[ChrisP]

OK, I know this is a really basic question, but comparing 150watt HQI lighting, aside from spectrum, is there a significant difference in light quality/intensity from one bulb to another?
Chris

[ejwsr]

The short answer is yes.

The long answer is that all forms of lighting have different efficiencies, spectral responses, radiance and luminance values. The problem is getting the data for an apples to apples comparison.

The medium answer is go with what you like looking at.

[pogodzib]

Each brand of bulb rates their k-value slightly different and the quality of the bulbs can very greatly. In general, the higher the k-value, the more blue and less intense it will be. A 6.5k bulb is yellow, 10k is white, 12k has a hint of blue, 20k very blue. Usually, people with lighting that is weaker will use lower k value bulbs to gain lighting intensity and coral growth rate. People with lots of lights over the tank don't need to worry about intensity as much so they choose a higher k bulb to give the tank a more blue look which helps to make the corals pop out. 10-12k bulbs are the most popular because the white/slightly blue hue and coral growth rate.