On MH lights, what does "K" mean?

[civileng68]

What does the "K" mean in lighting (example: 10,000 K vs. 15,000K)?
Also,
I have a 55 gallon column tank (so it's deeper than a normal 55 gallon tank) and a 250 watt MH light.
However, I think it should have more light than that, so Im thinking of adding 150 more watts of MH lighting. does that sound pretty good?

 

[coachklm]

kelvins..... to the hman eye more kelvins is more blue/purple
just the colr/spectrum. not power

 

[sharkbait9]

for a better color example of the "k" rating to the human eye.

 

[fishieness]

however, just by how the make the bulbs, the higher the K, the lower the PAR. so the although the spectrum doesnt do anything as far as power, but bulb does. For example, a 6500K MH is a lot more powerful than a 20000K MH even if they are the same brand and watts.

 

[teen]

10k will look most yellow
20k will look most blue
i suggest 14k because its a good mix of yellow and blue and imo, it looks the best.

 

[wilsonreef]

ok, the last post did something wrong so here goes again. As in the chart above, the 6500k bulb is the most like the sun at noon. The 10000k is like the sky. I was running 6500k on my reef system for a while and then switched to 10000k. I can't see any difference. So what is the reasoning behind using one as opposed to the other? :thinking:

 

[viper_930]

The kelvin rating is the color. The number is not always perfectly accurate though, especially among different brands.

 

[moby]

Plus bulbs take a little time to "break in" so to speak. They start out looking different than after about 100 hours of running time.
Moby

 

[shrmnator]

i have found that 10000K is mostly white light, as opposed to 6500K.. at least thats what i see with my eyes.
the higher u get to 20000K, the more your corals will glow!! but the less they will grow!
i have Hamilton HQI 14000K bulbs