Headlamps come in several sizes, shapes and types, as do their bulbs, which need periodic replacing. A majority of vehicles still use halogen headlamp bulbs, but a growing number come with high-intensity-discharge lighting that uses xenon gas instead of a filament, or with a cluster of LED bulbs that have a distinctive white light. The different types of bulbs are not usually interchangeable, but aftermarket conversion kits offer the opportunity to switch from halogen to xenon or even to LED, though that typically involves changing the wiring and adding components. Moreover, getting the full benefit of xenon or LED requires having headlamp assemblies designed for that type of bulb. Halogen bulbs are the cheapest, though more expensive replacements that claim to be brighter, more powerful and able to illuminate more of the road are available. Some of these claims are true, but federal regulations limit how far they can reach down the road. Bulbs legal for highway use can’t be so powerful they’ll blind oncoming drivers. In addition, halogen bulbs that claim to be brighter and whiter usually don’t last as long as the original-equipment bulbs that come on new vehicles. Sylvania, for example, says its SilverStar halogen bulbs have an average life of about one year. Original-equipment bulbs are typically the “long-life” type that should last for years. Xenon lights have a whiter color than halogens, with a slight bluish glow that gives them a distinctive appearance. Bulb manufacturers try to capitalize on this by offering halogen replacement bulbs that are tinted blue. Independent tests have shown, however, that these blue-tinted bulbs tend to produce less light, not more, than standard halogens, even though they’re more expensive. In addition to being brighter, xenon bulbs use less energy than halogens and last longer, but they’re more expensive to replace and also require ballast that may need periodic replacement. LEDs are the most expensive type of headlight and generate light through semiconductors. They last longer than other types – up to 10 years, by some estimates — and use less energy, which is one reason vehicle manufacturers are switching to them. Though LED headlamps last longer, replacing them because of an accident or other damage is likely to be more expensive than replacing other types would be. As with xenon lights, several companies offer kits to convert halogen systems to LEDs, though these kits often include only one LED bulb that fits into the original socket. LED systems typically use several bulbs arranged in a pattern to generate sufficient lighting, and experts warn that a single LED bulb doesn’t produce as much light as a single halogen and is not a good substitute.