Effects of voltage drop on the rise time and light output of incandescent brake lamps on trucks

This study evaluated the effects of voltage on rise time and light output from incandescent brake lamps for a range of voltages representing realistic values for large trucks. The findings indicate that, relative to nominal voltage of 12.8 V, realistic voltages for large trucks lead to significant increases in rise time and to decreases in light output. At 9 V, for example, 90% of the asymptotic light output is reached about 113 ms later than at 12.8 V, and the asymptotic light output is about 28% of the output at 12.8 V. Analogous comparisons of 6 V with 12.8 V indicate an increase in the rise time to 90% of asymptotic light output of about 316 ms and a decrease in asymptotic light output to about 5%. The changes obtained in rise time and light output of incandescent lamps as a function of voltage are of practical importance because they can be expected to increase following drivers' reaction times to brake signals and to increase the frequency of missed signals.