Charaterizing LEDs for Mixture of Colored LED light sources

Because of advantages such as long lifetime, low power consumption, and no mercury containing, LEDs are widely used in a variety of general-purpose illumination applications. There are two different approaches for generating white light with LEDs. The first one is the combination of phosphors excited by blue or UV LED emission, the other one is mixture of multi-color LEDs Without the power loss in the down conversion process of the white LED using phosphors, a higher efficiency and flexible option can be done with the mixture of multi-color LEDs. Questions arise on how the spectra of the mixture of colored LED designed are for good color rendering performance, more output lumens and better luminous efficiency. A lot of papers discuss the different spectrum combinations of multicolored LEDs which yield light with maximum efficacy, luminous flux and CRI, at the desired corrected color temperature, but most of them use the spectral power distribution of a model LED to calculate the luminous efficacy, luminous flux and CRI, and get the best combination as request. But as most people know, the spectral power distribution of a real LED will vary with ambient temperature, forward current and effect of aging, so simulation of the luminous efficacy, luminous flux and CRI will get some problems in practical. On the other hand, the finding of a better luminous efficacy of the mixture of colored LED can provide the best suggestion when the LED manufacturers try to select commercial LED chips to manufacture colored LED light sources. We setup a system with integrating sphere, spectrometer and four independent PC controlled powermeters, which can get the data of luminous flux, CRI and luminous efficiency of light sources automatically with different input power. Using the database from the system and simulations, we can analyze the optical and color characteristics of the mixture of colored LED light source, even the RGB LED (red, green and blue chips in one package). Then the se- lection of the combination of the LED chips for the mixture of colored LED light source, for generating more luminous flux, better color rendering index and luminous efficiency should be good.