyone using those super efficient T5s

heres a link (a few years old) where GE claims the T8 is even better (pg 23). im sure this info is somewhat dated

https://ewh.ieee.org/r3/atlanta/ias/Whats New in Lighting w_ LED.pdf

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