A new traceability chain for luminance scale with LED-based transfer standard

Abstract

A new traceability chain for luminance scale is proposed for light-emitting diode (LED) luminance measurement, which utilizes a newly developed LED-based luminance standard source (luminance standard LED) as a transfer standard. Compared with conventional traceability chains for LED luminance measurement that rely on either a luminance meter to transfer the scale from the primary to the user level, the proposed scheme has a two-fold advantage. Firstly, color correction is made at the traceability source and the user is freed from performing this complicated task. Secondly, the luminance standard LED acts as the reference source for comparison measurement with a luminance meter and no other extended source facilities such as integrating spheres are necessary at the user site. Performance evaluation of the luminance standard LEDs showed spatial uniformity better than ±2.0% within a 7 mm diameter area and temporal stability of 0.01% during an 8 h operation, which verified the LEDs’ capability to serve as a reference standard source. Calibration of the luminance standard LED was performed on the luminance scale realized by illuminance to luminance conversion, and the calibration uncertainty was estimated to be U = 1.4% to 1.7% (k = 2) at the traceability source. It is expected that this will enable users to obtain luminance measurement uncertainties comparable to the conventional traceability schemes while profiting from the high practicability that the proposed scheme provides. The luminous standard LEDs are now used in a new traceability chain in Japan, contributing to improved reliability of the luminance measurement of a wide range of LED-based products such as displays.