Simulator for assessing the performance of polychromatic LED light sources

The unique properties of light emitting diodes (LED) offer significant advantages in terms of lifetime, source control, and response time all of which are potentially very important for various illumination applications. However, a number of factors such as the initial variability of the optical properties in a batch, high temperature dependence of the intensity and color especially of the red and amber LEDs and spectral degradation causing gradual intensity decrease and shift in color, need to be considered when developing LED light sources. The degradation and temperature dependence of the LEDs can significantly affect the performance of a light source over the operating period in terms of intensity and color stability, and efficacy. This is especially critical for polychromatic LED light sources, consisting of different types of LEDs with different spectral degradation rates and temperature dependencies. Therefore, a method estimating the intensity and color as a function of the affecting factors could be a valuable tool for developing LED light sources for various applications. In this paper, we present a simulator employing model-based estimation of the LED color, intensity, and efficacy as a function of temperature, forward current, and spectral degradation. The models are derived from the measurements of the electrical and spectral characteristic of the individual LEDs as a function of the forward current, junction temperature and corresponding thermal properties of the packaging. The results show that the simulator provides accurate estimates of the intensity and color of the LED light sources as a function of the temperature and forward current.