at the base of the bulb where it plugs into the fixture it will have four pins.
They come in flat pin configuration
And square pin configuration
[hr]
On your bulb, If it is one side white/one side blue then it is a 50/50 bulb.
50% Actinic
50% 10,000k
You can go with any combination of colors.
* full 10k =brightest output but colors in your tank tend to appear washed out and bland.
* 12k =the small move towards the blue side of spectrum keeps the brightness, but highlights a hint of color in tank.
* 14k =again a step towards more blue, brighter colors but visual light will not be so bright to the eye. (most common choice for full color and yet staying brightly lit)
* 20k =jumping to 20k will yeild extreme highlights and show off the colors, but buld will seem dim to your eye.
* Full Actinic = Light will make dramatic change in colors and cause pigments in your livestock to floures brightly. Tank will look odd to the eye with almost funhouse effect without addittional "brighter lighting"
*50/50 For obvious reasons mentioned above its a combination bulb to try and get best of both worlds.
from brand to brand you can expect slight differences in what the company deems to label one bulb 12k where another says its 14k.
Name brand compared to cheapo should provide more longevity and closer to spec for true output in color posted.
match your pin configuration and the wattage is 96w. (common bulb) then go to town!!!
If your fixture take multiple bulbs, the color spectrums are completly up to you. Just match the size and wattage with the pin configuration required.
Hope this helps
-RFB