Which headlight bulb should you choose?

"Bright eyes burning like fire...."

  The headlight bulb went the other day. In most cars I can ignore this until servicing time or the next MOT. I know a lot of other Torquecars members will have a go at me for this but I am often too busy to get involved with changing bulbs and I still have a driving lamp on that side anyway.  However in my Audi it is not possible to ignore this, each time you turn the lights on the car will beep a warning message at you and patronise you for your entire journey by showing you a picture of an amber bulb with an X through it.

Normally I wouldn't mind but I had changed the bulb recently for a spare, which I obtained from a headlamp assembly I purchased from a scrap yard. Sadly though this only lasted a couple of weeks so I had to go to a shop and actually buy a bulb.

There was an amazing selection to choose from. When confronted with choice we humans usually make silly decisions and go with the cheapest or most expensive option or just altogether give up and leave the shop.

I resisted the urge to do the latter and went over the options open to me. There were bulbs that were 40% brighter than normal ones at twice the cost. Then there were bulbs which had a bluish hue and claimed to run at the same temperature as HID lamps at a similar price to the 40% brighter ones. (Having tried these before I was disappointed that the light emitted did not have a the bluish hue the packaging had subtly implied but not actually stated!) Then there were bulbs that were 80% brighter than standard.

I would guess that with a fixed wattage going in the brighter bulb would be more efficient and emit less heat and more light. I was also hoping for the brightest light I could get. Then the top shelf caught my eye. It had super high wattage bulbs on it. Peaking at 80W of pure light they seemed to offer everything I wanted. Sadly though after reading the packaging I determined that these were only legal for street use on cars registered 100's of years ago.

History of headlight bulbs.

Almost as soon as the motorcar was invented the headlight appeared. Early ones were in a fixed headlight unit so the whole thing had to be changed. They used Tungsten filaments and this was actually fairly inefficient. Heat output was high so light output was much lower. The light given off appears to be yellow because it is at the lower end of the light spectrum. The filament also burns out slowly over time so as it gets older it gives off less light.

Then we had a breakthrough in Tungsten Halogen technology. Now over 30 years old this technology has been refined and perfected to give us the range of bulbs we have today. Early bulbs were made of heat resistant Quartz and then later bulbs were made from heat resistant glass. The gas used is generally Argon although called halogen in this application! These bulbs can burn longer and hotter so are able to give off more light giving it a whiter appearance. The brighter you go the whiter the light gets. Modern lights now use Xenon/halogen gas mix which enables the filament to last longer.

HID is the new kid on the block and sadly most upgrade kits are not legal. These take a few minutes to reach full light intensity although they obtain 70% brightness within a few seconds. In the UK cars need automatically levelling headlights to make these legal. These lights give a bluish/purply hue do to the light frequency they emit. HID was not an option open to me so I will discuss HID headlights in another article in more detail.

So what did I go for and was it worth the money?

It is annoying keep changing the bulbs for MOTs and having other drivers flash you so I opted for the 80% brighter ones and set about proving to myself that they were worth the 3 times the cost of a standard bulb. I replaced the bulb, but this time round it only took a few seconds. This was probably due to the fact that I had loosened up the housing and connectors last time plus the knowledge I gained on which orientation the bulb required to clear the battery and other components.

I then did a very thorough scientific test. Leaving the standard bulb in the other light and cleaning both lenses to establish a matched control group I turned on the engine and switched on the lights. Then I got out of the car, walked a hundred paces and turned round to inspect the bulbs. I really shouldn't be so cynical. The new bulb was clearly brighter than the other one. As I moved from left to right and then moving in closer I continued to check for brightness and my original conclusion was right. The new bulb really was brighter. It is hard to judge 80% brighter by eye so perhaps I will get my cameras light meter out and take some measurements.

It is worth noting that often brighter bulbs and higher wattage bulbs have a much shorter lifespan. I will be keeping and eye on the life of the new bulbs carefully and will report back my findings.