Many years ago I did a lot of work on visibility (not specifically in this area, we were looking at enhancing the chances of seeing trials aircraft and released weapons within danger areas). It is not anywhere near as simple and straightforward as just "fitting a bright light".
First off, we are far, far better at spotting moving high contrast changes than we are at spotting bright colours, lights or whatever. For example, dayglo orange is pretty hopeless at being spotted (except against a very dark background), whereas a large area of black moving on white or grey is excellent (and is the reason that training aircraft are now black, rather than the old yellow or white with red stripes).
Secondly, apparent size, or more specifically the spherical arc of your retina that the object covers, is far more important than contrast, colour or brightness. This is one reason why cycles and motorcycles are far less readily spotted than cars and trucks, we are inherently wired to spot things that are much bigger than us (it's apparently something that goes back to when we were hunters and hunted, where big things moving usually meant potential death!). This is one reason that cyclists and motorcyclists are often spotted very late, when the spherical arc of their image projected on the retina exceeds the size that triggers the "automatic alert dimension" the observer suddenly sees them, as if for the first time.
Increasing the contrast by fitting bright lights helps to a modest extent, but what would be even better would be if you could increase your apparent size. I strongly suspect (but haven't done any testing, or read of any test results) that fitting lights or other high contrast devices at the extreme edges of a bike and rider might well be far more effective at gaining attention than fitting a single very bright light in the centre. What you want to do is make yourself look larger, pretty much as some animals do when threatened by predators.
