LED-based standard source for spectral radiance with high uniform luminance plane

Abstract

A standard source for spectral radiance is necessary for instruments, such as spectral radiance meters, which measure luminance and color of displays. Nevertheless, unavailability of practical transfer standard sources for spectral radiance has long presented difficulties for manufacturers. To overcome the difficulty of spectral radiance traceability chain, the National Metrology Institute of Japan has developed an LED-based standard source for spectral radiance by combining a broadband LED module and a luminance homogenizer. The developed standard LED achieved average luminance of approximately 10 000 cd/m2 at 160 mA operating current. The spectrum is spread over the entire visible range using the broadband LED module as a source. With the new luminance homogenizer, the luminance variation on the aperture plane was achieved as 0.1 % within 10 mm diameter (root mean square). The plane uniformity and the uniform area size are striking, improving the plane uniformity of traditional ribbon filament lamps and beyond that of a portable integrating sphere source. Using the standard LED, manufacturers are expected to obtain new convenient traceability schemes while profiting from their high practicality.