Modeling the role of phosphor grain packing in compact fluorescent lamps

Compact fluorescent lamps contain mercury gas which generates ultraviolet radiation. A thin powder layer constituted of rare-earth oxides is coated inside the glass tube. The role of this layer is to convert the inside ultraviolet radiation into outside visible radiation. We focus here on a particular powder layer, constituted by phosphor grains. The phosphor layer has to achieve two distinct goals. On the one hand the grains have to absorb the maximum amount of ultraviolet radiation in order to generate visible light, and on the other hand the transmission of visible light has to be maximized in order to optimize the efficiency of the compact fluorescent lamp. Here, we study the influences of grain size, grain shape, density of packing powder, and thickness of the phosphor coating. Such a study is a first step towards a better understanding of the conversion efficiency of ultraviolet radiation into visible radiations, and can eventually, help to improve the production line of compact fluorescent lamps. All the presented simulations were performed with the commercial software LightTools® using a ray tracing method.