How to control a redstone lamp with command block?
Solution 1:
Use two command blocks, one connected to a daylight sensor and one to an inverted daylight sensor. Set them both to repeat.
Inverted:
/setblock x y z minecraft:redstone_lamp
Regular:
/setblock x y z minecraft:lit_redstone_lamp
x, y, and z are the coordinates of the lamp. No blocks around the lamp are required.
Solution 2:
In the current version of Minecraft, you need to use this command
/setblock x y z minecraft:redstone_lamp[lit=true]