LEDs Brighten the Future of Automotive Lighting

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For years now, LED technology has been gradually finding its way into automobiles. LEDs have become brighter, more efficient, and less expensive. Automotive lighting has made driving safer, but it’s introduced some sophisticated and complex electronic changes that create challenges for designers. Let’s take a look at automotive lighting basics and the latest developments impacting design.

Why Use LEDs in Automotive Applications?

There are two major rationales. First, LEDs are more efficient than the older incandescent bulbs. They consume less power for the same or greater illumination intensity. Evaluations indicate that LEDs are six times more efficient than the incandescent bulbs they replace.

Second, LEDs have a longer service life than an incandescent bulb. Headlights, tail lights, and others burn out after 1,200 or more hours of operation. And replacement is usually expensive. The average LED has a lifetime of 42 times that of an incandescent. With a service life of over 50,000 hours, you may never have to replace a light source in your vehicle.

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• 120W matrix-compatible headlight electronic control unit (ECU) reference design
• Flexible configuration of LED drivers
• The three trends influencing rear lighting systems

Automotive Lighting ABCs

You can divide automotive lighting applications into three categories: exterior front, exterior rear, and interior. This article will focus on exterior lighting. Front exterior lights include headlights, high and low beams, daytime running lights (DRLs), fog lights, and turn signals. Some vehicles also feature adaptive headlight lighting that enables better illumination around curves while driving in low-light conditions.

Rear lighting consists of tail lights, stop lights, backup lights, and a license-plate light. And there may be other decorative or style lighting depending on the manufacturer. In any case, with a full complement of front and rear LED lights, power consumption can be high. But that turns out to be less power than what’s consumed by older incandescent lights.

Automotive lights are individual LEDs grouped together to form a matrix or cluster. Most automotive LEDs are white, but red and amber are also available in different sizes and light intensities. Light guides, lenses, and diffusers are used to make the light appear as though it comes from a single source, eliminating the individual dot look of the early LED automotive light fixtures.

Special drivers are needed to operate the LEDs. One driver IC can typically handle a cluster of multiple LEDs. The drivers are current sources with appropriate drive and interface circuits. The typical arrangement is a series string of LEDs, so that all LEDs receive the same current. This is essential to ensure the uniform color and brightness of the lights.

LED drivers are essentially dc-dc converters/regulators. They operate from the car’s 12-V system and provide either a lower or higher dc output as required. Buck and boost types are common as are buck-boost, SEPIC, and Cuk. The drivers connect to a master control MCU, and a CAN interface network is provided to route the control signals around the vehicle as needed.

Front and Rear Lighting

Front lighting is generally fixed and similar on all vehicles—headlights, DRLs, and turn signals are all mandated and standardized. Special drivers are required, of course. The newest innovations include dimming and adaptive front lighting (AFL). Dimming, used to prevent blinding oncoming vehicles, is accomplished with pulse-width modulation (PWM).

AFL consists of two additional lights, generally to the left and right of the headlights. These lights provide extra side illumination for making turns safely at night. As the steering wheel begins its turn to the right or left, the AFL units turn on and move to direct the light to the side. Stepper motors are commonly used for this purpose. Up and down movement can adjust the lights so as not to interfere with oncoming driver vision.

The story is different with rear lighting. While tail lights, stop lights, and backup lights are required, the rear of the vehicle has become an open territory that manufacturers can explore with new designs. Vehicle makers like to create a unique look or symbol that designates a particular make or model. Some vehicles may sport a signature look implemented with a creative light presentation or operation. A current trend is lighting that extends across the entire rear of the vehicle.

Rear lighting is getting more interesting as manufacturers want pixel-level control where a pixel is one LED, which would enable a variety of tail-light animations. Newly available drivers provide for this capability. Three trends are influencing rear-lighting systems: complex animation, evolving lamp styles, and diagnostics. Consider the following links to learn more.

The Auto Lighting System

Equipment that makes up the older traditional lighting systems of vehicles consists of the body control module (BCM) and the LED drivers (see the figure, a). The BCM is a block of electronics with a microcontroller (MCU) base that operates all or most of the various electrical and electronic systems associated with the body of the vehicle, such as doors, windows, mirrors, seats, and lighting. The BCM operates the individual light drivers.