As mentioned in BigJack's thread, I reckon this idea has enough traction to get another thread and feline herding attempt.
The Problem: Some of us are unsure of how effective our hi-viz and rear lighting is, others are unsure if their front lights are too bright, especially on off-road paths. Also: both.
The Solution: We, ah, kill the Batman.
Okay, the Actual Solution: We meet in a city(provisional candidate: Edinburgh), swap hi-viz and bikes, then ride towards each other from a reasonable distance along an off-road path. This means dynamo-lit persons can see their LEDs emitting in anger.
We also have at least one car present. I imagine insurance issues might make it impractical for anyone but the owner to drive it, but sitting in the passenger seat(maybe even the back) ought to give a functionally equivalent experience of seeing how your lights and reflectives look from behind the wheel.
At the risk of looking really lazy, I think Harrison Park is a pretty good spot. There's an inky stretch of canal just west of it, and the block I happen to live in has a good quiet street that's amenable to the car test, in that with a lookout at the top you can safely* reverse back up it to repeat that part of the testing conveniently.
It might turn out that simply sitting with the lights on while your bike model rides round you tells you everything you need to know so that may prove moot.
*if that's not legal, it's a small block, so doing loops isn't too silly.
The Date: I will say Monday the 3rd since the weather is forecast as good then and poor Tuesday. The time, if we choose Harrison Park as the venue, is pretty open-ended since I'm a sad bike obsessive with Tron nostalgia and no life so I'd be happy to malinger in the park taking long exposure light-trail photos of people doing this for around two hours. Any time from 6.20 onwards suits.