Side-Emitting or Backlit: Lighting a Shallow Light Box

The problem with backlighting a shallow box

A backlit box works when the cone from each module has room to spread before it meets the face. In a 60 mm box with a thin diffuser, it does not: the array telegraphs through as a grid of bright patches. Adding modules makes the grid finer, not invisible, and it makes the box hotter.

What a side-emitting module does differently

A side emitter mounts on the inside wall of the box and fires across the cavity rather than at the face. The light reaches the face at a shallow angle and has travelled the width of the box before it does, so it arrives already spread. Nothing sits behind the face at all.

The asymmetric optic and why it has an orientation

The three side-emitting models here publish two beam figures, 65 x 10 degrees and 45 x 20 degrees, because the optic is asymmetric and the module can be mounted in either of two orientations. The wide axis should run along the face; installed rotated, the light hits the opposite wall instead of crossing the face.

Published depth bands for single and double-sided boxes

The side-emitting models publish 50 to 100 mm for a single-sided box and 60 to 200 mm for a double-sided one. The double-sided figure is larger because light crossing the cavity serves both faces on the way.

Choosing between the three models

The 4035V is the efficiency choice: 3 W, 360 lm per piece and 120 lm/W at 8 pieces per metre. The 7420V is the same 3 W at 300 lm and 100 lm/W but at a wider 7 per metre pitch. The 3828V drops to 1.5 W and 140 lm, for boxes where 3 W per piece would burn a bright band along the edge.