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I had the same results Jay and others noticed with different lights. We have to be careful however when we generalize by saying "Kelvin", I have a hunch spectrum has more to do with it than overall kelvin rating.

The GE 9325, which has a strong peak in red, seemed to me as the better light out of the ones I tried.

I think Phil has a great point, plants are not deep water species and there must be a mechanism for them to know when they are at the right depth. We all know that if lighting is insufficient the plants grow leggy and grow quickly towards the surface. I'm sure this occurs in nature as well when a plant is situated too deep, in this case the spectrum of the light it receives would be robbed of much of it's red. So perhaps the balance of red and blue in the spectrum is what tells a plant that it's at the right depth. If so, then a lot of red, such as these 9325K bulbs, could cause the opposite effect and trigger the plant to grow even denser than normal. Just a guess though...

Amount of light does play some role in it, mostly when the light is insufficient though. I have noticed better quality of growth in ludwigia repens in my 1wpg low light tank using the GE 9325K bulbs than my 4wpg using 10000K and 67000K bulbs.

I haven't noticed nutrient levels play a significant role in internodal length however, mostly color and health from what I could tell.

Giancarlo Podio
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