Redstone lamps do not emit light.

[Anna Bakker]

The redstone lamp block does not emit any light in renders. Making bright redstone lamps in dark rooms.

Renders of areas using redstone lamps for lighting:

http://imgur.com/tTk3UUC

http://i.imgur.com/8axhSru

Also happens with jack-o-lanterns and beacon blocks:

Jack-o-lantern render: http://i.imgur.com/IS0NpET

Beacon render: http://i.imgur.com/fYoHN8y

However it does not happen with glowstone blocks: http://i.imgur.com/3CCwwDw