LEDs: The Bright Future of Automotive Lighting

Article By : M. Di Paolo Emilio

Solid-state lighting is an enabling technology in the automotive field which offers new functionalities, greater security, design flexibility, easier integration with control systems and electronics...

Solid-state lighting is an enabling technology in the automotive field which offers new functionalities, greater security, design flexibility, easier integration with control systems and electronics, greater freedom in light design, also allowing each manufacturer to characterize its style and philosophy.

The electronics onboard a vehicle control many functions: some concern the windscreen wiper systems, others the air conditioning system. Power management systems cover not only lighting solutions but also infotainment solutions in order to offer comfort, safe, pleasant driving.

LED technology is constantly renewed through the development of new functions and electronic control systems; modern designing involves not only the source, but also the shape, projection and image of the light itself.

The main reasons for the success of LED technology lie in a cooler colour temperature (typically 5000 K), which gives a more technological and metallic look to the car, in the versatility of its use, which makes it possible to create thin and uniform light guides to further personalise the aesthetics of the vehicle. However, LEDs also offer a greater depth of projection, thanks to the higher light intensity, and consequently, greater safety.

 Power Management

Insensitivity to vibration, long life, high energy efficiency, and the possibility of having a total control on the light source are fundamental factors for LED applications in vehicles. LEDs ease of control also makes them a natural choice for the intelligent lighting system that is able to adapt to the vehicle and environmental conditions. To drive an LED correctly and achieve efficient light output, current control independent of the supply voltage is required.

A better solution for driving LEDs is, therefore, using current control circuits. LEDs generally require a constant current to produce a consistent light output: a LED driver must be able to vary the output voltage to maintain a constant current. The output voltage will depend on many parameters, such as the LED manufacturing process, mold temperature and the number of LEDs in series.

All switching regulators and LED display drivers used in the Automotive industry are AEC-Q100 qualified. MAX20090 is a single channel high brightness LED driver (HB LED) for automotive front-light applications such as high beam, low beam, daytime running light (DRL), direction indicators, fog lights and other LED lights. LMR23610ADDA is a SIMPLE SWITCHER synchronous step-down converter in 8-pin PowerPAD package. It is a 36 V, 1 A synchronous step-down regulator suitable for various applications with a wide input voltage range from 4.5 V to 36 V. Peak current control is used to achieve simple control circuit compensation. NCP3065 is a monolithic switching regulator designed to provide constant current to power high-brightness LEDs. The device has a wide input voltage up to 40 V to allow 12 Vac or 12 V dc operation.

Figure 1: block diagram of MAX20090

LED Solutions

A car headlight is a high-tech lighting device with a very important role in terms of design and safety. LED technology offers completely new solutions, with a lifetime being equal to the life of the vehicle and it consumes about one fifth of energy compared to other solutions providing lower fuel consumption and carbon dioxide emissions.

The concept of interior ambient lighting has become popular in recent years with the monochromatic colour, such as orange, harmonizing the luminance level between the interior of the vehicle and the external environment, thus reducing driver fatigue during night driving.

RGB static lighting, which began in 2010, provides an atmosphere which delights the passengers. This was followed by the demand for dynamic lighting effects for different scenarios, such as the welcome light effect when entering the vehicle and the driver’s warning light during emergency situations, such as pre-collision warning and blind-spot sightings.

The RGB ambient lighting project is complicated and expensive. It requires high investment in measurement equipment for calibration, manufacturing and testing. Designers are always faced with the challenge of varying the mixed colour rendering of RGB LEDs. This is caused by variations in intensity and wavelength within the color and brightness groups, as well as dependence on forward current and temperature.

In this context, DOMINANT offers a solution to this with a new family called seddLED (Smart Embedded Digital Driver LED), a digital LED in the world that combines RGB LEDs, LED drivers and advanced communication link integrated in a single package.

Figure 2: seddLED (Smart Embedded Digital Driver LED)

“From the concept car design we might see that lighting in car seat cushion, roof lighting, full ambient lighting and AR HUD will be the future trend in the car. Car body lighting, car to car or car to pedestrian communication display or signage projection lighting could be soon available. These new trend will soon be realized especially when autonomous vehicles getting more popular, “ said YY Lim, marketing director at DOMINANT.

seddLED3.0 consists of full digital RGB color and brightness control via software and is pre-calibrated to D65 white point with an accuracy within 3 SDCM steps at 1,400mcd. In addition, it offers a 2Mbit/s half-duplex differential control bus, fast refresh rate of 52.5µs per LED (5.25ms per 100 LEDs). Its built-in temperature sensor allows it to perform automatic temperature compensation in real-time and comes with self-diagnostic functions.

The package also provides superior corrosion resistance with Au lead frame and is certified in compliance with the automotive AEC-Q100 and AEC-Q102 standards. seddLED3.0 offers greater design freedom to create different atmospheres in the passenger compartment.

Figure 3: Comparison of the colour range between standard RGB LEDs and A3A-FKG-RGB-1. A3A-FKG-RGB-1 with pre-calibrated True Green & Blue have an excellent and stable colour gamut.

In the market we can find Nichia and Infineon who have created a design for a high definition (HD) lighting device with over 16,000 micro-LEDs for front lighting applications. Unlike current HD solutions, the new device provides high resolution light to the driver’s entire visual field.

Daytime Running Lights represent perhaps the most common use of LED technology in the automotive field: thanks to the versatility of the small size of the sources and the high luminance, LED systems make it possible to create optical solutions that can be easily integrated into car headlamps.

OSRAM is also constantly focused on the automotive sector with LEDriving® lamps for both the interior and exterior of the car, offering a complete range of both projection and signaling. For projection lamps, the HL family (low beam and high beam) and the FL family (fog lamps) are available to match the complete range of signal lamps (SL). LEDriving® HL for low beam and high beam replace H4, H7, H11, HB4 halogen lamps.

The use of close-up multi-chip LED sources and total reflection allow precise cut-offs (clean cut-off between the light and shadow zone) and a marked reduction in diffused light, all to the advantage of depth of illumination and glare reduction.

The most advanced solutions in LED technology for front lighting are based on Matrix LED systems, i.e. dynamic LED arrays capable of providing automatically adaptable depth light, so as to prevent glare from vehicles coming from the opposite direction.

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