when 6500k is not 6500k...

[Plantcrazed101]

On one of the forums, Ray mentioned (if I'm understanding this right? Please correct if I'm wrong as I'm eager to learn!!!) that the color temperature specified for black body radiator type lights are not necessarily the exact same wavelengths for LEDs or CFLs with correlated color temperature names. In other words, a 4100k HPS and a 4100k LED are not the same light wavelengths, they just appear similar to the human eye and so are called the same. That means there is room for error on what our plants are actually getting.

I think I saw that this answer from Ray was from 2005, so I'm wondering if y'all (or Ray if you see this) have any thoughts or comments as to what would be the best color temperature for LEDs or CFLs?

Originally Posted by Ray

Color temperature is a way of describing the spectrum, and yes, something in the neighborhood of a 6000°K color temperature is ideal for plants, as it comes close to replicating the light provided by the noontime sun plus the blue back-scatter from a clear sky - the light all plants get.

However, as neither LEDs nor fluorescents are black body radiators (incandescents and HID lights are), the color temperature specified for them is a correlated, or corrected color temperature (CCT). That is, it is the correlation of how that light looks to the human eye, when compared to a black body radiator, and NOT the same spectrum as one.

I really have no idea what the "ideal" red/blue mix is, but for what it's worth, the 35W Philips "Production modules" I am using in my "basement incubator" have 68 reds and 24 blues per strip. Their "flowering lamps" on the other hand, have a much higher red:blue ratio.