A large chest sits under an ornate, crystal chandelier. Several sconces light up the room as well.
|The chandelier focuses light, causing fire damage.
A DC 12 Wisdom (Perception) check allows the character to see that the chandelier is mounted on a rotating gear.
A followup DC 14 Intelligence (Investigation) check reveals that this gear also acts as a gimbal, allowing the chandelier to be rotated and tilted in any direction.
When the chest is opened, a long wire moves the chandelier to a position where the light is focused as a tight beam into the chest, illuminating the contents.
A DC 12 Wisdom (Perception) check reveals a fine layer of powder on the bottom of the chest. A DC 12 Intelligence (Investigation) check reveals this powder to be gunpowder.
After the light has been focused for 1 round, the gunpowder explodes. All targets within 30′ of the chest take 6d6 fire damage and are stunned for 1d4 rounds. A successful DC 14 Dexterity saving throw halves the damage and negates the stunned effect.
The trap can be disabled by simply moving the chest. It requires a DC 14 Strength check to move the chest. It will still focus the chandelier, but without the gunpowder to ignite, will merely be warm light.
Other actions, including extinguishing the lights or altering the chandelier work as well.