Originally Posted by OverStocked
More often than not Co2 is no where near where you think it is. K rating is is related to visual spectrum and the actual output of the bulbs vary so much it is almost impossible to tell.
Lots of people grow great looking plants with bulbs with those K ratings... but since it is so subjective it means next to nothing.
OLD bulbs are often a problem too. Hard water causes more problems than most people think, too.
TOO MUCH light, Too LITTLE co2 and too little nutrients are usually the issue.
100% agreed with Overstock.
Nearly every "white" light that we might use will grow plants. The 6500K range is "optimal" but only critical if you are using a low light level, where every photon must count lol.
Nowadays with light sources as efficient as we have, you really don't have to fret it. As long as it's white (or even blue or red) it will grow plants as long it's not 100% blue or red. And even then, pure red or blue might grow a surprising number of plants.
I use a mixture of white, blue, and red LEDs (very few reds, they are overpowering if used too much). My tank's color temp is way way way cooler than 6500K. I have no way of measuring it but it's easily 10,000K or higher. Looks lovely and I can change the color temp with the twist of a dimmer knob.