Not a bad guess, Keith. At about 4-ins diameter these were light lenses and could have been used in a hand-held lantern, for example, and acting by focusing the light into a tighter beam - similar to lighthouse optics. But at about that size, in red, amber or green, they would have been for traffic or railway lights.
Headlight lenses have a different and more complex geometry, and were also made by Chance for Lucas headlight units.