The Lamp is a decorative light source block. To it turn on, it must either be placed on a Bedside Cabinet or be powered by redstone.
When a Lamp is turned on while placed on a Bedside Cabinet, it will send out redstone signals from all sides of the bedside cabinet and underneath the cabinet also. This could not be used to make a secret door as such.
The textures the lamps uses are white wool to represent the lamp shade and obsidian for the stand.