Analysis of factors affecting color distribution of white LEDs

The color uniformity is a critical index in the evaluation of high quality white light emitting diodes (LEDs). The main factor affecting the color distribution is the state of the phosphor. The secondary factor is the optical structure. This paper analyzes two parameters of the phosphor layer (thickness and concentration) and six optical structures. Results indicate that the structures with reflector have lower color uniformity. The hemispherical shape of phosphor layer could improve the performance of color distribution and make the variation smaller. Between the two parameters of phosphor, the concentration has the greatest impact on the color uniformity, the second one is the thickness. Through the analysis, it is suggested that the thickness and concentration should be precisely controlled. Otherwise, the color uniformity will be varied significant and may generate serious yellow rings.