LM-85 is an Illuminating Engineering Society (IES) approved method for the Electrical and Photometric Measurements of High Power LEDs. The Commission Internationale de L’Eclairage (CIE) has a similar method named TC2-063. LM-85 focuses on the special needs related to getting light measurements for high power LEDs that require heat sinks for their normal operation. White LEDs, UV LEDs and single color LEDs are included.
There are several methods for taking LM-85 Light Measurements for High Power LEDs.
- DC
- Single Pulse
- Continuous Pulse
- LM-92 released in 2022 defines several additional mehods including the DCP (Differential Continuous Pulse) method. LM-92 measurements are required for UV LEDs.
All methods including DC require pulsed current drive to the LED under test. Typical pulse specifications for each method might be:
| Method | Typical Pulse Width | Needed Rise Time | Delivered Power |
|---|---|---|---|
| 1. DC | Step change | <10μS | Continuous |
| 2. Single Pulse | 10-500mS | <100μS | Long duration |
| 3. Continuous Pulse | 50-200μS | <10μS | Short duration |
| 4. Differential Continuous Pulse | 10μs-20μs | <10μs | Short-pulse |
These parameters place high-performance demands on the current source. The two key current source specifications are rise time and the continuous available power. Popular source meter instruments sometimes deliver high peak power levels, but only for short durations. They also lack the fast rise times necessary for the DC and Continuous Pulse methods. These limitations mean source-meters are only appropriate with the Single Pulse method, and only when the LED under test is below the source-meter’s continuous power rating.
The SpikeSafe Source Measure Unit (SMU) produces accurate optical measurements for all LM-85 and LM-92 methods. The SMU has no power limitations, rise times in the ns range, and short pulse widths.
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