Originally Posted by It's 5 o'clock somewhere

Actually, not true. It's the way the light makes the light that produces the heat. The 150w cfl isn't actually working on 150w. It just gives out the same lumes per square inch as a 150w bulb. The Hps needs a ballast that is powerful enough to cause the bulb to arch across the gas in the bulb. The cfl doesn't need as much electricity and it's starter is located in the base of the bulb. Cfl's run cool enough to have within inches of your plants but they also lack the strength of the HPS to push it's usable light energy deep into the plant. But with the ability to get so close to the plant it allows you to use them in places that you can't put an HPS light like under the plants shining up into the lower parts of the plant.