|GWR & BR(WR) Signals:
The notable features of the Great Western lower quadrant signal was the tapering pitch-pine post, the 'wasp-neck' spectacle, and the elaborate pointed finial (designed to protect the post from water ingress) painted to match the colour of the signal arm. The arm was also of wood. some four feet long. During the 1930's wood begain to be replaced by steel for both arms and posts.
There was quite a variety of signal arm shapes in earlier GWR days but the range was eventually simplified.
Ground signals - for shunting - went through a more complex development but finally became standardised as white discs with a red band.
Red arms have a white stripe and yellow ones a black chevron - this simple addition makes the colour stand out against the background environment.
The arm has three positions: ON WRONG OFF.
ON is the most restrictive indication (a red arm in the ON position means stop here). ON is defined as between 0 and 5 degrees in the lower left-hand quadrant (of an imaginary circle with its centre being the pivot of the arm).
OFF means proceed and is between 45 and 60 degrees.
WRONG is a failure to properly indicate either ON or OFF.
At night an oil lamp gave light filtered through a tinted spectacle. The green spectacle is larger to accomodate the wider latitude of degree. The 'green' spectacle is actually blue-green, which with the yellow of the oil lamp gives a strong green light. The red spectacle is a deep ruby red to resist the appearance of a light tending towards orange. Yellow is relatively recent (since 1923).