An alternative approach to combat light pollution?

[chiltonstar]

In an area where most polluting lighting is from sodium or sodium/mercury lamps (like where I live for example) which are gas discharge that turn on and off with the phase of the applied current modified by a choke, are the lamps sufficiently in-phase that a rotating light chopper or Pockel cell could selectively filter out the parts of the phase where the lamps are "on" leaving the relatively dark part of the cycle? Might be only a partial solution, but I wonder if it would improve sky contrast in some cases? Experts?

Chris

[SeedyF]

That just makes me go too

[Shibby]

It's a nice idea I'm not expert, but I did find this video:

YouTube - LAMPS/LIGHTS at 1200 FPS -high speed camera -EPILEPSY WARNING!

I'm not sure they're ever off long enough for that to be viable, in fact they're never totally off. Also, I doubt all the lights in a city are in phase with each other! (maybe I'm wrong here) I really like your lateral thinking though!

[E621Keith]

It might work if there is only one street light, but there are a lot of them in a city. The phase differences between individual lights probably means when one of them is OFF, others would be at different stages of ON.

A light pollution filter seems like a much cheaper and easier option.

[yesyes]

I like the thinking here. Though I'd have to agree that they are not all in phase. They are probably fed by a 3-phase feed and then every 3rd lamp on the same phase.

[yesyes]

if someone had a 1200fps camera (or something in that region), they could try recording several lamps down a street or so and see if they are in phase.

[yesyes]

Actually, it needn't be as expensive as I thought. This one does 1000fps:

Casio Exilim FH20 Ultra High Speed Camera 20x Optical on eBay (end time 15-Nov-10 16:20:11 GMT)

[darkly]

They're all different distances away from source so there will be a time difference between each light - I fink!

[Helen of Troy]

Thanks darkly, I have just bought 'Turn left at Orion'.

[darkly]

Thanks darkly, I have just bought 'Turn left at Orion'.

I hope you enjoy it, it's still my favourite, especially with winter starting, soon as I get home - first clear night I'll be using it.

Come to think of it I could probably use a new copy, red wine, brandy ... they all leave stains you know.

[yesyes]

They're all different distances away from source so there will be a time difference between each light - I fink!

Not at 1000fps.

Light and electricity travel at the speed of light; 300000km/s. So in one frame at 1000fps it travels 300km. Even in the worst case if the electricity feed is on your side and travels away from you, the lamp would have to be 150km away to notice the difference.

[darkly]

Not at 1000fps.

Light and electricity travel at the speed of light; 300000km/s. So in one frame at 1000fps it travels 300km. Even in the worst case if the electricity feed is on your side and travels away from you, the lamp would have to be 150km away to notice the difference.

Yup, but I think we've crossed our wires here (no pun ) Physical systems are not perfect theoretical systems.

There are all sorts of losses and bottle necks in these systems, I've worked on systems with a mix of fibre optics for pictures and twisted pairs for signal data / switching, maybe down 2km of cabling, I can flick a switch and notice an appreciable time delay in a light coming on or off.

I've seen the same thing in large rooms when you flick the light switch the lights at the far end come on slightly later, small but noticeable difference, shurely, if the electrons were freely moving at c then it would be too fast for us to notice.

So, any frequency would be time delayed ever so slightly the further down the circuit the sine wave went, like a ripple.

Could be well wrong but that's always the way I understood it from the original hole theory I was taught. But, I could also introduce you to people who would say I was wrong so, 50/50.

Come to think of it, that's another good point, 150km of wiring for a city's street lighting is nothing compared to what's down there, I never thought about it before, but, your average UK city must contain thousands of km's of wiring just for its lighting alone, never mind power supply, comms etc - the quantities must be staggering not to mention other issues such as losses due to volt drop etc.

That's a new one for me to ponder on.