Would be fun. However, in open areas such as the walker for "Devil's Lair" or the Phogoth boss, the area would be too large for this to take any actual effect, perhaps dimming the brightness to equal that of the moment before a public event.
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I'm thinking if enemies can see you, you ought to be able to atleast see their eyes, or maybe they'll still be really dimly lit, but lit enough to aim at. The idea is you would really really have to work at making the enemies out visually. It isn't a perfect idea, and it would require a good amount of tinkering to get right, but I have faith in Bungie, they've done well so far!