Consider also the speed of the
pupullary light reflex. When you have excess light shine in your eyes, you're temporarily blinded and disoriented (if the excess is very large), but the constrictor muscles in your eye clamp down on your iris pretty quickly. "Tactical" lights are really bright, but in a second or two, you can see the source of the light, at least.
However, it takes
three times as long for the iris to dilate once the light is removed. So, if your illumination can blind someone for time T, it ruins their night vision for close to 3T, plus the time they're disoriented from initial flash. If your goal is maximum visual disruption, either because you don't want incoming rounds, or your gun is still holstered, you're doing it wrong by simply shining your light continuously. This physical effect is why higher-end "tactical" lights are starting to have one-button or programmable strobe features.
This isn't intuitive, but if you're not photosensitive epileptic, you can easily try this on yourself in the mirror and compare the effect both techniques have on your vision. Not that I have, of course.
Anyways, that's just my opinion. I don't think seeing my target clearly is more important than avoiding presenting an aiming point, and I like this effect to maximize results from very bright lights.
Because of this, the cost of night-sights or a laser are well worth it, for me. For others, I suspect the value equation comes out differently. Your mileage may vary.
EDIT: The phrase "night vision" is turning into an advertisement link for me. Anyone else seeing that? WTF is that?
EDIT2:
This is precisely what I disagree with. In the lighting conditions I encounter in my daily routine, I have no problem finding light where I could identify an aggressor (either with a handheld light, or by ambient light sources) but lack the contrast to easily acquire my favored black-on-black sights.