Light-emitting diode (LED) standard lamps are interesting since the traditional incandescent standard lamps for photometry are difficult to obtain. Many of the National Metrology Institutes have started projects to study the use of LED standards for photometric comparison. The National Institute of Metrology, China, has developed a type of LED filament lamp for total luminous flux. The lamp mimics the 4π incandescent standard lamp and has no space for an active temperature control component. A temperature dependence correction method is reported using the coefficient of the lamp voltage to the output luminous flux. The luminous flux correction is derived from the lamp voltage value. By applying correction, the stability test of the LED filament lamp shows that the ageing effect was estimated to be less than 0.1%/210 days. The temperature dependence was suppressed to less than 0.1% for a range of 21 • C ± 2 • C, which could be due to possible temperature fluctuations of the lamp ambient temperature during measurement by the goniophotometer or integrating sphere.

Light-emitting diode (LED) is now the main type of light source in global lighting marketing. However, traditional photometry with incandescent standard lamp is not sufficient to implement high level LED photometric measurement since a considerable spectral mismatch error may exist if the photometer has a large general V(λ) mismatch index . LED standard lamp is proposed to be the complementary transfer standard for photometry to reduce this measurement uncertainty. National Institute of Metrology, China (NIM) has previously reported a type of LED filament lamp for total luminous flux. In this article, NIM demonstrates another type of LED filament lamp for luminous intensity calibration. The LED filaments are sealed in T90 cylinder glass bulb as emitters, and has a spectrum similar to the reference white LED spectrum considered in Commission on Illumination (CIE) technical committee 2-90. The LED lamp uses the E27 screw base as the connector, and is compatible with the traditional alignment approaches. The warm-up time is less than 12 minutes. The output change of a group of 12 lamps, over a nearly two years of storage and 1 hour operation every day during the whole long term test, is found to be ±0.2 % or less for most of the lamps. The ageing effect of one lamp over a continuously 6500 hours burning is estimated to be -0.014% per hundred hours, and it is significantly lower than 1% per hundred hours, the typical drift rate of traditional incandescent luminous intensity lamp. In the aspect of the coincidence with inverse square law, the LED lamp has a similar performance to the WI41/G lamp, the traditional luminous intensity lamp.