Improvement of ceramic-halide high intensity discharge lamps: Study of the UV radiation that could be converted into visisible light

In the field of lighting and for devices such as big panels, leds remain less interesting compared with the high-pressure lamps which are preferred for their high illumination coupled to a correct IRC index and lifetime. For these lamps, the challenges consist in illuminating most efficiently in the visible spectral region and in reducing mercury inside the lamps. Among the solutions, we can put in additives having a high power radiation (calcium, sodium, dysprosium, thallium, and strontium), and\or find free mercury gases (mercury being usually mixed with pure argon). For such mixtures at high pressure, the radiative spectrum goes from UV to IR radiations. The UV radiations can be very important and could be absorbed and converted by phosphors in order to increase the visible light and reduce the skin diseases. Unfortunately, adding phosphors leads to expensive post-treatments. A theoretical study of the radiative spectrum seems more adapted and cheaper to estimate the radiation emitted in the IR, visible and UV regions. This radiative energy is often deduced according to simplified approaches1. Here, we propose a more accurate method, usually applied to evaluate the divergence of the radiative flux in thermal plasma modeling: the Net Emission Coefficient2. This method allows a good and rapid estimation of the total power emitted by the center of the lamp, by keeping a good description of the radiative mechanisms in the different spectral intervals (IR, visible and UV). The lamps we are studying work with a primary gas between 10–500 mbar, 5–40 mg/cm3 mercury, and metallic additives between 1 and 30 mg/cm3. The partial pressures are 200 mbar for Ar, 10 bar for Hg and 1 bar for metallic species with maximal temperatures around 5500K in the center of the lamp and plasma size of 1mm. We present the radiation emitted in the three spectral regions for different mixtures: 89%Hg-2%Ar-9% additives, the binary mixture 98%Hg-2%Ar often used in lamps, and a ficticious binary free mercury mixture at 11.2bar. The results show the radiation proportion emitted in each spectral interval (IR, visible and UV), and allow us to evaluate the UV part that can be converted in visible light. We also show the increase of the radiative power due to the presence of the metallic species and particularly in the visible and UV regions. The free mercury mixture is studied in order to evaluate the capacity of free mercury lamps to be good candidates.