Throw Me a Frikkin' Bone Here, People

BMW tests ‘1,000 times brighter’ laser headlights

The intensity of laser light poses no possible risks to humans, animals or wildlife when used in car lighting, BMW says reassuringly. The automaker says that’s because the laser light is first converted for use in road traffic, a bright, white that “is very pleasant to the eye.”

Maybe your eyes, but we’re not sure about everyone else’s. Did we mention laser headlights are 1,000 brighter than LEDs. Oh yeah. We did.

Yes, you did. Only that’s not what the BMW press release said. What they do say is

[L]aser lighting can produce a near-parallel beam with an intensity a thousand times greater than that of conventional LEDs. In vehicle headlights, these characteristics can be used to implement entirely new functions. Also, the high inherent efficiency of laser lighting means that laser headlights have less than half the energy consumption of LED headlights. Simply put, laser headlights save fuel.

So the observation is that lasers are 1000 times brighter than LEDs, which gets contorted into the claim that the headlights are 1000 times brighter. But they won’t be using as many lasers as LEDs — the goal is to save on energy use. The bottom line here is that laser diodes are more efficient at generating light than LEDs. You would lose that energy savings if for some reason you simply turn the brightness up to eleven.

A single statistic will make this clear: whereas LED lighting generates only around 100 lumens (a photometric unit of light output) per watt, laser lighting generates approximately 170 lumens.

For comparison, in generating white light the best you can do is about 250 lm/W. Presumably you would be using the same technology (phosphor or something else) to generate the white light, so you have to be more efficient at generating the photons.

The way you do this is by making more efficient use of the light. Laser diodes are LEDs with mirrors at both ends of the material, fashioned from cleaving the material — you get reflections whenever you pass from one medium to another with a different index of refraction. You can enhance or suppress this with the appropriate coating; high-power lasers will have a good reflector on one end of the lasing cavity and an anti-reflection coating on the other. Without the mirrors the light from the electrons spontaneously dropping down from one energy band to another can go in all directions. The mirrors allow for stimulated emission, and that will give you gain for photons that can reflect off the mirror and make another pass (or more) through the material. This means you are wasting a much smaller fraction of the photons to spontaneous emission. If you do something to the facets and interrupt the ability to lase (and I’ve seen this), the device reverts to just being an LED. One shortcoming is that laser diodes generally have a shorter lifetime than LEDs — they are static-sensitive and the coatings age — so for this to be viable there has to be the expectation that the lasers will last for several years.

8 thoughts on “Throw Me a Frikkin' Bone Here, People

  1. Extract the laser module, remove the conversion layer. A 20-watt visible laser is an instantaneous eyeball death beam. The street will find uses for these things – the BMW mile-range retina exploder.

    What will BMW use as a heat sink?

    If “laser headlights” will importantly save fuel, and the US is in deep kimchi versus fuel, and 30 million California motor vehicles are mandated to drive with their headlights on in daylight… my head just exploded.

  2. wouldn’t lasers form a beam too narrow for use as headlights? isn’t it important for the beam to widen as it goes?

  3. I know nothing about this, except from what I just learned from this excellent post. So I don’t know what happens to coatings that makes them “age.” Oxidation? Fractures? Erosion by the light bouncing off them? Can’t there be remediation by some known method?

    Laser lightbulbs could pass through a diffuser like frosted glass or fog to make them safe to the eye. Maybe that’s their highest and best commercial use: fog lights for cars and airplanes.

  4. Coherent laser light usually results in speckle and all kinds of unwanted interference effects. How do they deal with that?

  5. i wonder what color the laser is? probably blue-green with some phosphor coating to convert to a whitish spectrum. or perhaps RGB lasers combined? seems like the color balance would be a problem with differential aging of the individual lasers. (but you cold have a knob to turn and change the color of your headlights!)

  6. @ Wilmot. I’m not sure of the specifics.

    @anders Speckle in the far-field may not be a problem. Laser diodes can have short coherence lengths, and I imagine you can engineer them that way on purpose.

    @ rob I’m guessing blue or even nudging into the UV. Which would explain why this solution hasn’t been viable before now. Blue/UV laser diodes are a fairly recent achievement.

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