Light-emitting diodes are compound semiconductor devices that convert electricity to light. In optical radiometry and calibration

LED has good performance of high luminance

energy-cost savings

long life

no pollution and small bulk. It is new reference source of radiometry

photometry and colorimetry. In this text

design of spectrally tunable LED light source has been described. It composed of an integrating sphere with a large number of LEDs. The source is designed to have a capability of producing different spectral distribution in the visible region

and it can mimic various light source. A series of simulations have been conducted to predict the performance of spectral distribution of the designed tunable source. The source has designed a power control box

it can control every LED module accurately. This new type source will be used as a transfer standard for radiometric application.