Thermal management of remote phosphor layer in a light-emitting diode system

Abstract

The heat generated in the phosphor locations, due to phosphor quantum inefficiency and Stokes shift losses, accumulates around the local volume due to the low thermal conductivity of the phosphor binding material. This issue is compounded as the localized heat builds up within the phosphor binding material, causing phosphor quenching and degrading the binding material, resulting in more absorption of visible radiation and in turn building up more heat. The increase in temperature contributes to faster degradation of light in the short and long term.

A discussion at the end includes how to overcome the light trapping issue and improve the method used to lower the phosphor layer temperature without reducing the luminous flux.

In response to the need for thermal management of the phosphor layer, an experimental study was conducted to evaluate and quantify the effectiveness of a method to dissipate the heat generated in the phosphor layer to the ambient. The experimental findings verified the feasibility of the method, but it reduced the luminous flux from the package due to surface absorption of photons by the structure used for dissipating the heat.

From the indicator-type light-emitting diode (LED) to the high-power illuminator-type LED, the evolution of solid-state lighting rests heavily on the extraction of generated heat from the LED chip. With the increase in lumen packages of high-power LEDs, the LED chip as well as the down-conversion phosphors require dedicated paths to dissipate the excess heat created in a smaller volume inside the LED package. If not properly dissipated, both short-term and long-term performance of the LED will be compromised. The goal of this study was to evaluate the feasibility of a thermal management technique to reduce the phosphor operating temperature without adversely affecting optical efficiency.