what's up with more red than blue?

Rahz

Well-Known Member
I've read a few university papers on the subject, though the plants used vary. In one study strawberry plants were grown under both blue or red light. Plants were cut up and separated into leaf, stem, and bud. The blue dominant light produced the heaviest leaf weight while the red dominant light produced the heaviest stem weight. This follows the general idea that blue light promoted close internodes.

For the veg period the light a person chooses may depend on what they're trying to accomplish. For instance, in a sog a balanced spectrum (3:1) in veg and flower might be a good idea. If you are only growing a few plants in a scrog and want the plants to veg with longer internodes going heavy on red for the first 3 weeks might be a good idea. That vertical growth under the screen can be translated in lateral growth. Once the screen is full a more balanced spectrum would be appropriate going into flower so internodes shorten and leaf matter bulks up a bit as the buds are getting started.

I've been using 3000K t5s for the whole grow and suspect either the light is just weak, or there's not a whole lot of blue as I get fantastic (desired) stretch in veg and then fantastic (undesired) stretch going into bud production. Looking at some spectral charts the CFLs don't have the same full bodied spectrum white LEDs have and get their rating by mixing relatively narrow bands of red, green, blue. In some charts for 3000K bulbs green is used more than blue to achieve the Kelvin rating. In the Cree3050 100watt LED thread you can see how the 2700K spectrum produces nice unstretched plants while I'm getting 5 foot monster plants growing under 3000Ks.

So even the K rating isn't going to be an absolute indicator of anything. I'll probably be using 3000K cfls for veg to get my stretch and then switch to 2700K LEDs for flower! Ain't that something?
 

rashomon

Active Member
...[KNNA] were starting from scratch and empirical studies were the quickest way to get a ballpark idea of which spectra were the best for which stage of growth.
Does anyone have the link for lighting for different stages of growth?

Thanks, SupraSPL, for sharing the XLM2's that you use. Although only 350ma? Those are rated up to 3000 (as I'm sure you know). You may not want to go full 3000 but why not at least 1500, get a lot of light from them, right? I'm not sure what you meant by "TJ of about 40c."

Rahz, thanks for detailing some of those motivations out for me. Makes a lot of sense!

Again, thanks, and sorry for so many questions. I've been lurking here for many years in search of these answers--been too afraid to ask!

What about for vegetative growth using cool-whites + a few warm-whites? Or is there a reason neutrals are better than cool (perhaps their fuller spectrum seems to work better, assuming blues loose a lot of full spectrum for that 450nm punch.)
 

rashomon

Active Member
"[h=3]Conclusions[/h]In this study, blue light has been shown to trigger both a qualitative signalling effect enabling normal photosynthetic functioning of cucumber leaves and a quantitative response stimulating leaf development normally associated with acclimation to irradiance intensity. Leaf acclimation to irradiance intensity may therefore be regulated by a limited range of wavelengths instead of the full PAR spectrum. Varying the blue light fraction offers the possibility to manipulate leaf properties under a low irradiance such that they would normally be associated with high irradiances. The possibility to grow plants under relatively low irradiance in a plant growth facility, with a relatively high photosynthetic capacity able to withstand irradiances under field conditions, is a useful practical consequence for research and agriculture."

Thank you!!
 

Thecouchlock

Well-Known Member
Advanced LED 300w work very well for me, just thought I would throw it out there. The frostiest I have ever seen :D
 

SupraSPL

Well-Known Member
Thanks, SupraSPL, for sharing the XLM2's that you use. Although only 350ma? Those are rated up to 3000 (as I'm sure you know). You may not want to go full 3000 but why not at least 1500, get a lot of light from them, right? I'm not sure what you meant by "TJ of about 40c."
This lamp was designed as a work light but now that winter has come it is growing bell peppers, bush beans and seedlings. I gave it enough heatsink to be driven at 1050mA for an indefinite time or driven harder for a short time. So I can switch out the driver for taller plants.

The Tj is the junction temp inside the LED. Manufacturer spec sheets show how the efficiency of the LED is affected by the junction temp (temp droop). 85C is considered a normal operating temp for modern blue/white LEDs but if you can manage to run them cooler you gain efficiency over those numbers. For the XML2 you gain 7% at 50c.

Another advantage to running them cool is lumen maintenance. Light sources lose output over time but continue to draw the same amount of electricity. Fluorescent and HID bulbs have a much lower lumen maintenance than LEDs run cool. The XML2 loses 1.5% in 250 days of 12/12 if run at 85C. I estimate that it will lose no more than 5% if run at 50C for 10 years. This chart show no loss after 18 months of continuous use at 55c.

What about for vegetative growth using cool-whites + a few warm-whites? Or is there a reason neutrals are better than cool (perhaps their fuller spectrum seems to work better, assuming blues loose a lot of full spectrum for that 450nm punch.)
4500K 4200K 3700K 3200K 3000K I believe they would all work well and mixing them would probably improve the efficiency slightly. One thing to consider though, Mr Flux's work has show that very cool, very warm and Hi CRI LEDs have a lower LER and ultimately a lower radiometric efficiency.
 

rashomon

Active Member
All great info. Thanks to everyone who's contributed to this thread. I believe I do have a much better understand to my original questions. All-in-all I feel balanced lights holds keys we yet too understand. And for smaller grows having a higher balanced irradiance is more important than spectrum. correct me if i'm wrong

If anyone has anything else to add please feel free.
 
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