Besides its richness in colors and having a good color rendering, the LED lighting has another advantage that it can be easily controlled dynamically. Generally speaking, it is difficult for traditional luminaries to adjust their colors and color temperatures. Thus in order to achieve dynamic illumination in different situations, lots of luminaries should be used. But as for the LED lighting, especially for the tricolor white light LED, it is easy to change between different colors and also between different color temperatures by only adjusting the input current. The LED lighting has the following light mixing methods: (1) analog; (2) pulse width modulation (PWM); and (3) frequency modulation. For example, in a Boeing 787 airliner, a technique that simulates sky light is used in the LED illumination luminaries in the passenger compartment. The LED light source can simulate the dawn-dust change in a day by changing its color temperature and brightness in order to improve the sleep quality of passengers on a long trip.
As for the most prospective tricolor white light LED lighting, how to keep stability of color has become another important issue. The light extraction properties are also different. After being in used for a period of time, the rate of the main wavelength, half-width of spectrum, and peak power of the LED with different wavelength will change. The change will cause the color temperature to drift in mixed light. It is reported that the extent of this color temperature drift can reach over 1000K, which affects the use severely.
