When you mine a powered Redstone Lamp block with a Silktouch enchantment on a Pickaxe, the item drop is a powered Redstone Lamp. (When you place the block it is powered but quickly unpowers).
MC-2775
Silk Touch on Redstone Lamps
Resolved
Duplicate
2
(Unassigned)
Confirmed
lamp, redstone, redstonelamp, silktouch
Minecraft 1.4.4
Retrieved
Confirmed