After some dry lighting tests , I found that there is not enough light in the armrests, except just above the LED, where it is too strong. So I enlarged the openings for the LED, and painted flat white inside the armrests.

Diffusion is much better, more uniform (even if it is not as apparent in the photo, due to the camera sensibility). To save space, the LEDs are arranged laterally instead of perpendicularly, and a white box is then built around (again for diffusion, but also to prevent light leakages) These LED must have the lip sanded on one side so that it fits properly in the white box.

The LED behind the dashboard is permanently installed. It is set in a cap (a button from an old calculator or toy) .