Headlight Brightness

Headlight brightness is critical to safe driving. Too dim, and the road ahead will not be adequately illuminated. Too bright, and the life of the headlight will be shortened, making it prone to early burnout. In most cases, the headlights are more likely to be too dim than too bright. Bulbs that are too bright indicate that either the charging system voltage is too high and needs to be measured with a DVOM or someone may have replaced the headlights with an aftermarket set, which may be illegal. Checking bulb numbers will verify this condition.

If the headlights are too dim, there can be several causes. The most common one is high resistance in the light circuit. This can be checked by measuring the voltage drop on both the power side of the bulb and the ground side. The voltage drop should be less than 0.5 volts on each side. If an excessive voltage drop is indicated, use a wiring diagram to research the circuit. Once you know how it is wired, use the DVOM to isolate the voltage drop by using the meter to measure each segment of the circuit. When the high resistance is located, perform the needed repair, whether that is a wire repair or a connector, switch, or relay replacement. If the voltage drop is less than 0.5 volts on each side, suspect the light bulb is wearing out. One way to verify this is with a light intensity meter. This meter can measure the amount of light energy the lamp is producing, so you can compare that to specifications. If the light is being supplied with the specified voltage, but it is not creating enough light, the bulb will need to be replaced.