L70 Lifetime Calculator

TM-21 lumen maintenance projection from LM-80 test data — predicts L70, L80, and L90 lifetimes

Test Conditions

LM-80 Test Temperature

Drive Current (mA)

Initial Lumens (at t=0)

In-Situ Temperature (degrees C)

Actual LED junction temp in your fixture

Reporting Multiplier (TM-21)

LM-80 Lumen Maintenance Data Points

Enter measured lumen maintenance (%) at each test interval. Minimum 3 points required.

Load preset:

Hours (h)

Lumen Maint. (%)

—

L90 Lifetime (h)

—

L80 Lifetime (h)

—

L70 Lifetime (h)

—

L50 Lifetime (h)

Lumen Maintenance Projection

TM-21 Fit Parameters

Notes

Practical Notes

L70 is the time at which an LED has dimmed to 70 percent of its initial light output, and it is a common way to describe the useful life of an LED. L80 and L90 are the times for 80 and 90 percent. LEDs do not burn out suddenly like old lamps but fade slowly, and these numbers say how long until the fading becomes noticeable.

The calculator uses the method in the TM-21 standard, which projects lumen maintenance from LM-80 test data. LM-80 measures the output of LEDs over at least 6,000 hours at several temperatures, and TM-21 extends the results, but only up to six times the length of the test. A 10,000 hour test can support a projection of up to 60,000 hours.

Heat is the main thing that shortens LED life, so the temperature at which the LED runs strongly affects the result. These figures describe the LED package and not the complete fixture, whose driver and other parts may fail earlier, so look at the warranty and the fixture test data as well.