A study to obtain a fluorescent dye suitable for use in detecting the presence of thin-film electrical contact lubricants has been conducted, and it has been found that BBOT [2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene], a scintillation-grade blue fluorescent dye, is a much improved replacement for the presently used proprietary green fluorescent organic dye. Using quantitative fluorometry, it was determined that the fluorescence intensity from a lubricant film deposited from a solution containing 0.01 percent BBOT is about six times greater than that from a film deposited from a solution containing 0.02 percent of the organic phosphor. The fluorescence intensity of the BBOT changes very little with time and exposure. With the organic phosphor, after seven days the intensity decreases by about 90 percent, below that which can be visually detected using ordinary long wave UV-light. BBOT, in amounts twenty times (0.20 percent) the concentration required, appears to have no detrimental effect on contact resistance, giving a maximum shift in contact resistance distribution of about 200 micro ohms. BBOT is nontoxic and safe for use. On the basis of this, contact lubricant specifications are being revised to replace the organic phosphor with BBOT. These studies suggest that fluorescence techniques can also be used to measure and monitor contact lubricant film thickness and distribution.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983