Lasers are away of adding intensity to the centre of a headlight main beam, allowing solid-state front lighting to beat ‘xenon’ HID (high-intensity discharge)-based lamps which were continuing to out-shine LED headlamps.
In a laser headlight, a blue laser is directed through a phosphor, resulting in a narrow cone of ‘white’ light.
In the Audi case, there is one laser module per headlight, and within each module are four 450nm laser diodes producing 300µm beams. Post-phosphor, the firm has selected a colour temperature of 5,500K.
The strategy is to add the laser to the main beam to increase down-the-road illumination – in the Audi case above 37mph. A camera based sensor system detects other road users and actively adjusts the light pattern to avoid dazzle.
The A8 LMX is Audi’s supercar, with a 570PS 5.2 litre V10 engine giving 0 to 62mph (100km/h) in 3.4s, and a 198mph top speed. There are only going to be 99 of them, and the UK debut will be at the Goodwood Festival of Speed.
BMW is going to offer laser-enhanced main beam as an option on its i8 car at the end of 2014.
The reason lasers are better than LEDs in adding ‘punch’ to a headlight is light intensity – the term to google is ‘etendue’ if you are keen.
When all the maths are done, if the source emits more lumens than are required, the headlamp can be smaller as the optics do not need to be so efficient – which is largely why HID lamps can beat LED headlamps.
And if the required lumens can come from a smaller original light source, the whole headlight can be smaller – which is why laser lamps beat both HID and LED headlamps on narrow beams.
And why is headlamp size so important? – because styling is ridiculously important in the car world.