Smart White LEDs with Tunable Correlated Color Temperatures through Single-Chip Packaging

In this paper, a new method to regulate correlated color temperatures of white LEDs is proposed for the single -chip packaging structure. Its principle is based on modulating the blue light radiation distribution on patterned red/yellow phosphor layer through changing the paraffin layer transparence. The presented method has been demonstrated by experiments. The influences of the paraffin layer thickness and the phosphor layer concentration on the correlated color temperatures were tested and analyzed. When the thickness of paraffin layer is 1.2mm and the concentration of yellow and red phosphors is 30wt%, with the increase of voltage, the correlated color temperatures of white LEDs increases from 7886K to 9793K, then decreases to 3378K. Its modulating range of correlated color temperatures reaches 6415K. The paraffin layer has little bad effect on the luminous efficiency. The reduction of luminous efficiency of white LEDs is less than 10%.