Degradation of LED parameters during operation Brief review of currently used models and measuring methods

This paper brings a brief review of LED parameters that can be changed during the life of these types of light sources. Firstly the change of quantitative parameter of emitted light is presented (luminous flux) and following part is dedicated to change of quality parameter (spectral distribution) and change of electrical parameters. Modification of these parameters may affect the use of LEDs in lighting systems for general lighting and also in some applications with high demands on luminous flux and spectral distribution stability. Current attitudes to modelling and measuring methods and their fundamentals and deficiencies are reviewed briefly.