Question #2ac72

1 Answer
Jan 27, 2018

These are such a clever application of total internal reflection (T.I.R) - simply genius saving lives, costing very little.


In principle they are just a compact mass of prisms (reflective tape on Hi-Vis jackets is the same, just crystalline prisms bonded at random onto a fabric) that have a curious effect, irrespective of the angle of incident light i.e. it reflects light back towards its source irrespective of the angle of approach.

The principle is best described using a diagram to show the path of the rays:

The reference in grey below the diagram is an excellent website that gives a full explanation but I’ll just mention one aspect here - the condition required for total internal reflection, which is that the light must strike at an angle (to the normal) above the critical angle so it is important that the light is passing from (or attempting to pass) from a medium of high refractive index (optically dense if you like, with a high speed of light) into a medium with low refractive index.

This is achieved by choosing a backing material carefully (the low refractive index, high speed of light material.)