X-ray absorption of the Hg distribution in a commercial metal-halide lamp

The radial temperature profiles of a commercial metal-halide lamp and of lamps containing its individual components have been acquired using x-ray absorption of Hg density distribution. The temperature profiles were determined by combining the measured absorption of the spatially resolved Hg density with the wall temperature. The lamps studied were a commercial lamp, i.e. the Philips CDM-T 70 W/830, and identically shaped lamps containing NaI, DyI3 and TlI separately. It was found that the element Dy contracts the arc, Na broadens the arc while Tl causes the arc to have so-called 'shoulders'. Combined in the commercial lamp this leads to a wall-stabilized arc without contraction and 'shoulders'. A reproducibility test with identical lamps was also made and showed that the uncertainty in the temperature profile is about 8% for the absolute temperature and only 1.6% for the actual shape of the profile.