by Jack Goho
Gideon Analytical Laboratories received several high-intensity discharge lamp (HID) assemblies for determination and cause of a white powder-like substance on the inside of the lens housing. The white powder diminishes the reflective properties of the light and overall effectiveness. HID lamps are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. The three-man types of HID lamps are mercury, sodium, and metal halide. These lamps are known for their high efficiency at turning electricity into light and their long rated life. HID lamps require a ballast in order to generate the initial surge of electricity needed to start them and to regulate their power during normal operation.
Failure analysis was conducted on the HID lamps. They were tested at low temperatures and purged with inert gases at various temperatures. Purging eliminated moisture, which was acting as a silicone sealant carrier in a confined high temperature. The white powder was coming from the silicone sealant material. The lamp assembly was taken apart and the white powder substance, along with parts of the glass lens, reflective casting, and sealant material all collected for SEM-EDS analysis.
SEM-EDS analysis of the white powder showed that it was rich in calcium and zinc. The powder was coming from the silicone sealant. There were a variety of chemical reactions taking place, evidencing that the sealant was not compatible with the reflector wall. This chemical incompatibility was amplified by confined space, extreme temperatures, and hygroscopic nature of silicone. A hygroscopic substance is one that readily attracts water from its surroundings, through either absorption or adsorption. Hygroscopic substances include cellulose fibers, sugar, caramel, honey, glycerol, ethanol, methanol, diesel fuel, sulfuric acid, methamphetamine, many fertilizer chemicals, many salts, and a wide variety of other substances.
Gideon Analytical Laboratories is a failure analysis laboratory with modern and state of the are research and analytical equipment. There is really no electrical problem we will not try to solve. From contamination to the capacitor, from transistor to transformer, and from component to PCB, we do it all. Voltage regulators, power supplies, MLCCs, LEDs, and HIDs are but a few areas in which we are experts. If it uses electrical current and it is not working properly, call Gideon Analytical Laboratories. Leave the problem solving to us.