Mixing Kelvin ratings.

I mix 6700K and 10000K for a nice overall color. It works great. Anything in the 5100K - ~12,000K range is OK for plants.

Kelvin ratings wont effect each other - its not going to like cancel each other out as far as the plants are concerned. There has and is a lot of debate on whats the best for plants. The thing is the way the Kelvin is rated, its not the best rating to go by. Two bulbs with the same K rating can have different spectral peaks. Plants 'see' the wavelenght of light not the K rating... and althought the wavelengths have a lot to do with the K rating in an ideal lightsource, fluorescent bulbs dont produce light true to the K rating but rather they use a 'Correlated Color Temperature'. Sometimes I wonder wether they are actually based off the overal color or just where the largest spectral spike occurs.

Some say trying to figure out whats best is pointless, better of just getting light thats more appealing to you to look at, just make sure its bright enough, and the plants will use it. Ideally plants can utilize red and blue wavelengths, so if you want to try and get the best lights look for spectral radiance charts often found on most packaging for bulbs, and look for peaks near red/orange and blue.

Here is a few pics I have posted before on discussions about lights:



Edit: note that if you search google for something like "photosynthesis spectrum chlorophyll" you can learn all about how plants absorb light... and the light's K-rating is hardly ever even mentioned.

thefirethief said:

I'll make sense of your pics soon .

Click to expand...

No problem. Trying to figure it all out is definately a challenge. Instead of being concerned with K rating, I have seen references to a PAR rating (photosynthetically active radiation) which seems like it would be a good rating to go by, but most manufacturers are not rating this.

The key point I was making with the pictures is: look at the top picture, you'll see a grey line with a spike in the blue range around ~460nm. Youll also see a spike in the red range of around ~670nm. Those spikes are chlorophyll's maximum absorption. And as such many people have beleived that is the only important light, and that light in the green spectrum for example is not used at all. But on the same graph look at the green line which is the measeured rate of photosynthesis. Although it peaks very similar to chlorophyll, it has a much broader range due to the fact there are more things than just chlorophyll that absorb light to help the plants photosynthesize.

FWIW the main difference between full spectrum/daylight bulbs and a specific plant bulb is that daylight bulbs typically have their strongest peak in green which is least usefull for plants, but makes the bulb look whiter and brighter to our eyes (human sight is most sensative to the green range), but plant only lights usually just have blues and reds and very little green. As such they dont look as bright, and are not as white. So far my favorite plant-only bulb (I mix plant bulbs and daylight bulbs) is the T6 Aqua-Flora plus (by quantum aquatics) which has a strong spike near red/orange, a very small spike at yellow/green, and a hump through all of blue with a small spike in the middle. The actually color of the bulb is a bluish-purple which I think adds a nice effect similar to actinic blue, rather than the funny pinks and other colors other plant lights produce.

Good luck with your plants.