Great Western Coffee Shop

Does anyone know the theory behind the design of the sort of fairly recent railway signalling that has the appearance, close-to, of a cluster of lights of various brightnesses?

Mark

Do you mean the LED serachlight type, that shows all 3 colours in one apperture?

Apologies, I should have taken a photo before asking that question. This might be one, but the camera may have evened out the light output from the individual elements as the one I'm thinking of doesn't look quite like that to the eye.

http://www.scot-rail.co.uk/photo/scaled/15214/ (http://www.scot-rail.co.uk/photo/scaled/15214/)

Mark

Sounds to me like an LED signal in which a large number of small LEDs are so arranged so as  to give a similar appearance to an incandescent lamp behind a fresnel lens.
Viewed from a short distance or photographed with a long lens, the individual LEDs can be seen.

As well as standard clear, danger, and caution signals other types are used including repeater signals for situations when sighting of the main signal is poor.
The old type used a pivoted black arm in front of an illuminated white background. The arm was horizontal for stop and at 45 degree angle for caution OR clear.
The led version produces a similar effect but with the refinement that the backlight can be green for clear and yellow for caution.
The older type had to be enclosed behind glass to exclude dirt, birds and insects, the moving parts needed lubrication and the lamps needed replacement. The LED type is maintenance free.

Yes, modern LED signals are compact and lightweight - especially that particular design (VMS I think?).  They’re designed to be seen clearly, with no phantom aspects, at all distances, but especially at the ‘sweet spot’ around where the AWS magnet is.