ex-Great Western (UK) Colour Light Signals

[Saxham_Market]

Whilst browsing Flickr for some photos of "modern" colour light signals, I happened upon this picture which picqued my curiousity. It was taken at Bristol Temple Meads in the 1960s:

http://www.flickr.com/photos/rgadsdon/7195245662/sizes/l/in/photostream/

The two smaller, lower level, heads look as though they each have a pair of white lamps, so I'm guessing that these are subsidiary / shunting / calling on heads and that both lights would come on to permit movements beyond the main head on that side. Can anyone confirm that this is the case (and that it's not, for example, some form of route indication)?

Thanks in advance.

 

[itareus]

They are most likely "calling on" signals but I think you will need an expert to give you a definitive answer - perhaps asking on one of the UK signalling forums will provide the result.