[Varyon]

This is a bit complicated, but I feel a combination of Illumination and a modified Obscure may work here.

Obscure would need Defensive, Stealthy, and Selective Effect, for +170%. Defensive means you and those within the area are unaffected by the effect, Stealthy means there isn't a visible cloud or similar when the ability is in use, and Selective Effect lets you insure only allies benefit from Defensive (optionally, this may be extended to allow allies outside of the area to be unaffected by the Obscure). Only working on the light you produce is a pretty significant Limitation, possibly enough for -80%, but let's go with -70% to make the math easy. Always On may be an option, although I'm not certain that's a legitimate Limitation with the above build; if it is, that's another -50%. That means the Obscure is [4]/level ([3]/level with Always On), and you simply need to buy enough levels to reduce the illumination to nothing.

As for "reduce the illumination to nothing," that depends on how you have light sources function and how dark you need to let things return to. The Basic Set rules simply have them reduce darkness penalties to -3 within a set area (either a cone or radius), so if you want this to be able to keep things pitch black (-10, characters are blind without their own light source) you need 7 levels, for [28] ([21] with Always On). The rules from Powers: Enhanced Senses are more complex, but 7 levels will probably still work out alright if you're ok with foes maintaining a bit of sight. To insure they can never see using your personal light source, you have to go with 10 levels (as this automatically drops things to "cannot see"). Otherwise, a very close foe will be able to see a little bit. If you're fine with things just staying really dark, but not all the way down to -10, 5 levels should work well for you, for only [20] (or [15]). Note this is the cost for Obscure - you still need the [1] for the Illumination Perk.