I think there's a subtle difference between
and
creatures.
are creatures which survive in darkness - vampires, creepy-crawlies, etc. In contrast,
creatures are ones which
produce light, like photons (well, technically photons
are light, but let's not quibble) or which are bathed in metaphorical (holy) light, like crusaders. If you have a torch at night-time, the fact that it's night doesn't make the torch less bright, the torch makes the darkness less prevalent.
If anything, light creatures should reduce the effect of Nightfall/Eclipse.