[munger]

One major thing no one ever seems to mention or realize about CFL bulbs is that if you read the fine print on the packaging, the life expectancy is based on leaving the bulb on for long periods of time like 3 hours per day continuous.

They have warnings along the lines of that damp environments like bathrooms, and turning them off quickly (less than 20-30 minutes on) significantly decreases the life of the bulb.

So if you plan to use CFLs that will be turned on and off quickly like bedrooms, bathrooms, hall lights, etc - basically everywhere except the living room / reading light that you plan to have on for hours at a time - CFLs will die faster than an incandescent - within 12-18 months of light use. You basically get punished for being good at turning off lights when not in use.

[hcarvalhoalves]

It's not only turning on/off that wears it out. CFLs lose efficiency over time anyway, down to 80-70% of the light output in as soon as 6 months. After a year or two they can be below 50%. Tri-phosphorous ones stay efficient for longer, but are harder to find, usually labeled for professional applications, and cost more.

If I'm not mistaken, LEDs being solid state don't lose efficiency over time like that, so it's always working at peak output as long as the driver lasts. That alone should make it more cost effective.

[tanzam75]

No. In fact, the LED lifetime stated on the packaging is actually the time it takes to decrease in brightness to a specified reference level -- usually 70% of initial brightness.

Since it is solid-state, though, the LED is expected to continue operating long after it reaches 70% brightness. 70% is simply the assumed reference point at which the consumer becomes annoyed and decides to replace the LED.

Source: Department of Energy, "Lifetime of White LEDs", http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl...

> the Alliance for Solid State Illumination Systems and Technologies (ASSIST), a group led by the Lighting Research Center (LRC), recommends defining useful life as the point at which light output has declined to 70% of initial lumens (abbreviated as L70) for general lighting and 50% (L50) for LEDs used for decorative purposes.

[hcarvalhoalves]

Even the new generation LED lamps are like that (Cree X and such)? I read something the other day that suggested these LEDs were immune to losing efficiency over time (the efficiency would be dictated only by heat).

[tanzam75]

Yes, LEDs will last longer without heat issues. But unless you're running the LED in a refrigerator, that's not a particularly informative statement.

As stated in the DOE that I linked to: "The primary cause of LED lumen depreciation is heat generated at the LED junction." Because it's the primary cause, you can't just ignore it and say that LEDs barely degrade in the absence of heat. You have to consider the heat when calculating LED lifetime.

The stated lifetime on the LED packaging makes a number of assumptions, one of which is that the LED is run at room temperature.

[ars]

> If I'm not mistaken, LEDs being solid state don't lose efficiency over time

You are mistaken, LEDs most definitely do lose efficiency.

http://web.archive.org/web/20090410145015/http://www1.eere.e...

LEDs and CFLs are about the same as far as losing efficiency.

[coin]

Is it the phosphors that wear out? If so, many LED bulbs uses phosphors, make it also a form of fluorescence bulb.

[hcarvalhoalves]

The CFL works by exciting the mercury vapor in the tube to give off UV, which then strikes the phosphor coating, emitting light in the visible spectrum. This UV radiation wears the coating over time.

I'm not aware of the design of these LED bulbs you mention, but they might work under the same principles, the LED just replaces the mercury as the UV source.