How to get rid of light pollution?
An idea how to do it with synchronized street lights

Content:

1. The idea
2. Synchronized Light
3. Synching problem
4. Synchronized shutter
5. Needed research
6. Conclusion

1: The idea

First draft: Mars 2015, Last update: November 25, 2015

We all know about our planet's light pollution problem, light pollution hide the stars for us. Especially a problem for us who are interested of astronomy. This is not a DIY project, much bigger and just an idea from me how to solve it.

My idea is to control the street lights with pulse width modulation. If the cameras shutter is synchronized with the gap between the light pulse then the camera will only see a dark background where we have the starlight. Yes, a lot of engineering has to be done, but some parts are almost there.

I have to develop this idea further, but this is how long it has come to date.

Here is a drawing how it works:

2: Synchronized Light source

First we have to synchronize the light source. It sounds complicated but now a days we are replacing the old technology streetlights with LED lights, they are very easy to pulse width modulate. Some of them already has a similar technology built in to regulate the power, just ad an synchronous device.

The speed of light sets a limit of how high the frequency can be. Far away coming light pulses are delayed and will not be in sync. Even more far away light will be damped by the inverse square law, 1/r^2.

With a frequency of 500 Hz and pulse relation 1 to 5 a pit of blackness will be created where you stand with a radius of 60km which is a rough estimate how big the black pit has to be. Maybe it can be more narrower and then we can have a higher frequency, some technical problem is easier to solve with higher frequency.

We are not only limited to streetlights, household lights can have this future also. Moving object like car's lights will be more difficult to synchronize.

3: Synching problem

The clock pulse to synchronize it must be taken from somewhere, maybe GPS satellites can be used? A receiver on the power transformer from high voltage to low voltage grid. The power transformer station can then send out sync pulse over the low voltage grid. That's a technology we have used for years for communication over the power cables.

4: Synchronized shutter

This will be the part that's not so easy to solve with todays technology. If we had been working with a lower frequency as we have in the old days film projectors - 24Hz, we could have a simple rotating disc with holes that synchronizes with the light pulses. But with higher frequencies it's best done with some fast electronic device.

Maybe there is some technology from high speed video cameras that can be used or the new sensor from Invisage: http://www.invisage.com/. If I understand it correct they say the sensor can block or interrupt the incoming light.

It should not read out the signal for every pulse, just collect them. Otherwise the readout noise will be to high with todays technology.

5: Needed research

There is of course a lot of research that has to be done. Here is some areas:

1. Lights are powered from alternate current, energy most be stored enough for every light pulse, high frequency - less energy to be stored, where is the practical frequency limit?
2. Power grids sensitivity to current that pulsating
3. Human sensitivity to flickering light, normally lower than 100Hz
4. How big area has to be in sync to give blackness?
5. Are GPS satellites a way to distribute a master sync, or other alternative?
6. A synchronous camera shutter, what technology today and in future that can be used?
7. Ideas how to use this in other areas to encourage it to be a reality

6: Conclusion

Maybe not a very big technological problem, more political to invest this in the infrastructure. It must be some more use of it to convince the politicians. And because we now are replacing the old streetlights with modern LED technology now is the time to do it.

Imagine what a revolution this will be, you don't even has to use a telescope. Just some active glasses similar to what we have today to 3D television, just a bit more developed to let through more light. Wearing this it could maybe be possibly to see Milky way even from the most light polluted city with synchronized lights.

What more use can we have of it?

Think about it, if we have all lamps synchronized all over the world, then we have a very big flash light that we can modulate the light output something like a Morse code message (you have to take into a account the limit of light speed so they all are in sync). And it will not be visible if you just look at the streetlights. Maybe not so wise because Stephen Hawking has warned us to tell "everyone out there" that we are here.

More ideas must come how to use it to convince the politicians to invest in this.

Stockholm University and Dark Sky association informed, NASA and SETI next.

Update:
Now (2023) they have done some test with this technology in the mountains of Caucasus: A simple streetlight hack could protect astronomy from urban light pollution