" Photometric quantities " are important characteristics for lighting, and "total luminous flux" is used as a performance index of light sources. The total luminous flux value of a light source is measured by comparison with a standard light source that has a known total luminous flux value.

Calibration for widely used omnidirectional light sources has mainly used a standard lamp in the form of an incandescent lamp. This standard lamp has a filament, a glass bulb, and other parts with shapes suitable for a omnidirectional light source, and is handcrafted one by one by highly skilled and experienced artisans using specially selected materials to achieve high stability and reproducibility of optical power intensity. High-quality standard lamps have supported the progress of the lighting industry to date in areas such as quality control at manufacturers and characteristics evaluation of newly developed light sources.

However, with the recent spread of LED lighting, the impact of reduced and discontinued production of incandescent lamp is also extending to the standard lamp, and there is strong demand for a new standard light source that will support the future lighting industry in place of the standard lamps. For this reason, R&D of a new LED-based standard light source to take the place of the standard lamp is being actively pursued mainly by the national metrology institutes in various countries. The light source that will replace the standard lamp used thus far must have high stability and reproducibility of optical power, a spectrum covering the full visible wavelength range, and spatial light distribution that emits light in all directions. However, it is not easy to satisfy all of these characteristics at a high level, and a light source that can sufficiently replace the role of the existing standard lamps have yet to be developed.

Researchers in AIST developed a prototype of a new omnidirectional standard LED in collaboration with Nichia Corporation. This is a new standard light source using LEDs that emits light covering the full visible wavelength range over all directions.

The developed omnidirectional standard LED achieves stability and reproducibility of optical power comparable to the conventional standard lamp and has a spectrum covering the full visible wavelength range. Furthermore, combination with a special optical material that diffuses light uniformly in all directions successfully realized spatial light distribution that is ideal as a standard light source for total luminous flux measurement. The commercialization of the standard LED is expected to contribute to the sustainable development of lighting industry and to improve the accuracy of light source evaluation in manufacturers, etc.