ABSTRACT
INTRODUCTION Light emitting diodes (LEDs) are rapidly coming to general lighting. Small size, long lifetime, high efficacy and cold light are the advantages that are commonly mentioned. LEDs offer also some other advantages compared to traditional light sources. White light can be made from LEDs either using blue or UV LED and phosphors or alternatively mixing different coloured LEDs. Using the latter implementation, it is possible to attain better efficacy and the use of different colours gives also some additional benefits. When white light is created mixing several different coloured LEDs, it is possible to change the colour and colour temperature. The possibility to change colour temperature will give designers several new possibilities. Artificial light can be matched to daylight variations, atmosphere of restaurant and other places can be easily changed. Earlier, systems capable of such variations have been complex and expensive.
