Ender 3 LED bar (+source inventor)

Print flat on the big surface. then rotate 90 degrees and mount on the back of the X-axes on the Ender 3.
There is room for the LED strip on the bottom, and a bit of strain relief on the side, combine the cable run to the Extruder cable run.

For mounting, you need 2 bolts and v-screw nuts that go into the 2 holes.

For LED I would suggest 24V white less since the Ender 3 has 24V. else you need a step-down converter. Those less mostly have a + (plus/24V/high) and a - (min/ground) connection. just follow some connection tutorial for them specific online.