UPDATE 10/4/20: Uploaded STEP files for the bracket and retainer piece. You can attempt to modify these in your CAD software if your light bar measures differently than the one I designed this for.

UPDATE 2/16/20: Uploaded an improved version and plates to hold the light in place. I made the mounts more sturdy and slightly shorter to minimize vibration.

This is a mounting bracket for an LED bar to the Prusa i3 MK3. It clears the extruder at the max z height and gets the light pointed back at 20 degrees. It can also be used for an 8mm LED strip (if you print the adapter for it). The bar i purchased is about 305mm long and 15.5 x 15.5mm wide and runs off of a 5v 1amp USB power supply (wasn't included, used one from an old phone). Here is the link:

https://www.amazon.com/gp/product/B075WQNY6W/ref=ppx_yo_dt_b_asin_title_o01__o00_s00?ie=UTF8&psc=1

To mount the bar you just need to print two of the brackets and two retaining plates Use two small M3 screws threaded through the holes at the end of the brackets to hold the LED bar or strip adapter in place with the plates.

You could also print two of the LED strip adapters and the alignment pin and mount an 8mm wide x ~300mm long led strip to it instead of the bar. I haven't tested this but I don't see why it wouldn't work.