Quote Originally Posted by redline
So I might be better off running discrete royal, blue, cyan instead a cool whites of equal wattage ....because I won't have to take an efficiency hit from the phosphor coating ?
The problem is yellow and green leds have low efficiencies. As we require very little of it, aswell of cyan, the most profitable way of adding them is with white leds. Coolwhite leds have a huge peak around 450nm and then a continous spectrum peaking on yellow but that go beyond 700nm. So they complement very well with red leds, as gives the rest of wavelenghts and still some far red, wich its needed too. Coolwhite leds often have about 21% less efficiency than comparable Royal blues due to the change to longer wavelenghts at phosphors. But although it lower in that figure the energy efficiency, most of that drop happen on wavelengh conversion of photons, so they emits a very similar amount of photons than the Royal Blue inside it.

But today currently there is a way of giving that white light with a similar spectrum by using fluorescent tubes, at least from top ligting, wich is way cheaper. Using a Reflex tube with electronic ballast you get still higher energy efficiencies than a reflectorized HPS, and more than with white leds.

White leds emiting 150 lm/w are expected to be released in about 2 years (they are already developed in labs). By that time LEDs wont have alternative. But currently is reasonable to cut initial cost by giving the white light with fluorescent tubes or still with CFLs (for experimental purposes it dont mind if its slighty less efficient).

As red leds are cheaper, using a conventional white light and red leds is a cheap way to have good productivities on small gardens without investing huge money. And splitting the investment: now red leds and in two years, white ones.

There are Royal Blue LEDs very efficients, so they may be used together with white leds or white light in order to obtain the desired spectrum.

A very interesting page about optimal light spectrums for plants is this article: OPTIMIZATION OF LAMP SPECTRUM FOR VEGETABLE GROWTH.

We need to perform similar experiments with cannabis, but im working with the optimum RGB distribution of tomatoes as starting point (10-20%:15-20%:60-75%; B:G:R).

As coolwhite leds (aswell as daylight floros, with similar CCT ratings (6400K)) emits a bit more on the green than in the blue, but balanced, just adding to them red leds result on very well balanced spectrums.

For example, this is the result of 3 reds and 1 coolwhite all running at 350mA (CREES XR, white color WF (5700-6400K) and red R3 (625-630nm dominant), luminous bins Q4 and M):

[attachment=o206256]

It have a B:G:R distribution of 11:14:75% (R/B=7) wich seems pretty well balanced for flowering at medium-low irradiances.

The nice thing about leds is they are easily current adjustable, so we can modify the RGB distribution to adapt a given setup to different stages (veg, early bloom, late bloom) by modifying the current feed to each color. For example, with the same mix, if we put the white at 700mA but keep reds at 350mA, the spectrum is 14:19:67%.

Running all at 700mA results on 9.5:13.5:77% (both efficiencies and spectrum varies with current and temperature).

Options including Royal Blue are possible, especially when thinking on vegging lights, or using high irradiances along flowering. A mix 4R3+CW+RB result on this:

[attachment=o206257]

With a distribution of 29.5:9.5:61%.

Or, for example, 8R3+3CW+RB:

[attachment=o206258]

With a distribution of 22/14/64%.

Just a few samples of the spectrum you may create using red and white or red, white and blue.
knna Reviewed by knna on . Building LED lights from facts, no theories I was going to post this at the Perfect LED Grow Light thread, but as some of what im going to post was posted 2 years ago on the stickied thread about LEDs and people still continue developing lights from wrong ideas, i think a thread about this topic is largelly needed. The main problem is related to efficacy of spectrums. When the firsts LED experiments at Overgrow, we work on the hypothesis that blue and red light are more effective. It was an appealing hypothesis that promises large Rating: 5