Short answer
Buy the Work Light from Wood R Us, open its box, then interact with the placed light and choose the on / toggle-light prompt. On keyboard this is commonly shown as E; on touch and controller, use the on-screen interaction prompt. If you cannot see the control while carrying it, place the light down first.
Turn it on in four steps
Buy the Work Light
Go to Wood R Us and purchase the portable Work Light box. Keep the box in your truck or on your plot so it does not get lost before the cave run.
Open the box
Set the boxed item down and interact with it to unbox the light. The box itself is not the light source.
Place it where you need it
Set the Work Light on the ground or a stable surface. In a cave, aim it at the route ahead before you move; bringing a spare can help if you lose sight of one.
Use the interaction prompt
Move close enough for the object prompt and activate Toggle Light / the on control. Keyboard players should follow the key shown on screen—often E—rather than a vehicle control.
Work Light not turning on?
I am holding it but there is no toggle.
Place it on a flat surface and step close to it. The interaction can be easier to trigger when the object is not being carried or blocked by another item.
Is the Work Light a vehicle light?
No. It is a separate portable object. It will not respond to a truck’s headlight or driving controls.
I bought the box but nothing is bright.
Make sure you opened the box and interacted with the actual Work Light. The packaged box is not the active object.
Do I need it for the secret badge?
It is strongly recommended for the dark cave. The updated secret-badge route can be completed more reliably when you can see the Skeleton and cave path.
Using it for the hidden route?
Once the light works, go back to the full current secret-badge steps so you do not lose time on the old cave-entry method.
Open secret badge guide