Per a quick search, 500mW is the threshold where a laser can start doing damage faster than your blink reflex and reflections are also dangerous (IIRC this is the bottom end of class 4 lasers). Most of the projects I’m finding online that are similar to this one are around 1W, so double the threshold.

That’s not necessarily the “instantly blinding” territory I suggested, but even a short exposure will cause damage.