What the number is
LED lifetime is usually quoted as the time to 50 percent of initial luminance at a given drive current and temperature. It is not a failure point. The screen still works at 50 percent; it just looks tired. Some manufacturers quote L70 (70 percent), which is more useful, and some quote L50 because it is a bigger number.
Why temperature dominates
The same LED driven at 25 degrees junction temperature and at 75 degrees has a lifetime difference of roughly four times. This is why an outdoor screen running at high brightness in a hot climate ages faster than the datasheet suggests, and why the thermal design matters more than the LED brand.
A realistic decay curve
| Year | Indoor, 600 nits, 8h/day | Outdoor, 6000 nits, 16h/day |
|---|---|---|
| 1 | 97% | 93% |
| 3 | 91% | 82% |
| 5 | 85% | 71% |
| 8 | 76% | 58% |
What it means for design
If you specify 5000 nits for an outdoor wall and it will sit at 60 percent in year five, you have 3000 nits on the fifth summer day. That may still be enough. If you specify 5000 nits because you needed 4800 on day one, you will be disappointed. Buy headroom, or plan a brightness re-calibration in year three.
What actually fails first
Not the LEDs. In our service data, the first failures are power supplies, then receiving cards, then fans. LED modules usually outlive the electronics around them. That is why spare parts planning should focus on power supplies and cards, not on a shelf full of modules.
The maintenance question to ask
Ask for a brightness measurement protocol so you can track decay objectively. A cheap lux meter at a fixed point, measured every six months, tells you more than any warranty clause. When output drops below the level the content needs, that is your real replacement date, not the hour count.