An alternative is to require the light manufacturers to label "bike light" only if the light meets certain requirement, such as visibility and mounting system. Anyway, we should not be required to meet a law requirement which is hard to meet due to the absence of requirement warranting the availability of what is needed in order to meet the requirement.
Or you could just buy your light at a bike shop and make sure it fits before you ride.
The existing requirement is trivially easy to meet, you don't need to buy a bicycle-specific light to meet it -- a bungee cord and a flashlight will do.
If you're really having that much trouble with it, seriously, go to a bike shop, that's what they're there for.