NCJ Number
132203
Journal
Canadian Society of Forensic Science Journal Volume: 24 Issue: 2 Dated: (June 1991) Pages: 91-96
Date Published
1991
Length
6 pages
Annotation
The actual temperature of the off filament adjacent to the incandescent filament in a double beam headlight was measured at specific times under conditions duplicating those of a sealed headlight.
Abstract
Experiments were performed in an apparatus consisting of a bell jar on an aluminum base fitted with a nitrogen source, argon/nitrogen source, a vacuum pump, a pressure gauge, a thermocouple meter, and the inside and outside electrical leads connected to a headlight and power supply, respectively. The thermocouple probe was placed on the front surface of the filament that was to remain off in the two filament headlight. A lens covered the filaments while allowing the gases, 88 percent argon and 12 percent nitrogen at a negative pressure of 600 millimeters mercury, to circulate. The maximum temperature of the off filament was reached in 60 seconds after illumination of the adjacent filament. For the low beam filament, the maximum temperature ranged from 686 to 870 degrees Centigrade (C); for the high beam filament the range was between 688 to 929 degrees C. Since sealed beam glass has a softening point of 750 C, the temperature of a filament would have to be in the range of 800 C for sufficient heat to transfer to the glass particles to cause them to melt on the filament. The high temperatures recorded in these experiments indicates that the temperature of the off filament at the time a headlight is broken is sometimes high enough to melt small particles of glass on its surface. 1 table, 3 figures, 4 notes, and 5 references (Author abstract modified)