How long LED bulbs actually last

A rated life of 25,000 hours is not a burnout date. It is a lumen maintenance figure, and ENERGY STAR's specification defines it precisely: the elapsed operating time over which the LED light source will maintain a percentage of its initial light output - L70 being the time to 70 percent lumen maintenance.

There is a second letter that rarely makes the box. The DOE explains that because failures across a set of installed lamps do not all happen at once, lumen maintenance ratings are usually established at the time when 50 percent of a sample is expected to reach L70 - written L70-B50.

Read together: at the rated hour, half the sample is expected to have faded to 70 percent of where it started. Some bulbs will be better, some worse, and none of them is promised to still be lit.

Heat, first and always. ENERGY STAR states that thermal management is generally the single most important factor in the successful performance of an LED over its lifetime. That is why an unrated bulb in a sealed globe fails years early while the identical bulb in an open lamp does not - and why the enclosed rating is worth paying for. The options are in best LED bulbs for enclosed fixtures.

The driver, second. The DOE says plainly that the driver is the weak link for some currently available LED products. The LEDs may be fine; the small power supply behind them is what quits, which is why a bulb can go from working to dead with no fading at all.

Infant mortality, third. The DOE attributes early failure primarily to material and manufacturing defects. A bulb that fails in the first weeks is a warranty claim, not bad luck you should absorb.

And switching, in some fixtures. A bulb in a closet or a bathroom that is cycled dozens of times a day lives a different life from one in a hallway left on all evening.

Warranty terms are much shorter than rated lives, and they cover defects rather than fade. Three real examples, quoted from the makers:

Cree Lighting publishes a USA limited 10-year warranty for its LED bulbs - but only 3 years for its 4Flow filament design, and states that replacement or refund is its sole warranty obligation.

LEDVANCE, for SYLVANIA general purpose LED lamps, publishes 36 months at up to 4,380 hours per year, and says that if the product is operated more than 4,380 hours a year - 12 hours a day - the warranty period drops to 12 months. It also conditions the warranty on the product being used in lighting equipment designed and approved for the application.

Feit Electric publishes a five-year term on its Costco range, again with replacement or refund as the sole remedy.

ENERGY STAR ties the two ideas together in its own specification: lamps rated under 15,000 hours need a minimum two-year warranty, and those at 15,000 or above need three - calculated at three hours of use per day.

Prefer bulbs whose makers publish terms. The Sunco BR30 publishes a five-year warranty and a 25,000-hour life on the same page, which is what a claim needs. The Feit selectable A19 and Philips A19 are similarly documented.

Keep the receipt with the pack. Every warranty quoted above runs from the date of purchase, and the remedy is replacement or refund - both of which need proof.

Match the bulb to the fixture, because warranties say so. Sylvania's terms require the product to be used in equipment designed and approved for the application. An unrated bulb in an enclosed fixture is both a shorter life and a weaker claim.

Do the running-cost math separately. Life and energy are different questions, and the money is usually in the second one - see what it costs to run your lights.