Paragraph 3 of this has some info. Neon pits were unsuccessful in assisting aircraft to land.
Just had a look at the ATB plan and I note there is no number for the Neon Beacon Pit. On the landing field, just to the east of hangar 97 there is a small circle with a 'X', which according to the key denotes 'building in course of erection'. I suspect this may be it, which would put it around here The site plan is 1933, corrected to 1939.
From my notes:
... which doesn't explain the 'pit'. Hmm will investigate further.Neon Beacon (pre WWII)
The GEC manufactured unit consisted of a square section vertical steel framework sited at least twenty feet above the ground. It contained four neon tubes, each 20 feet in length and 30 mm in diameter. The red light output was around 1,400 candles. Power consumption per tube was 300 mA, from three separate 2.25 kVA transformers. A 'morse flasher' was incorporated, and the unit was switched from the control tower.