Kelvins, commonly abbreviated as K, are units of measurement that measure the colour temperature of a light. Although the term may be confusing, colour temperature has little to do with the actual temperature of a bulb. Instead, it refers to the colour of the light produced by the bulb.
You may notice that some bulbs produce a very warm yellow or orange light. These bulbs fall on the lower end of the Kelvin scale. The natural light from a candle, for example, would fall somewhere under 2000 Kelvin, or 2000K. Standard halogen headlight bulbs typically have a colour temperature around 3200K to 4600K. Bulbs in this range will have a nice white light, but won’t be extremely bright.
As we move up the Kelvin scale, lights get whiter. This can make the light appear much brighter, although Kelvins don’t measure actual light output. Many drivers prefer bulbs with a higher Kelvin rating because they seem brighter and make it easier to see at night. Maximum performance headlight bulbs start at around 3900K. Some have an even higher Kelvin rating, meaning the light they produce appears whiter.
At the higher end of the Kelvin scale, you’ll find bulbs that have a blue tone. Xenon HID bulbs, which have become popular in recent years, typically have a high Kelvin rating. These bulbs appear extremely bright thanks to their cooler colour temperature.
Styling bulbs with a very cool colour temperature are also popular, although they are not always street legal. Halogen styling bulbs have colour temperatures up to 5000K. Xenon HID styling bulbs are even further up the Kelvin scale, with some reaching up to 7000K. However, most of these very high Kelvin bulbs are too blue in colour to be road legal, so they can only be used for styling purposes.
What Are Lumens?
A Lumen is a unit of measurement that measures how bright a bulb is. Unlike Kelvins, which only tell you how yellow or blue a bulb appears to be, Lumens give the actual light output of a bulb. This is useful when searching for a brighter bulb. While a bulb with a high Kelvin rating may appear brighter, a bulb with more Lumens really is brighter.
Halogen headlight bulbs usually have around 3000 Lumens. This is plenty of light for most drivers and will be sufficient for you to see at night. Even maximum performance halogen headlight bulbs fall somewhere around 3000 Lumens, though a higher Kelvin rating may make them appear brighter.
To get a truly brighter bulb, you would need to switch to Xenon HID headlight bulbs. These typically measure in at around 5000 Lumens—significantly more than halogen bulbs. They not only appear whiter and brighter than the average halogen bulb, they deliver better performance.
What About Watts?You may be wondering what happened to measuring bulbs in Watts. Before new innovations, such as HID bulbs and LED bulbs, most light bulbs were measured in Watts. This is true not only for car bulbs, but also for bulbs in your home.
Watts measure how much energy a bulb uses. When all bulbs were incandescent or halogen bulbs, this was a useful way to describe the brightness of a bulb. However, new bulbs are much more energy efficient. Therefore, a bulb may use fewer Watts but produce more Lumens. A cooler colour temperature, measured in Kelvins, can also make a bulb appear brighter.
Knowing the number of Lumens produced and the Kelvin rating of a bulb will give you a much better idea of how bright a bulb is compared to measuring the Watts.
How Do I Choose the Best Bulb?When searching for the best headlight bulb, take note of both Lumens and Kelvins. A bulb with 3000 Lumens or more will be bright enough for just about every driver. If you want an even brighter bulb, HID headlights are the way to go.
When it comes to Kelvins, it’s a bit trickier to choose the right bulb. Anything between roughly 3000K and 5000K should do the job. Within this range, bulbs closer to 5000K will appear whiter and brighter. More than 6000K, and your bulbs will have a bright white-blue glow and may not be street legal.