4WD MODIFICATIONS - ELECTRIC & LIGHTS
Two years ago it seemed that the next big breakthrough in automotive lighting would be laser lights, but that’s not how it’s turned out. Yes, there are some low-cost laser/LED combination driving lights on the market, but quality makers haven’t gone down the laser road yet. We checked out why.
On paper, the laser offers superior beam distance and typical claims for laser/LED combo lights are one lux at 1.6 kilometres. However, that laser beam is very tightly focussed and the LEDs are added to ensure there’s medium-distance spread as well.
In that regard, they’re similar to the ‘hybrid’ lights that combine high intensity gas discharge (HID) distance globes with LEDs. The downside of these types is that HID globes have a finite life, where lasers and LED sources can outlast the life of the housing and lens.
So, does the combination laser/LED light look like the future? Possibly, but there are other issues and the main one is colour temperature. We’ve explained that factor in this Tech Torque story. But, in summary, higher ‘colour temperature’ figures don’t necessarily improve light quality.
When more Kelvin can be too much
Stock halogen bulbs have colour temperature around 3000K-3600K – ‘K’ stands for the ‘Kelvin’ measurement of temperature – giving a soft white light with slight yellowish tint.
Stock HID lights produce 4000K and are are substantially whiter than that of halogens.
Most LEDs have colour temperature in the 5000K-5600K range and the light ranges from cool- to bright-white colour, sometimes with a slight tinge of blue.
People who think blue light is ‘cool’ opt for 6000K+ lights that have a distinct blue tinge.
Lights in the 7000K-8000K range used to be exclusively for vivid area lighting, but now there are automotive LEDs this range. The blue colour is similar to that of some high-intensity street lighting.
Above 9000K the blue colouring in the beam becomes darker and the beam is less effective at illuminating distant objects. Above 10,000K the colour temperature approaches violet, so lights with this Kelvin level are best kept for decorative purposes: puddle lights and under-vehicle lights.
Laser/LED combo – note the bluish laser long-distance beams
The laser lights we’ve seen have very high Kelvin levels, so that’s why most mainstream driving light makers haven’t embraced them. We spoke to some importers, who are monitoring the situation, but remain committed to LEDs at present.
Incidentally, we’ve made repeated attempts to test Kings’ low-cost hybrid laser/LED lights and light bars, but they’ve declined to lend us any for evaluation.
Although we’ve been able to find any top-brand laser/LED driving lights in the after-market, some expensive luxury vehicles are fitted with Osram laser headlights. Dr Roland Fiederling, Application Engineer for Automotive at Osram Herbrechtingen, obliged with an explanation of how this has been accomplished.
Osram’s laser headlight
High beam in the BMW i8 and Audi R8 lights up to 600 metres, or double the range normally experienced with LED full beam, thanks to the laser module developed by Osram that is integrated into the LED headlight. Like some Range Rover models the BMW i8 has ‘smart’ headlights that have multiple light sources that are individually on full beam, or dipped, depending on feedback from the car’s forward-facing camera.
In the laster headlight fitment to the BMW i8 and Audi R8, high beam is activated as soon as driving speed exceeds 70km/h and the on-board camera can see that there is no oncoming traffic.
Laser diodes can generate a lot of light in a very small space and extremely high light intensity enables long range.
The basis for the laser high beam is a development from the research laboratories at Osram Opto Semiconductors. Blue laser diodes with power of at least one watt have only been available for a few years. They are based on indium gallium nitride technology and were originally developed for professional projector technologies.
Osram’s Automotive Laser Activated Remote Phosphor (LARP) development started a few years ago, with the aim of integrating laser lights into automobiles, but it’s not easy to operate laser diodes in vehicles, where they need to function in a temperature window of -40o to +100o C.
As we’ve already seen, laser diodes emit monochromatic light with high Kelvin colour temperature and a wavelength of 450 nano-metres, which is perceived as blue by the human eye.
“This light is unsuitable for use in vehicles,” Dr Roland Fiederling said.
“White light is needed here; preferably with a colour temperature of around 5500 Kelvin.”
Therefore, specialists from Osram Specialty Lighting developed a module in which the laser light from several diodes initially strikes a converter. With the help of a fluorescent substance, this converts blue light into white: exactly as in modern light-emitting diodes.
“However, LARP systems are still expensive and are the province of premium vehicle manufacturers, but the costs will be reduced by increasing volumes,” said Dr Fiederling.
“This can be done by implementing LARP systems in mid-level vehicles.”
Ongoing development will ensure that laster lights become more widespread in the near future, because laser light generates extremely high luminosity, which is far above the brightness of conventional technologies.
The brightness is four times that of an LED and that permits the use of very small optical components that can be arranged as required, thus creating a good deal of design freedom for the light designer.
Powerful laser headlights and driving lights could be fitted into very small spaces, allowing them to brighten our paths, without posing mounting issues or interfering with modern 4WD lidar systems that run collision avoidance and autonomous cruise control.
Watch this space!