Drivers usually die before the LEDs — the weak point is the electrolytic capacitor and heat. How to read the tc point, the temperature/lifetime relationship, five heat sources, and an eleven-point cooling checklist.
When a fitting starts flickering after two years, most people suspect the LED first. In practice the driver usually fails before the LEDs, and inside the driver the first thing to age is the electrolytic capacitor. This guide covers how temperature eats lifetime, and eleven things you can do about it on site.
The short version: the capacitor is the weak link, and heat is what kills it
LED packages last a long time (25,000–50,000 hours is typical, judged on lumen maintenance). Inside the driver, the electrolytic capacitor loses electrolyte faster as temperature rises: capacitance falls, ESR rises, and the symptoms are larger output ripple, unreliable starting and intermittent protection trips.
That is why driver lifetime is quoted in this form:
50,000 h @ tc 75 °C
It means 50,000 hours expected life provided the case temperature at the tc point stays at or below 75 °C. It is not a promise that applies however you mount it — it is a promise conditional on temperature.
Temperature and lifetime
The common engineering rule of thumb: every 10 °C rise at the tc point roughly halves electrolytic capacitor life (and the reverse: 10 °C cooler roughly doubles it).
Measured tc
Relative life (nominal condition = 1)
What it means on site
20 °C below nominal
about 4×
Well ventilated with power headroom
10 °C below nominal
about 2×
Typical once proper margin is left
At nominal
1×
Exactly the manufacturer's stated condition
10 °C above nominal
about 0.5×
Sealed light boxes and summer rooftops
20 °C above nominal
about 0.25×
Failures start within two or three years
This is an engineering rule of thumb, not a precise physical law. Real life depends on the capacitor series, ripple current, duty cycle and actual cooling. As a conservative estimate for selection it is the right tool.
Life versus temperature: horizontal axis is the difference from nominal tc, vertical axis is relative life
Five heat sources
Its own losses — an 88%-efficient driver on a 100 W load turns about 12 W into heat. A 3–5 point efficiency difference is a real difference in heat
Hot ambient — rooftops, west-facing walls and light boxes can sit 20–30 °C above outdoor air
Sealed spaces — ceiling voids, plasterboard cavities and small metal boxes simply have no convection
Stacked units — several drivers mounted together heat each other; the middle one fails first
Non-conductive mounting — fixing to wood, plasterboard or plastic trunking cuts the heat path
Eleven things to do on site, best value first
Leave 20% wattage headroom — continuous full load is the main driver of temperature rise, and this pays back the most
Mount on metal — a metal surface is a free heat sink and beats wood or plasterboard by a wide margin
Leave spacing — at least 5 cm between units; never stack them
Avoid small sealed boxes — if unavoidable, fit louvres or use a larger enclosure
Keep away from other heat sources — not against transformers, ballasts or hot water pipes
Mount in the orientation the datasheet specifies
Avoid direct sun on roofs and west elevations — a shade plate costs far less than a replacement driver
Keep vents clear — a blocked filter is the same as no vent
Check the input voltage — running continuously high increases losses
Do not put the driver inside the luminaire cavity — LEDs and driver cook each other
Re-check case temperature after year one — a rise means the cooling conditions have changed
How to tell a driver is already running too hot
Symptom
Meaning
Action
Case too hot to hold (roughly 70 °C and up)
tc at or beyond nominal
Improve cooling or upsize
Runs, then drops out after an hour, restarts when cool
Thermal protection cycling
Deal with it now — do not live with restarts
Burnt smell or discoloured housing
Close to failure
Replace immediately and find the cause
Larger output ripple, slight shimmer
Capacitor aged
Plan a replacement
The unit in the corner of a batch fails first
Worst cooling position
Fix the location before the part
The one line to act on: dropping 10 °C beats adding 20% wattage headroom. When specifying, ask "at what tc is that lifetime quoted" rather than "how many hours" — the latter means nothing without the temperature condition.
Need a lifetime that matches your site? Tell us the mounting environment, how sealed it is and the daily burning hours — we will pick models with enough case-temperature margin. Contact →