Darkness TrickSource Ultimate Intrigue pg. 81
You can manipulate the luminescence of magic weapons.
Prerequisites: Use Magic Device 5 ranks, ability to cast darkness.
Benefit: When wielding a magic weapon that sheds light or that features a luminescent quality, such as a flaming or brilliant energy weapon, you can deactivate that illumination as a swift action. You can reignite the illumination at any time as a free action. Any intrinsic magic properties that would force the weapon to shed light, such as the extra damage of a flaming weapon, do not function while the illumination is deactivated, and the “significant portion” of a brilliant energy weapon that is normally made of light ceases to exist.
If a weapon affected by this ability ever leaves your possession (for instance, if you drop the weapon or pass it to another creature), its illumination and related abilities instantly return.