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Which Bulb Should I Choose?

If there were one best bulb, there would only be one.
Your choice of bulbs is based on a number of factors including where you go, why are you going there and what will you do while your are there? First, some basic information about bulbs and light.
What is Bulb Output
There are two aspects to light output. The quantity of light, which is measured in Lumens and is roughly proportional to wattage, and the color of the light which is measured in temperature, degrees Kelvin (ºK)
Incandescent Bulbs
Any bulb that uses a filament, normally tungston, to generate light is an Incandescent bulb. When the lamp is on, Tungson atoms are cast off of the filament. As long as they don't touch anything, most of them will return to the filament when the bulb is switched off. When enough atoms fail to return to the filament the filament will fail and the bulb is "burned out". To extend the life of the bulb, the globe is made larger as the wattage of the bulb increases. This gives the atoms more room to fly around without contacting something. The dark shadow on the inside of a bulb that has been in use for some time is caused by the collection of Tungston atoms. Incandescent bulbs were used in automotive headlamps for decades, but they had a few problems. To increase the output of headlamp bulbs would require much larger globes. The incandescent sealed beams and bulbs used in the 1940's, 50's and 60's were rated at 40 watts or less and produced a very yellow light. A 60 watt incandescent bulb has a 2.5" diameter globe and only makes about 850 lumens. A modern automobile need twice that many lumens to be operated safely.
Halogen Bulbs
Halogen bulbs were developed to address the problems of the standard incandescent bulb. They differ from plain Incandescent bulbs in that the gas in the globe is under pressure. The globe is thicker to contain the pressure. Having the gas under pressure allows the filament to burn hotter to produce more light and a whiter light while still having a reasonable life. The pressure causes the Tungsten atoms, which are thrown off of the filament to return to the filament and to do it in a much smaller package. At the same time the output of a 60 watt Halogen bulb has increasted to about 1500 lumens and the color of the light has increased form 2800°K to 3200°K. The size of a halogen bulb has been reduced to less than 3/4" diameter which allows some headlamp assemblies to be about 2.5" in diameter. For more discussion on how Halogen Bulbs work, click this link.
Increasing Bulb Output
There are two common ways to increase bulb output.
 1) Increase the wattage. This is done by increasing the mass of the filament so that its impedance, or resistance increases and in turn causes an increase in power required to reach incandescence. The relationship between wattage and Lumen output is not linear. Higher wattage bulbs put an increased load on the electrical system of the vehicle. In addition, a high wattage bulb can create enough heat to damage a lamp if it is not capable of handling the heat. Putting a high wattage bulb into a very small lamp can also result in short bulb life. We have had customers put high wattage bulbs into a Micro DE Fog lamp, one our finest lamps, made of cast aluminum and glass, and have the bulb last only a week or so. Only standard wattage bulbs are legal for highway use. Upgraded bulbs are sold for off-road, or racing purposes only.
 2) "Overdrive" the filament and create what is commonly known as a Xenon Bulb. This is done by reducing the diameter of the filament and extending its length to maintain its original mass. This obviously results in more light, but a more fragile filament  The addition of Xenon gas to the gas mix in the globe acts as a cooling agent to extend the life of the bulb. The amount of Xenon Gas used and the design of the filament are two of the factors that engineers can vary to produce a product that has the characteristics the Sales Department feels will meet the needs of the market they are addressing. There are no further returns to a Xenon gas mix exceeding 7% and that is commonly refered to as a 100% Xenon blub. Some manufacturers use the term +80% or +100% to indicate an increase in light output. We know that the Philips Extreme Power (XP) claims an 80% increase in lumens and the Hella Premium 50% has a 15% lumen increase. There is no industry standard. Manufacturers can claim whatever they want and let the buyer beware.
 3) The best of both worlds is available with the Osram Hyper bulbs. They have both an overdrive filament and a slightlly higher wattage. We have received reports that these are the best performing bulbs available that don't require a wiring upgrade. Hyper bulbs are only available in H4 and H7 versions and are sold for off-road, or racing purposes only.
Bulb Life
The product of a light bulb is light and heat. Since bulbs are not 100% efficient, the amount of heat also increases with a higher wattage bulb. A high wattage bulb has a life less than half that of a standard wattage bulb. Many are manufactured with a target life of only 50 hours!! The additional heat from the higher power consumption weakens the filament substantially - then the normal vibration in an automotive environment takes it out! Rallyists use bulbs with wattages as high as 160, but they replace them before every event.

