3k. CFL Analysis - Light Reduction

Unlike halogen and most incandescent lamps, all fluorescent and HID lamps lose output with age; some more than others, especially covered and reflector CFLs. 10% after 1000 hours for bare tubes and more and as they age, is considered normal in the lighting industry. Though the general public is usually not informed of this fact and will end up with less light than they thought they were buying if they follow the recommended conversion charts.

U.S. Department of Energy tested ENERGY STAR-labeled lamps and found that:

"In Cycle Four, 38% CFL samples failed to meet the requirement of lumen maintenance at 40% rated life, and the majority of covered lamps and reflector lamps failed this requirement with the exception of two models from a certain manufacturer." [1]

In a 2008 Swedish consumer test, Philips, Osram and IKEAs bare tubes had lost a mean of 19% after 6000 hrs, Philips & Osram covered bulbs a mean of 25%, and Ikea bulbs 30-100% (= some didn't last long enough to measure). [2]

And these are some of the best CFLs on the market. Lower end lamps can be expected to lose even more.

1. Energy Star Lighting Verification Program
2. Råd & Rön 1/2008

Update Dec 2: Finally, some journalists are starting to actually read consumer and governmental tests instead of just mindlessly trusting the inflated propaganda from EU, Energy Star and Energy Saving Trust.

Energy saving light bulbs get dimmer over time

Just as I've been saying. Every lighting professional knows this and plans for it. And you don't even have to check consumer tests: it's right there in manufacturer catalogues (if you know what you're looking for) and manufacturers won't deny it if asked; they're just not going to volunteer that information to the public if you don't ask.