what does 450nm mean on bulbs?

[bnhd3]

i have a light that i had made for me. it has 2 250 metal halides and 4 96 450nm bulbs. what is the difference between an actinic a 10000k, 15000k, and a 450nm.? what does nm stand for and what does k stand for? also maybe some recommendations on which is better for a reef tank?:bum: http://reefcentral.com/gallery/data/500/139904week_5_125g_tank_003_mini.jpg

[papagimp]

the number relate to the particular color spectrum of that bulb. 450 is an actinic bulb, I think it's the more blue one, where the 420nm is more purplish, or vise versa, I forget. For instance, on my freshwater tank, I use a 6500k bulb since it replicates more of a yellow light that the plants need for growth and photosynthesis. While in my reef tank, I use a 10000k bulb for more white lighting and better coloration. (I actually use more than just that, but you get the idea)

For a reeftank, theres a lot of variables to consider as far as what type of livestock you have. Since your lights have the MH's on them, I would stick with either two or four of the Actinic bulbs (blue spectrum) for the power compacts.

I forget what the "k" stands for, kelvin or something.

[boomsticks]

K does stand for kelvin its a unit of light temperature (color)

[sir_dudeguy]

450 is just the color or wavelenght or whatever they're measured in. 420 would be a true actinic (purpleish bulb) and 450 would be a bluer bulb (tho i did not know they made 450's...i do have 460's tho...very blue and pretty bright)

[brward5]

... and nm stands for nanometer, it's the wavelength of the light produced.
~Brian