Higher Wattage and your Wiring
Typically, with noted exceptions (VW and Audi), if you keep output of your bulbs at 100W or lower, you will have little problem with meltdown of the OE wiring or controls as long as the wiring is in good shape and all connectors in the circuits are clean and free from corrosion. Bulbs over 100W can cause melting of the connector, overheating of the wires and failure of the headlamp switch and dimmer switch. You do not want to replace the dimmer switch on most cars as it is very labor intensive and will cost hundreds of dollars for parts and labor.

Do I Need to Upgrade My Wiring?
Before you spend the money for upgraded bulbs, you might want to evaluate your wiring. First, with a good Voltmeter, measure the voltage output of your alternator. With the engine off, clip the leads of the Voltmeter to the alternator and tie them back so they don't get tangled in the belts or the fan. Start the engine and run it up to about 2000 rpm. Note the voltage and shut off the engine. Now move the Positive Voltmeter lead to the back of the bulb - you'll have to pierce the insulation to do this. Leave the ground lead where it was. Now start the engine again and turn on your lights. Note the voltage, shut off the engine, remove the test leads and reseal the punctured insulation with Silicon RTV. If your drop is over 1 volt, you have some repairs to make even before you upgrade your bulbs. Look for loose or corroded connections, loose or corroded fuses or relays. Repair any problems.

Light Color
The color of light is measured in Degrees Kelvin (ºK). We have all heard the terms "Red Hot" and "White Hot", well, white hot is in fact hotter (4000-6000°K) than red hot (1500ºK). Daylight is about 4500°K. A normal halogen bulb emits a light with a straw color and a color temperature of about 3200° K. An amber fog lamp is normally in the 2600°K range and an HID (Xenon) lamp is in the vacinity of 4300° K.

Why do we care what color our headlamps and other lamps are? Objects do not emit a particular color of light, but they do reflect certain colors of light. If only one color of light is shown on an object then only that color will be reflected. Shine a blue flood light on an object and it will appear in shades of blue. White is not a color, but a mixture of all colors. For this reason. we want our headlamps to be as white as possible and so that we see colors and contrasts best. 

A very white light, 6000ºK or higher, is into the ultraviolet end of the spectrum. Blue is not the easiest color for the human eye to see, green Is. A blue white or "Cool White" light can cause eye strain. The illegal 20,000°K HID kits, that look like a blue neon sign, are a good example of how hard it is to focus on blue. In bad weather where white light is reflected back into the eyes of the driver, eye strain is a major problem. If you have ever driven in a "White Out" snow storm, you know how tired your eyes are when you get where you are going.

A yellow light has much more green in it and as such is much easier to see. Fog lamps used to have amber lenses to reduce eye strain, but the Cadmium was outlawed because it is a heavy metal and the green movement was concerned about it in land fills. Turn signals are amber in all ECE countries because the color makes them stand out in a sea of red lamps. For many years, the French required yellow headlamps because they stood out among all the other white lights. The French have dropped that requirement.

We can effect the color of the light produced by a bulb. An overdriven halogen bulb has a color as high as 3600°K, but you can't go much higher because Tungsten melts at 3695°K. To make the light any whiter, we have to add a filter. A blue filter will reduce the remaining yellow to make a whiter light with a color as high as 4000°K however any filter will reduce the amount of light passing through. The result of a Xenon bulb with a blue filter is known in the industry as a Xenon Blue. This is the the most popular type of aftermarket upgrade bulb and includes the Sylvania Silver Star, Osram Night Breaker, PIAA XTreme White and our own Hella High Performance Xenon Blue. There are some manufacturers out there who claim color temperatures from halogen bulbs as high as 5000° K. Figures don't lie, but liars can figure.

Relay Circuits
After you get your wiring up to snuff, measure the voltage at the bulb again - then decide if you want to upgrade your wiring with relays and power directly from the battery. If you are dropping over 1 volt, your wiring or a connection somewhere is starting to act like the heating element in a toaster oven then you need to upgrade your wiring. For more information on relays and how to wire them, click here.