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This is a set of 36 long hood LNER style 3-aspect Westinghouse searchlight signal heads with provision for a PLCC4 LED. A suitable LED is available from Rapid Electronics part number 56-3000.
This signal type is still in use today and is typical of the type used widely over the former LNER network.
As well as the opening in the back to take a PLCC4 LED there is a 2.5mm diameter socket in the bottom to fit the head on to the top of a tube.