The total luminous flux (lumen) is one of the most important characteristics of Light Emitting Diodes (LEDs), and is commonly measured using integrating sphere photometers. Large variations of measurement results are reported among different manufacturers and users of LEDs. There are issues such as the LED mounting geometry (4p, 2p), treatment of backward emission, the best integrating sphere geometries, etc. While these issues remain to be resolved, there is an urgent need for reference LEDs in order to certify measurement accuracy in industrial laboratories. To address such needs, NIST has developed measurement procedures to calibrate the total luminous flux of LEDs using the existing NIST 2.5 m integrating sphere. The arrangement for the NIST integrating sphere is for integration over 4p. In spite of the size of the sphere, the signal for typical high-intensity LEDs having total luminous flux of 0.1 lm to 1 lm is large enough for an accurate determination, in part to the high reflectance (~98 %) of the coating. The calibration service for LED total luminous flux is now available at NIST. The expanded uncertainty (k=2) of the calibration typically ranges from 0.6 % to 2.3 % depending on the color and other characteristics of the submitted reference LEDs.
Conference Dates: July 9-11, 2001
Conference Title: International Conference on Compound Semiconductors
Pub Type: Conferences
calibration standard, flux, led, total luminous