[TR] hi-beam questions.

[John Macartney]

Terry Smith wrote:
> The beam indicator light is to let you know the high beams areB on.
> Not sure why the call it "main," though.

Another British application of language usage.
Pre-1939, the majority of cars had different headlight functions than today. The left hand lamp had 
one filament that was 'dipped' using an electro-magnetic reflector in the lamp itself. Hence the 
name 'dip switch.' When operated, the dip switch dipped the LH beam and extinguished the RH 'main' 
beam - so the car was running only with one lamp on the LH side. The term 'high beam,' was only 
applied where the light emitted from the lamps was too high and illuminated trees and buildings 
rather than the road ahead.
Worth mentioning too, that the light 'spread' of these now ancient lamps was limited in the extreme. 
They were truly 'beams' rather than the blanket of light we know today.

Jonmac