Most drivers assume that the time to replace a headlight bulb is when an existing one burns out. We recommend that drivers replace their bulbs every two years. Bulbs get dimmer by up to 20% over time and play a critical role in safety. The European Commission published a study that claims that driving with your lights on during the day reduces your risk of being in a fatal crash by 3% - 5%.
Many new cars have daytime running lights ("DRLs") that turn on automatically during the day. Depending on your specific type of car, your DRL might be a separate bulb or it might be the regular headlight bulb that runs at reduced wattage during the day. If you don't have DRLs on your car, simply turn your headlights on during the day and you will enjoy the safety benefits equally. Many drivers with automatic lights make a mistake when it comes to inclement weather. When your car's DRLs turn on, the taillights do not turn on - in rain, snow or fog, not having your taillights on raises your risk of getting rear ended significantly. Always turn on your headlights in inclement weather.
Using your lights more mean that they will grow dimmer faster and need to be replaced more often. This is a small price to pay for something that could literally save your life, but it does mean that you should replace your bulbs regularly. Bulb technology has been an exciting area of product development over the past few years. Many cars now have LED bulbs which consume less power and typically last longer. Incandescent (regular) lights have also enjoyed feature gains as well. You can now buy headlight bulbs with a blue or white hue and that are brighter than your stock bulbs.
If one bulb burns out, its counterpart bulb will likely fail in the immediate future. We recommend changing bulbs in pairs. If you only change the burnt out bulb, the new bulb will be significantly brighter. If the bulb housing has water or condensation in it - this does not mean that the housing is leaking. Bulb housing water issues typically are a result of the drain holes in the bottom of the housing being clogged - check these first.