LED Lifespan and L70
L70 is the time until output falls to 70 percent of the original.
LEDs fade rather than burn out
A well-driven LED seldom stops suddenly. Its light output slowly falls over thousands of hours, so lifespan is stated as how long it takes to dim to a set fraction of its starting brightness.
What L70 means
L70 is the time for light output to fall to 70 percent of its initial level. A rating of L70 = 25,000 hours means it should still give 70 percent after that time under stated conditions. L50 uses 50 percent instead.
What shortens life
- High junction temperature, the biggest factor
- Driving above the rated current
- Poor heat sinking or enclosed fittings
- Voltage spikes and electrical stress
Making them last
Run the LED below maximum current, keep it cool and use a stable driver. At 25,000 hours, lighting for 4 hours a day would last over 17 years.
Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.