How bright is too bright? Photon cannon casualties...

[Myself]

I know there are ratings on lasers, specifying that they're eye-safe or not, because the human blink reflex would or would not have time to protect the eye from damage.

How are these ratings determined? I think it has something to do with intensity as compared to the sun's apparent brightness in the sky, since that's what earth creatures' eyesight is "calibrated" to withstand.

Is there an easy formula, whereby one could plug in lumens and lens beamwidth and optic transmission percentage, and come up with a go/no-go answer about whether a flashlight is dangerously bright? Assume "white" LEDs.

Furthermore, if one were building a light that's definitely on the retina-scorching side of the scale, how would one go about making it safer? The first measure I can think of is software in the driver electronics, so it could never turn on above a certain brightness level. To get bright, it would have to start dim and then ramp up in response to user interaction, so the user couldn't be surprised by a blast to the face while playing with the light.

Also, what regulatory agency handles this stuff? Obviously it's not a problem for hobbyists, but if one were selling absurdly bright flashlights, are there any labeling or adults-only sales laws to comply with? Or do those only apply to lasers?