Dangerous Lamps do the opposite of Suspicious lamps. These give off light, but does not prevent mobs from spawing and has no effect on mob spawners
To craft a dangerous lamp, you will need:
1x Lapis Lazuli Dye 1x Minecraft Redstone Lamp
Place the above ingredients in the middle row of your crafting table in the following order from the left: Lapis Lazuli Dye, Redstone Lamp (or see image above)
Dangerous lamps require a redstone signal to work. You will see a texture change when the lamp is powered.