Color Temperature

[DavidCampen]

CRI has nothing to do with how effective the light is for plant growth and flowering. CRI is just an attempt to assign a number to how effective the light is at rendering colors. A mixture of red and blue light from LEDs is very effective for plant growth and flowering yet it would have a very low CRI value, while incandescent light has a CRI of 100.

[Ray]

David is right. CRI is only of aesthetic value to you.

[alley]

Hey guys, I just purchased a 2ft fixture with 4 T5's...but I've noticed all the posts say 4ft.(after I bought the fixture of course) Have I really screwed up? or can I use this fixture effectively for 4 phals? Thanks...

[Ray]

Sure, why not? You simply don't have the same wattage, so cannot light up as big of an area.

[alley]

Originally Posted by Ray

Sure, why not? You simply don't have the same wattage, so cannot light up as big of an area.

Thanks Ray, I appreciate it. I can always buy more light later on if necessary, I was concerned about something I had read about lumens in another thread...

[tropterrarium]

OK, jumping in once more. I get the idea of matching lighting to PAR and that's all that is need to grow plants. This is the reductionist way of thinking. I am more of a holistic biologist. Plants have evolved to use sunlight, the entire spectrum, some modified by geography and habitat, fair enough. To think that plants are ideally served with narrow spectra and light significantly different from sunlight may also think that one can nourish the human body with protein shakes and vitamin tablets alone. Both may be able to survive, but it ain't a happy existence. One could call it actually abusive culture, in the same sense as it is problematic to keep a single dog (dogs are group animals, some countries now have laws that prescribe that one has to keep more than one dog).

Just because we know the absorption spectrum of Chla and b, does not mean that we know what else light is doing and what the rest of the spectrum is good for. For instance the role of Pr and Pfr for circadian rhythm, but I digress.

Back to the CRI. IF one subscribes to the idea of providing an as close to natural condition as possible to the plants, then the CRI is meaningful.

The statement of an incandescent bulb having a CRI of 100 is sort of true, sort of misleading. Because a glowing tungsten wire is a blackbody radiator like the sun, it has the spectral distribution of a blackbody radiator. BUT an incandescent bulb has a color temperature of ~2,200K, whereas standard daylight is in the 5,000-6000K range. So if you compare the CRI of 5000K daylight to an incandescent bulb at 2,200K, the CRI would be very poor, guestimated at 10-20, possibly even lower.

Last but not least, I like to look at my plants. Strange concept, indeed. Ever noticed that colors under regular fluorescent light look off? That is because the CRI of those Home depot/Lowe's bulbs is rather poor, in the CRI 60 range. If you like color how it really looks like, then possibly invest into full spectrum lights.

[Ray]

Good post, Trop.

As an example, I was reading recently of how carotenoids also contribute to the plant by absorbing light - in different parts of the spectrum than do chlorophylls - and passing the energy onto the chlorophyll for greater efficiency.

[tropterrarium]

Yep, so called antenna pigments in the electron transport chain. But then there is so much more we don't have the foggiest about, particularly me, with a C- in advanced plant physiology ;-) Thought the courses were just too boring.

I forgot to mention that some people don't see the difference in color rendition between different bulbs. I am very picky about color, as I'm a photographer. I go the whole way from a Minolta Color Meter III, to spider calibrated monitor, to fully profiled printer. You can train your color perception, similarly as you can train your taste buds.

[DavidCampen]

Originally Posted by tropterrarium

The statement of an incandescent bulb having a CRI of 100 is sort of true, sort of misleading. Because a glowing tungsten wire is a blackbody radiator like the sun, it has the spectral distribution of a blackbody radiator. BUT an incandescent bulb has a color temperature of ~2,200K, whereas standard daylight is in the 5,000-6000K range. So if you compare the CRI of 5000K daylight to an incandescent bulb at 2,200K, the CRI would be very poor, guestimated at 10-20, possibly even lower.

No, by definition a tungsten bulb has a CRI of 100.

Color rendering index - Wikipedia, the free encyclopedia

[Exo]

Question.....I have a T5 HO fixture with 8 bulbs...4 are 3000k....and 4 are 6500k. I did this to have an even balance for growth and flowering, since I had heard that 3000k are better for flowering, and 6500k are better for plant foliage growth.

But if what I'm seeing here is true.....what I heard is false, and 6500k bulbs are better than 3000k for flowering.

Am I hearing this right?...if so, why do they sell 3000k bulbs for this?