Could you make a dark period long enough to mask the multipath variance among emitters and observers? Or would this dark period be so long as to cause annoying flicker?
The wavelength of the control signal doesn't seem relevant.
A 150Hz blink rate means a period of 1/150s, or ~6.7ms.
The speed of radio signals through air near the surface is a bit lower than c, let's call it 299,250 km/s. [0]
When you multiply those numbers you get ~1500km. That means each 'on' and 'off' signal is 1500km long, moving near c. More specifically, the signals are concentric rings around the transmitter 1500km in width.
Let's look at London. I picked it at random, but it just happens to have a land area around 1500km^2. Assume the transmitter is in the center of the perfectly circular city, that means it takes 3.3ms for each 'on' and 'off' signal to cover the entire city. Each on and off pulse is just about exactly long enough to cover the entire city.
All that together means that at any given moment 50% of the lights in the city are on, and the other 50% are off. That's about as far from synchronized as you can get, really.
Also, light is slightly faster than radio in these conditions[1]. The light reaching the center of the city won't be pulsing in the same phase as the signal you're sending out. It will also be blurred and muddied due to the difference in signal speed. You probably wouldn't see much flicker in the light at all, as 50% of the lights are always on. On average, you receive 50% of the light you would otherwise, but that value will never reach 0. There won't be any periods of total darkness where you can make an observation, as the article suggests.
Moral of the story: light (and radio) is much, much slower than most people realize.
[0] https://ieeexplore.ieee.org/document/170108 [1] I couldn't find a confident number in my 16 seconds of searching. Seems like just a few percent faster, but the real number doesn't matter here.
Bonus: you can synchronize the streetlights exactly, but it's much more expensive and complex than a single radio transmitter. You need to have every single light contain a receiver with an accurate clock that synchronizes with a geosynchronous satellite with an atomic reference clock. Search for "GPS disciplined oscillator" if you're curious.
Um am I really really tired and not reading correctly, or is this confusing linear area with square area? London doesn't stretch from New york to Florida.
186000 miles/second * pulse of .003 = 558 miles ~= 900 km
Either way, propagation delay is a huge problem with synchronizing systems. It's not something you usually think about
Better solution is less lights, or turn them off at night or any of the other solutions we've been talking about for 30 years. Remember when street lights were killing sea turtles?
The physics of radio wave propagation are surprisingly complex. Buildings and objects in the path between transmitter and receiver can cause various interference effects that basically slow down the signal. I'm glossing over a lot, but it would take significant effort to precisely measure the exact delay between any one receiver and the transmitter. It's much more complicated than just the distance, and each one has to be measured individually.
I'm not an expert in RF, but I think this concept of a single synchronizing transmitter just doesn't work in the real world. You'd probably build a cell network with many transmitters covering small areas. Each transmitter has the hardware to synchronize with thr others, and the lights just have a simple circuit slaved to the transmitter clock.
There's probably more clever ways to synchronize signals over long distances, but RF is black magic to me.
FM Radio stations have managed to accomplish getting the speaker in your car radio to "blink synchronously" according to a complex signal pattern in the exact same way as millions of other radios simultaneously.... for about a century now. As long as all streetlights are in locations with good radio reception (which, since they're all on streets and are tall, is likely), it would not be that hard to implement in principle a central FM or other radio signal that oscillates according to the expected blinking. Lights that are engaging in dimming could multiply another signal by the central signal to diminish it even more.