As LEDs improve in brightness, they are offering many benefits in the automotive world. Having hung on a step ladder in an icy truck lot while changing filament bulbs on over the road trailers in a Siberiacuse winter, I understand the advantages all too well. The filament bulbs were subject to failure due to road vibrations as well as fusing during the rapid temperature changes when applying current during a period of extreme cold. Other advantages include color control as well as light dispersion. LEDs don’t have to heat up either so the light is immediate.
Along with the LEDs, there has been a large entrance into the LED driver market as well. The basics of the drivers are to control the LED current to maintain a certain brightness. I said current not voltage for the recent distribution Applications Engineer who couldn’t get it right. In reality, the current keeps the LED happy for longevity as well as color by setting the current level. The brightness is then adjusted using pulse width modulation or PWM. This is nothing more than an averaging pulse that controls the light ON time or duty cycle in relation to a total period or frequency. The frequency is set to a level so that it doesn’t appear to be flashing to the human eye.
There are many ways to classify automotive LED lights and drivers. Texas Instruments classifies their drivers by location by grouping them into Exterior Lighting, Interior Lighting, and LDC backlighting, infotainment, and cluster. Allegro Microsystems has an informative diagram for their automotive LED driver products.
There are other ways to look at the automotive LED market. Classifications can include illumination, marking and warning lights, backlighting, and theatrical or accessory based. Among these markets are both OEM and aftermarket opportunities.
The basic automotive exterior lights include headlights, daytime running lights (DRL), and the marker and indicator lights such as tail lights, signal lights, and marker lights. While headlights address illumination in order to see, the others involve marking the vehicle or indicating direction in order to be seen. These products can provide advantages in brightness over the older filament products. They can also use a technology that produces a certain wavelength and color thus enabling a clear lens. This can allow for adjustments based on local laws such as the need for yellow signal lights on the rear of European vehicles (whereas the US can use red). The aftermarket for signal lights has caught more than one person wondering why their flash rate changes due to flashers that depend on current draw.
Headlight retro kits are touting 6000K of ultra-bright white light with ranges from 30 to 80 watt power consumption. Lifespans are “claimed” to be anywhere from 30,000 hours to 50,000 hours. The advantages include a wider light pattern and less heat generation than their halogen and Xenon HID counterparts. These LED headlights do dissipate heat and therefore include an internal heat sink and powered fan arrangement. Still, this heat can’t be used to keep ice and snow from building up on the lens. Boss snow plows have solved this problem with their Ice Shield Technology which “utilizes a thermally conductive grid to heat the SL3 lens”. Some of the headlight retrofit kits offer an adjustable color feature for use as a fog light with yellow color.
LED headlights are not always the answer according to Popular Mechanics. In their article titled “Problem of LED Headlights” they discuss issues. Personally I didn’t read it as they require an email to do so. As a result of this privacy intrusion, there is not hyperlink to the article yet I did acknowledge it in the References.
Interior lighting is also becoming a large market. Through the IC drivers, intelligent control can be integrated in to illuminate specific areas or offer features such as theatre light dimming. On Semiconductor takes it one step further with a product that enables LIN (Local Interconnect Network) control of red-green-blue (RGB) that can create over 16 million color combinations. The device is said to be design friendly and programmable via a USB based application circuit.
Intelligence in not limited to user or condition control. Allegro Microsystems is integrating Hall Effect Sensors into their LED driver IC products in order to switch on lights when doors are opened. Similarly, some headlights have built in sensors for dimming during periods of oncoming traffic.
Back lighting of displays is an important aspect of vehicle technology. As conditions change between daylight and night darkness, backlight adjustment is key to driver vision. Many of the drivers for this application have little features such as eliminating “night flash” while starting the car.
Aftermarket lighting and emergency lighting expand both driver and LED opportunities further. Low profile emergency lights reduce wind resistance thus improving fuel mileage. Integration is also easier as is lighting control using intelligent driver ICs. Offroad, fog, and reverse LED lighting solutions are becoming popular among automotive enthusiasts. Even logo and sign lettering are projected using LEDs in vehicle applications.
The LED market is speculated to be in the billions of dollars. No solid figures were provided for the overall market during an internet search however the market will grow as car sales grow and applications increase. No doubt there will be an increase in the number of features and solutions for improving automotive lighting and enabling new applications. When I wrote my synchronous application note AN1520 twenty three years ago, I didn’t focus on the low voltage LED potential like I did digital applications. Surely, the low voltage of LEDs expands the opportunities as does stacking LEDs offer opportunities for other topologies. For Planet Analog engineers, LED lighting creates a bright future in more ways than one.