Headlamp bulb wattage

[David.H]

What sort of Wattage was used on short chassis cars? I had wondered if the "dim" or dip function was a "blow out the offside candle" variety, but all the wiring diagrams I have seen show twin filaments being fed. Would a stop/tail (18/6) be up to it as a "stopgap"?

[AustinWood]

I believe the headlight bulbs were 18W.
My 1929 car has side lights and head light, the latter being single filament and no main beam.
When headlights are on the front sidelights, which are in the headlight reflector, go out. Taillights stay on.
Years ago, after a Cambridge Austin Seven Club meeting, a gathering in the car park did a test on headlights.
There were cars present with a variety of power headlights; 18W, 24W, 36W and a dizzy 48W.
These were observed in turn and I think 36W came out best. Less than that was dim because of low power, 48W was dim because the system couldn't cope with the power.
18W headlights on a Ruby I had caused me inadvertently to drive into a field because I couldn't see the sharp right hand bend.

[Mike Costigan]

I don't think any short-chassis cars were fitted with twin filament bulbs, except possibly if the very late cars had the Lucas-Graves lamps. I believe the early cars with scuttle-mounted lamps had an arrangement in the switch panel to change the wiring from series to parallel, which meant that, on dipped beam, you couldn't see the radiator cap 

[AustinWood]

The R47 headlights on my 1929 car have 2-contact, single filament headlight bulbs. This means it would be easy to fit twin filament bulbs and a separate earth.
However I am content with the LED bulbs I now have. No more driving into fields!

[Rick F]

If you do not intend to drive in the dark, I guess you could stick anything in to give the correct "vintage appearance" - although I do believe that the law says if lights are fitted they must work.

However, if you are driving at night it makes sense to have the brightest lights you can, for your own safety and that of other road users.

This is one area where I feel authenticity may definitely defer to safety and best practice.