nanometer/Kelvin What kind of bulb

Just my opinion.
The sun burns at 6500k...so a '6500k Day White Bulb' is the closest thing to sunlight...and what's better than the sun ? I've red lots of things about enhancing the fishes colour with this light and plants use this wavelength of light more etc etc but I've decided to just stick with normal 'Day Light' bulbs.

Also bulbs in the mid temperature range, around 6500, are slower to fade than the higher temperature bulbs.

You can’t convert directly between 1 wavelength and Kelvin temperature. Kelvin temperature is based on the spectra produced by 'black body radiators' basically think of this as hot metal without tinting by anything else other than the heat. It will never radiate at a single wavelength, if it did it would be a specific color and deviate from the spectra produced by a black body radiator, and couldn’t be considered a real Kelvin temperature rating. Actually fluorescent lights are usually rated in CCT or correlated color temperature, not true Kelvin temp, but close to Kelvin temp. A lot of manufacturers though simply call it color temp and its all labeled with the same Kelvin units anyway. If a single wavelength is given that usually means where the peak intensity is, not the overall color. 6500K would probably be the hottest the sun burns, more often I think its in the 4500-5500K range, but that’s just out of memory.

Usually the only bulb rating in nanometers are actinic bulbs. They represent light filtered by depths of water that attenuate longer wavelengths so all that is left is the blues, like 380nm-460nm for example.

Kelvin temp rating of a fluorescent bulb cannot tell you what the actual spectrum is in bulb. For example you can have a 'daylight' looking bulb that just has one big peak at around 580nm. Or one that has a gradual rise from 470 to 580 then back down to 700. Or it could have a peak in the low 500's and a peak in the high 600's and nothing at 580, yet it will look the same to us color-wise. It will look very different for plants though. This is why the K-rating isnt the perfect measure to go by.

Rule of thumb:

6500-6700K - good for plants
10K and up - reefs

Actinic (blue) - for people who want their reefs to look like they're under several more feet of water than they really are.

If you really want to complicate your life, start researching the CRI (color rendering index) of various bulbs too. 100 would be a perfect mimic of sunlight. Good plant bulbs get into the high 80-mid 90s range. Actinics are usually down in the 30s because they're designed to look like all but the blue area of the vis. spectrum has been filtered out by a couple fathoms of water.

Use any bulb that looks good to you.

There are some exceptions like full actinic lights and rare cases of inefficient tubes, but the vast majority of fluorescent lights will work just fine so it's up to your preference on how it looks.

The daylight 6,700k still looking kind of yellow to you? Try a 10,000k one.

Want to bring out the reds in plants and fishes? Try GE's 9,325k aquarays.

Actually enjoy a more yellowish light? Go with a 5,000k.

The Kelvin rating doesn't mean much if you supply enough wattage.

phanmc said:

Use any bulb that looks good to you.

There are some exceptions like full actinic lights and rare cases of inefficient tubes, but the vast majority of fluorescent lights will work just fine so it's up to your preference on how it looks.

The daylight 6,700k still looking kind of yellow to you? Try a 10,000k one.

Want to bring out the reds in plants and fishes? Try GE's 9,325k aquarays.

Actually enjoy a more yellowish light? Go with a 5,000k.

The Kelvin rating doesn't mean much if you supply enough wattage.

Click to expand...

phanmc - thats pretty much the realization I have come to also, that within reason just about any effecient bulb will work well. Some say thats true up to 10,000K, but after researching MH and realizing that there are 15,000K bulbs with more PAR and surprisingly more 'red spectrum' than lower K rated bulbs (even when compared to most higher wattage bulbs) I just finally determined that the K rating doesnt really mean squat.

Here is some interesting tidbits I have found. The 175W Iwasaki 15,000K has a higher PAR rating than a 400W(!) Coralvue 10,000K. Also the 15,000K versus a Giesmann 250W 10,000K. The Gies actually measures at 8420K and despite it being 43% higher wattage and much lower K value it has less 28% less PAR. Looking at the spectral graph here you can see the Iwasaki remains at or above the output of the Gies except for a few small peaks under 440nm (blue - actinic region) and 550nm and 575nm (green/yellow). But blue, blue-green, orange, and red the Iwasaki remains higher with less wattage.