Why LED bulbs fail early — and how to make yours last

The promise is 25,000 hours. The complaint we hear most often is a lamp that lasted eighteen months. Both can be true at once, and the gap between them is almost never the diode. This is what our returns analysis actually finds when we take failed lamps apart, in order of frequency.

What is inside an LED lamp

An LED lamp is four components in a bulb-shaped housing, and only one of them is the light source.

• The LED package — one or several semiconductor dies on a board, with a phosphor layer to convert blue to white. This is the part rated for 25,000 to 50,000 hours.
• The driver — a small switched-mode power supply converting mains AC to the low-voltage constant current the diodes need. This is where nearly all sudden failures happen.
• The heat sink — aluminium, ceramic or filled plastic, conducting heat away from the LED board. Its adequacy determines how fast the diodes and phosphor degrade.
• The optic — diffuser or lens, shaping the output.

The consequence is that an LED lamp’s real lifetime is the lifetime of its weakest component, and that is almost always the driver. A lamp with excellent diodes and a cheap driver is a cheap lamp.

Cause 1: heat, which is most of the story

LEDs do not radiate their waste heat forward the way an incandescent does. They conduct it backwards into the base. Junction temperature is therefore the single variable that governs how quickly a lamp degrades, and every other cause on this list is really a way of raising it.

The relationship is steep. As a rough guide, every 10 °C rise in junction temperature roughly halves useful life. A lamp rated L70 at 25,000 hours with a junction at 85 °C may reach L70 in 12,000 hours at 95 °C and 6,000 at 105 °C. Heat also accelerates phosphor degradation, which is why old LED lamps often drift bluer as well as dimmer.

What raises junction temperature:

• An undersized heat sink. The most common economy in a cheap lamp: plastic that looks like finned aluminium.
• High ambient temperature. A ceiling void in an uninsulated roof can reach 50 °C in summer before the lamp adds anything.
• Base-up orientation. Heat rises into the base rather than away from it. Some lamps are rated for base-down operation only; check before fitting them in a ceiling.
• Overdriving. Running a given LED package harder to hit a lumen figure with fewer diodes. Cheaper to build, hotter to run.

Cause 2: enclosed fittings

This deserves its own heading because it is the most common installation error and the easiest to avoid.

A sealed globe, a flush ceiling fitting with a glass dish, an outdoor lantern with a closed body — all of these trap the air around the lamp. A lamp that runs at a 70 °C case temperature in open air may run at 100 °C in the same fitting enclosed. That is not a marginal difference; it is a lamp lasting a quarter as long.

Manufacturers respond by testing and rating lamps for enclosed use, which means a larger heat sink, driver components specified for higher temperature, and often a slightly derated output. The rating is printed on the carton and in the specification sheet. Lamps without it usually carry an explicit warning against enclosed use, in small type, which nobody reads.

Cause 3: the driver, and the electrolytic capacitor

When an LED lamp dies abruptly — works one evening, does nothing the next — it is nearly always the driver, and within the driver it is nearly always an electrolytic capacitor.

Electrolytic capacitors use a liquid electrolyte that dries out over time. The rate depends on temperature, and it follows the same brutal arithmetic: capacitor life roughly halves for every 10 °C. A capacitor rated 2,000 hours at 105 °C gives 8,000 hours at 85 °C and 32,000 at 65 °C. Fit that capacitor into a hot lamp base and the 25,000-hour diodes become irrelevant.

This is the main thing that separates a $2 lamp from a $6 one, and it is invisible on the shelf. Better lamps use capacitors with higher temperature ratings and longer endurance hours, or avoid electrolytics entirely in favour of ceramic or film types in a design that tolerates the lower capacitance. They also place the driver where the LED board’s heat is not conducted straight into it.

You cannot inspect for this. What you can do is treat an unusually low price as information, and buy from someone who will replace the lamp when it fails — which is the entire argument for a registered warranty rather than a receipt in a drawer.

Cause 4: the electrical environment

Four electrical conditions shorten LED life, and three of them are fixable.

Voltage transients

Surges from grid switching, nearby lightning and large motors starting stress driver components. LED drivers typically survive a few hundred volts of transient; a nearby strike can deliver thousands. Whole-house surge protection at the panel is cheap relative to a house full of failed electronics, and it protects more than the lighting.

Sustained over-voltage

Nominal 120 V supplies routinely sit at 125 V, and some run higher. Drivers are designed for a range, but the top of the range is not where they are happiest. If a whole building is losing lamps unusually fast, measure the supply voltage before blaming the lamps.

Incompatible dimmers

A leading-edge dimmer chops the AC waveform in a way an LED driver was not designed to see. The result is flicker, buzzing, premature driver failure, or all three. This is common enough to have its own article.

Shared neutrals and switch-leg capacitance

A lamp that glows faintly when switched off is picking up a few milliamps through capacitive coupling in the wiring, or through a neon-indicator switch. It is usually harmless but it runs the driver continuously at very low current, and it is an easy fix — a small bypass capacitor at the fitting, or replacing the indicator switch.

Cause 5: binning, and what “same model” means

LEDs come off the line with a spread of brightness, forward voltage and colour. Manufacturers sort them into bins and sell the bins at different prices. A lamp built from the edge of a wide bin is within specification and visibly different from its sibling.

This does not usually cause failure, but it causes something people experience as failure: a row of downlights where one is noticeably dimmer or pinker than the rest, or a replacement that never quite matches. When a customer says a lamp “went wrong”, they sometimes mean it never matched in the first place.

Ask for the SDCM figure — 3-step or better for general use, 2-step where lamps sit side by side — and order all the lamps for one space at the same time.

Nine things that actually extend lamp life

1. Buy enclosure-rated lamps for enclosed fittings. The single highest-value action on this list.
2. Give the base air. Do not pack insulation against a recessed can unless the can is IC-rated for it.
3. Respect orientation ratings. If a lamp says base-down only, base-up will cost you years.
4. Match dimmer to driver. Trailing-edge, LED-rated, with a minimum load below your actual load.
5. Fit surge protection at the consumer unit or panel.
6. Do not over-tighten. Screwing a lamp in hard can crack the solder joints inside the base. Finger-tight plus a few degrees.
7. Keep the heat sink clean. Dust is an insulator. In kitchens and workshops, wipe the fins occasionally.
8. Buy for the room, not the price. A lamp specified for its actual duty cycle outlives two cheap ones.
9. Register the warranty. It converts a lottery into a guarantee, and it takes two minutes.

Common questions