Types of Lamps

Modern vehicles use many different kinds and sizes of lamps, also known in some places as light bulbs or light globes. There are several lamp types available, including standard incandescent lamps, halogen lamps, vacuum tube fluorescent (VTF) lighting, HID xenon gas systems, LEDs, and more. Conventional incandescent lamps are being replaced in many applications by these other more efficient types of lights.

Incandescent and Halogen

Incandescent lamps consist of one or more filaments that heat up to approximately 5000°F (2760°C) and glow white hot Figure 39-3. The filament material does not burn because most of the oxygen in the bulb has been replaced by inert gases that stop combustion from occurring. The power in watts consumed is often marked on the lamp; wattage (work performed) is found by multiplying the voltage used by the lamp by the current flowing through it. The higher the wattage, the more light that can be created when compared to a similar type of bulb. Incandescent bulbs are inefficient, converting only about 10% of the electricity to visible light.

FIGURE 39-3
Incandescent bulb with single filament.
FIGURE 39-4
Halogen bulb.

Halogen lamps are another type of incandescent lamp, but they are filled with a halogen gas such as bromine or iodine Figure 39-4. These lamps have a much longer life and are generally brighter and produce more light per unit of power consumed. However, they become very hot in use. They are manufactured from highly heat-resistant materials, and the bulbs must be handled carefully because they are sensitive and can be damaged even by finger oil residue left by fingerprints.

Vacuum Tube Fluorescent

Vacuum tube fluorescent (VTF), also called vacuum fluorescent display (VFD), is used for instrumentation displays on vehicle instrument panel clusters. This type of lighting emits a very bright light with high contrast and can display in various colors. Usually VTF displays are of bar graphs, seven-segment numerals, multisegment alphanumeric characters, or a dot-matrix pattern. VTF displays include different kinds of alphanumeric characters and symbols to alert drivers of various conditions.

High-Intensity Discharge

High-intensity discharge (HID) headlamps produce light with an electric arc rather than a glowing filament Figure 39-5. The high intensity of the arc comes from metallic salts that are vaporized within an arc chamber. HIDs produce more light for a given level of power consumption than ordinary tungsten or halogen bulbs. Automotive HID lamps are commonly called “xenon headlamps,” though they are actually metal halide lamps that contain xenon gas. The light from HID headlamps exhibits a distinct bluish tint as compared with the yellow-white color of tungsten-filament headlamps.

HID headlamp bulbs do not run on low-voltage direct current; they require a ballast with an internal or an external igniter that is either integrated into the bulb or included as a separate unit or part of the ballast. The ballast increases the voltage substantially and controls the current to the bulb.

FIGURE 39-5
HID headlamp assembly.

HID headlamps produce between 2800 and 3500 lumens from between 35 and 38 watts, while halogen filament headlamp bulbs produce between 700 and 2100 lumens from between 40 and 72 watts at 12.8 volts. The advantage of using HID headlight systems is that they offer substantially greater luminance than halogen bulbs (about 3000 lumens versus 1400 lumens for comparable halogen bulbs). If the higher-output HID light source is used in a well-engineered headlamp optic, the driver gets more usable light. Studies indicate that drivers react faster and more accurately to roadway obstacles when using good HID headlamps than when using halogen headlamps; therefore, good HID headlamps contribute to driving safety.

The contrary argument is that HID headlamps can impact negatively the vision of oncoming traffic due to their high intensity and the “flashing” effect caused by the rapid transition between low and high illumination in the field of illumination. This potential distraction increases the risk of a head-on collision between a vehicle using HID headlamps and a blinded oncoming driver. Scientific studies of headlamp glare from HID systems has shown that for any given intensity level, the light from HID headlamps is 40% more glaring than the light from tungsten halogen headlamps.

Some countries mandate that HID headlamps may only be installed on vehicles (except motorcycles) with lens-cleaning systems (to reduce glare) and automatic self-leveling systems (which prevent dazzling oncoming traffic). These systems are usually absent on vehicles not originally equipped with HID lamps, so if a halogen headlamp is retrofitted with an HID bulb, light distribution with illegal levels of glare will be produced.

Another disadvantage of HID headlamps is that they are significantly more costly to produce, install, purchase, and repair. However, some of this cost is offset by the longer lifespan of the HID burner relative to halogen bulbs.

Light-Emitting Diode

Light-emitting diodes (LEDs) have been used for some time in various automotive applications, such as warning indicators and alphanumeric displays. More recent developments in LED technology have seen the production of a wider range of colors and LEDs that are brighter than previous types. It is now possible to get LEDs that emit bright red, green, blue, yellow, and clear or white light. This has made it possible to use LEDs for many new applications, such as more general lighting applications. For example, LEDs are now often used for stop lights, turn signals, and interior lighting on vehicles Figure 39-6.

FIGURE 39-6
LED lights.

One of the advantages of LEDs is that they turn on instantly. This is particularly useful in brake lights, as they can reduce the braking light response time by two-tenths of a second. This translates to an extra 16' (4.9 meters) of stopping distance for vehicles traveling at highway speeds. LEDs also have better visibility in inclement weather, operate at cooler temperatures, consume less energy, are much smaller, and can last up to 100 times longer, reducing the cost of servicing. LEDs can be specifically designed for LED lighting and also as LED replacement bulbs for more traditional bulb holders.

For automotive applications, a number of LEDs are grouped together to provide the amount of light required for the application. Additionally, LED light lenses are specifically designed with light-focusing prisms and lenses to focus the light generated by the LEDs. A typical LED has a voltage drop of 1.2 to 3.5 volts across it, depending upon the color, when it is forward biased and emitting light.

When used in automotive lighting, many LEDs are required to give off a specified amount of light. To do so they are usually connected in groups called series strings. A number of series strings are then connected in parallel until enough LEDs are connected to give off the required amount of light.

LEDs work best when the voltage to them and the current flow through them remains constant at a preset level. There are two main ways to achieve this; the first is via a resistor. The second and more preferred way is through the use of a voltage regulation circuit.

Some LED lights are multivoltage, which means they can work on both 12- and 24-volt systems. These lights are normally used in aftermarket products, which can be installed in a wide range of vehicles.