A-Lights are described in detail in my A-Lights page. They were defined in the 1943, 1965 and 1988 Rule Books.

Extract from Regulation 2 of the 1965 Automatic Signalling Regulations:

Station Switched in and "A" Light NOT illuminated - When the "A" light is not illuminated the signal is in all respects a Stop and Stay signal.

Station Switched Out and "A" Light ILLUMINATED - When the "A" light is illuminated the signal is converted into a Stop and Proceed signal and the regulations applicable to Stop and Proceed signals become applicable to it.

"A" lights are also provided on Intermediate Stop and Stay signals protecting points and crossover roads at double-line switch-locked sidings.

The "L" (Loop) light is used on Arrival Signals in Single Line Automatic (SLA) areas. More recently it has been used on Arrival signals in Track Warrant territory. It is defined in the 1943, 1965 and 1988 Rule Books.

Extract from Regulation 2 of the 1965 Automatic Signalling Regulations:

When the "L" light is illuminated it indicates that the points are set for the crossing loop and that the points off the loop are in the normal position but not necessarily that the loop is unobstructed.

Extract from 1965 Automatic signalling Regulation 20

Stop and Proceed signals at the entrance to attended and unattended crossing stations are called Arrival signals, and are fitted with a short-range light which shows a white letter "L" when the points are set for the loop and all points off the loop are in the normal position.

For the use of L and A lights on Arrival signals in Track Warrant Territory see my A-Lights page.

Introduced in the 1943 Rule Book but was not in the 1965 Rule Book. According to Semaphore To CTC   there is no known installation of a Grade Signal.

1943 Automatic Signalling Regulation 3 (b) stated (in part):

The signal is displayed by a special yellow-light letter "G" placed below the marker light on a Stop and Proceed signal, and is provided to obviate the necessity for goods trains stopping on an Up gradient when the section is occupied. (See Regulation 6 (d).)

Regulation 6 (d) stated:

Where a Low-speed Grade signal is provided, the Enginedriver of a goods train may pass the Stop and Proceed signal at "Stop" without stopping, and proceed at a speed not exceeding six miles per hour to the next fixed signal, being prepared to find the section obstructed by a train, or by one of the conditions in clause (a) hereof.

1965 Automatic Signalling Regulation 2 (a) stated (in part):

Low Speed - Points are in the proper position but track may be occupied or suitable for low speed only. Proceed at Low speed prepared to find track occupied, and ready to stop clear of any obstruction.

See my Low Speed Light page for more detail.

1965 Automatic Signalling Regulation 1 (c) stated (in part):

At places where a reduction to medium speed is not required, or where it is not necessary to indicate that a train is approaching a signal which may require a reduction to medium speed, signals having one Multi-aspect or Searchlight unit are provided. These signals are equipped with a Marker light as the second and lower light.

Regulation 3 (a) stated (in part):

The lower Multi-aspect or Searchlight in the case of double-unit signals, and the Marker lights in the case of single unit signals, are so placed that by their position in relation to the upper lights they serve to distinguish Stop and Proceed signals from Stop and Stay or Departure signals. In the case of a Marker light the position of the lamp itself provides this indication.

See my Markers page for more detail.