Laser lights and sensible light tresspass laws

8 years 8 months ago - 8 years 8 months ago #91463 by cloudsail
BMW is experimenting with Laser car headlights and a recent Sandia National Labs (U.S.) study indicates that solid state lasers can produce light which is perceived as high quality white light, in some cases more efficiently than non-laser light sources.

Incidents of pocket laser misuse, especially those involving motor vehicles and aircraft, have led some countries to restrict or ban lasers (as Australia has.)

We may soon come to a time when amateur astronomer tools such as laser colliminators and laser pointing devices might require a license while streetlights and BMWs are actually shining lasers into the sky without restriction. Since very few lawmakers have an understanding of optics and lighting technology, I hope we astronomers are able to help guide them in making sensible light tresspass laws.

Laser-based white lights have characteristics which could alleviate some types of light pollution:
  1. The emitting source is extremely small, roughly the size of a bacteria while discharge tubes are typically several tens of centemeters long. Small emitters make for easier to focus lights so there will be no technical excuse for such lights to shine above the horizon.
  2. The spectrum of the white light components will consist of a few extremely narrow bands. Could we help the companies select bands which are relatively easy to filter out?
  3. Solid state LASERs, like LED light sources, can be switched extremely fast. There is no warm-up time as with incandescents and discharge lights. This means that it can be used in intermittent applications (e.g. motion sensor lights or street lights which only turn on when there is traffic in the area.)
  4. The fast switch time also means that these lights can carry data. I suggest that we should help design this data protocol:

    • UUID uniquely identifies the light source, useful in cases of light trespass or if lights are misused to shine a driver or pilot.
    • Data (each wavelength (RGB) carries phase encoded data packets

    • Dark intervals so anyone with magneto-optic or mechanical shutters can block out these lights. (e.g. ALL lights using this protocol will go dark for 50 milliseconds every cycle and that 50 milliseconds will be synchronized to UTC)
I know this is alot to talk about in one message but I just thought I'd throw this out for more expert advice on whether any of this is feasible and if so, how do we help rewrite laws which date from an era where gas lanterns were the brightest artificial light sources?

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8 years 8 months ago #91465 by mjc
Very interesting.

I think I can see see where you're coming from - but I don't see it likely that we shall see a movement towards a four-wavelength general lighting standard which is pulsed on a UTC time synchronisation and also carrying identification information to uniquely identify an offending light source is any where near a real probable outcome in any meaningful time frame.

But - if I understand your concept - it is technically doable (and very brilliant).

This is thinking outside of the box.

It means that astrophotography is best done in the time slices when the sky is not illuminated - but these are really short time slices and that means rapid control of shutter or lots of frames and lots of read noise (which do add up - but maybe add up to less than light pollution in some cases - I really don't know).

As I said - thought provoking - but what we need is less light pollution.
I believe that Hawaii only uses low-pressure sodium street lights so that the astronomical community can have a lesser problem in filtering out light pollution (I believe that the astronomical community is number two for income after tourism - but someone can correct me if I'm off the mark there).

Mark C.

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8 years 8 months ago - 8 years 8 months ago #91467 by cloudsail
Thanks for the comment. I agree that we need to start with fewer unnecessary lights and better light and installation. The ideas I present are off in the future and won't be implemented until organizations decide that the cost of maintaining ugly lighting relics exceeds the cost of replacing them. I'm already starting to see this with full-cutoff lights gradually replacing worn-out corbra heads (especially in the U.S.) Someday the last cobrahead streetlamp will be cleared out of a warehouse and the last 500W halogen security light will burn out.

You brought up a good point with dark intervals. 50 milliseconds might actually be too long since people are accustomed to the 10-20 millisecond flicker of discharge lights. I found that some people have experimented with stroboscope filters of 50/60Hz outdoor lighting but since lighting systems are 2 or 3 phase with different lights on different phases, we don't even get 10 milliseconds when all lights are in off state.

I think most of these ideas are technically feasible with existing technology. Even if it's unlikely, its nice to be able to imagine a future with less light pollution. This is also the kind of thing we should start talking about now so that in 50 years we don't have a dozen competing standards (e.g. NTSC/PAL,50Hz/60Hz...), none of which has a standard UUID or dark interval, some of which use 3 or 4 color lasers where chosen wavelengths happen to fall across the Oxygen III or Hydrogen-alpha lines.

I have seen low pressure sodium light ordinances, I think around Lick observatory in California and maybe around Yerkes in Wisconsin. I don't know if astronomy is the number two industry in Hawaii. Until a couple of years ago I think it was selling property to every man woman and child, just as it was here.

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