Understanding Light Ratings
One of the main reasons for using fluorescent lights is high efficiency. Fluorescents vary tremendously, however, with some not much better than incandescent. There is much confusion regarding this, and unfortunately manufacturers only make matters worse. In order to make an informed choice, we need a basic understanding of light ratings. In advertisements we see statements like "equal to 50-watt bulb," "400 lumens," "25% more light than 25-watt bulb," etc. More often than not, these statements are inflated by up to 200%! How does that happen? As you may know, a 12-volt bulb rated at 15 watts uses 1.25 amps (volts x amps = watts). Amps and light output of incandescent lights can be predicted just by knowing the wattage of the bulb. This simple relationship doesn't occur with fluorescent lights, however. The light output of the bulb is controlled by the ballast.
The 8-watt tube used in most conventional marine fluorescent lights can be supplied with less than 8 watts, in which case the light output will be correspondingly less. Some companies do this, but still claim the light output of a fully powered tube even though it's much less. A standard 8-watt fluorescent tube produces about 50 lumens per watt (the compact fluorescent tubes used in Alpenglow lights give 65 lumens per watt). No electronic magic can significantly change that. In addition, all ballasts consume some power, generally 15% to 25%. Therefore a light advertised as using .4 amp (4.8 watts) uses at least .8 watts for the ballast, leaving 4 watts for the bulb. So it isn't an 8-watt light at all. It's a 4-watt light and there's no way that it can give more than 200 lumens. This is an actual example, and that particular light is advertised as an 8-watt light with an output of 400 lumens. Tests show that it is about 200 lumens and power used is .52 amp. So it gives 1/2 the light output and uses 30% more power than claimed. This is not an extreme example. There are some better and some worse. One light is claimed to be 25% brighter than a 25 watt bulb. All we can say is, get one and try it. You will find that it is about half as bright.