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Headlamp performance has improved drastically over the past few decades. We investigate the different technologies available today...
Can you believe there was a time when headlamps were optional on vehicles? Not that they were of much help, anyway: early versions (powered by candles, oil or acetylene) were feeble. Today, we take night driving for granted thanks to great lighting tech but innovation in this field hasn’t stopped. If you undertake a nocturnal journey at the wheel of a classic car, you’re bound to appreciate the value of modern illumination. Let’s compare headlamp technologies.
What is light?
Light consists of bundles of electromagnetic radiation known as photon particles. Visible light has a wavelength of around 400 to 700 nanometres, which fall between the infrared and ultraviolet spectrums. Colour temperature describes the colour radiated by an ideal black body and is measured in Kelvin. The orange flame of a match is rated at a colour temperature of 1 700 K (1 427 degrees Celsius), whereas daylight is rated at 6 500 K (6 227 °C). The speed of light is around 300 000 km/s, so it’s unlikely a vehicle would ever be too fast for its headlamps!
Reflector versus projector headlamps
There are many possible sources of light but reflection is the most common method to control beams emitted by headlamps and prevent glare from blinding oncoming traffic. Light is therefore reflected from the surrounds towards the road in the desired pattern. Only about 45% of the light produced is useful.
By contrast, a projector-style headlamp adds a lens that helps to focus the light and project it onto the desired areas on the road ahead of the vehicle. It is possible to add a shield to include the main and dipped beams in a single projector headlamp.
Different light sources
These are the four most common forms of automotive lighting used in headlamps. The figures are for a single headlamp consisting of a high and low beam.
Halogen
A bulb with glass envelope (similar to the household item) operating on the incandescent principle. Usually, a tungsten filament is employed in the glass housing filled with a mixture of an inert gas (like argon) and a small amount of a halogen (as listed on the periodic table, such as iodine or bromine). The “halogen cycle” redeposits the evaporated tungsten back on the filament, which prolongs its life and keeps the glass envelope clean. This results in the production of constant light throughout its operating life.
It’s cheap, simple tech that is easy to replace.
- Yellow (3 200 K colour temperature)
- 55 W
- 1 200 lumens
- 100 metres
- 1 000 hours
Pros: Cheap (R200 per bulb); simple technology; easy to replace
Cons: Energy wastage, as it runs very hot (the gas inside the glass envelope heats up to 200 °C, with the tungsten filament at more than 2 000 °C)
HID (xenon and bi-xenon)
A high-intensity-discharge (HID) headlamp is also known as a xenon unit. It employs a similar type of technology as found in household tube lighting. There is no glowing filament (as in halogen lights). Instead, a high-voltage arc between two electrodes is used to excite the gas mixture in the glass tube. Interestingly, only a small percentage of xenon gas is used in the (mostly metal-halide) lamp to speed up the start-up process. The lamp needs to reach optimal operating temperature before constant light is produced. Bi-xenon refers to a single xenon headlamp with a moveable, internal shield to produce both high and dip beams from a single light source.
White with a blue tint (4 500 K colour temperature)
- 35 W
- 2 800 lumens
- 200 metres
- 2 000 hours
Pro: More efficient and powerful than halogen bulbs
Cons: Takes a few seconds to reach full brightness; more complex and costly than halogen
LED
The light-emitting diode (LED) produces light by electroluminescence, which is based on quantum theory. It involves semiconductors with electrons moving from a high-energy state to a lower level and releasing energy in the form of photons (light). Interestingly, the light produced is directional, thereby eliminating the need for a reflective element, which results in a smaller headlamp. Compared with halogen, little heat is dissipated, presenting a problem with temperature build-up on the LED chips, especially in high-power applications. To compensate, cooling measures or heat sinks must be implemented to prevent damage. LEDs are commonly used for daylight-running lamps because their lower power outputs mean no cooling measures are required.
White (6 000 K colour temperature)
- 30 W
- 3 000 lumens
- 300 metres
- 50 000 hours
Pros: Efficient (100 lumens per watt); powerful; compact; long service life
Cons: Expensive (R59 480 per unit for a BMW i8, for example); complex cooling requirements
Laser
No, lasers are not actually pointed at the road ahead in the fashion of a sci-fi ray gun or phaser. Rather, mirrors focus blue lasers onto a lens filled with yellow phosphorus. The reaction that follows produces intense white light reflected onto the road. Currently, laser lights (used mainly for high-beam applications) are employed in conjunction with one of the other lighting technologies (usually LED) to cater for low-beam operation. Laser lights are used together with LEDs for low beam.
White (close to daylight at 6 500 K colour temperature)
- 18 W
- 3 100 lumens
- 600 metres
- 10 000 hours
Pros: More efficient than LEDs (up to 170 lumens per Watt); compact
Cons: Extremely expensive (R103 444 per unit on a BMW i8); high beam only
Headlight legislation
Why do all modern cars have a pair of headlamps? The reason is legislation (Federal Motor Vehicle Safety Standard, or FMVSS, in the US; European commission for Europe, or ECE, in Europe) specifies each detail of vehicle lighting. This includes position, functionality, brightness and even the icons used on the instrument cluster. The US regulations are more conservative than those in Europe (from a technology and brightness point of view), resulting in the delay of laser light and digital matrix (where the permanent high beam illuminates only selective areas to prevent glare) technology reaching the North American market.
The future of headlamps
Light-source tech will keep advancing but the major area of change in headlamps will concern the control of the light beam. For example, when Mercedes-Maybach released its facelifted S-Class last year, it incorporated Digital Light. The high-beam quality LED light source shines through a mirror array comprising more than a million units. In effect, the headlamps become a HD projector with full control over the light beam. Oncoming vehicles can be “cut out” from the beam to prevent their drivers from being blinded, which eliminates the need for low-beam functionality.
Another possibility is to project traffic signs on the road that may warn other vehicles, create a pedestrian crossing for people who want to cross a road or even project arrows to help with navigation. Microprocessors, control algorithms and calibration are crucial for these type of headlamps to function effectively. Unfortunately, the advancement in technology will also increase the cost of headlamps, which does not bode well for new-car prices (or insurance premiums).
Headlamp milestones
- 1898
The first electric headlamps are introduced on the Columbia electric car.
- 1912
Cadillac integrates its vehicles’ electrical ignition and lighting systems (the lights were separately powered by a battery before).
- 1915
The Guide Lamp Company introduces the first “dipping” beams, now more commonly known as low beam.
- 1917
Cadillac introduces the first lever-operated low beam. Before, the driver had to stop and manually adjust the lights.
- 1924
The first bulb (Bilux) capable of emitting light for both low and high beams is unveiled.
- 1927
The first foot-operated dimmer switch reaches production.
- 1933
Packard launches tri-beam headlamps with three filaments and three modes.
- 1934
Directional lighting is introduced on the Czechoslovakian Tatra 77.
- 1936
The first hidden headlamps (pop-up lights) debut on the Cord 810/812.
- 1947
The world’s first steering-linked lighting in the Tucker Torpedo launches. The Citroën DS makes the technology famous in later years.
- 1991
First xenon lights in the BMW 7 Series.
- 2007
First LED headlamps in the Lexus LS600h.
- 2014
First laser headlamps in the BMW i8.
Original article from Car
