Speed strobe recommendation.

Richard,

I work for a company that supports the electric power generation industry. Frequency variation on the grid should be virtually zero, certainly far less than the variation you suggested.
Power generators never bring an off-speed or out-of-phase generator online. Throw a significantly out-of-phase generator online and the existing wattage on the grid would drag it into phase by brute force. That could cause millions of dollars worth of damage to both the generating plant and the grid. No utility ever makes that mistake.

The speed and phase of an offline generator are computer matched to the grid, to tighter tolerances than the number you suggested. Only then is the generator connected to the grid.

Voltage swings all over the place. Noise is rampant. But grid frequency is tightly controlled. If it weren't the entire grid would collapse on a regular basis.

Agree with Speedy9194. My partner made one using Corel Draw, but if we'd known about the one at vinylengine that might have worke too. It seems worth trying, unless $100+ doesn't matter to you.

A cheap fluorescent light is all you need for illumination. (Cheaper is actually better - expensive lights often provide steadier luminosity, which reduces the strobe effect.)