Interesting footage of the M4 near
Heathrow (1977-1979) - is anyone able to identify the lanterns?
I have to admit I do like the current interest, in trying to identify lanterns from vintage film. Sometimes the subject in the frame is quite straightforward to identify, whilst on others the quality of the film (and filming) can make it more tricky.
Anyway, in this case it is quite difficult especially when trying to gauge the height of the twin arm columns. I suspect they are 12m (40'), however the lanterns dimensions suggest they are SLI (200W?) . The bowl is too deep to be a "less gear" Alpha 6 meaning only two other contenders. One possible thought might be GEC's Z9517 but its streamlined design would make it easy to identify - even on 35mm cine. Based on these assumptions, I think the lanterns on the central res' are Alpha 5s. Depending on the age of the installation, they may be the original Atlas version or the later AEI / BLI Amberline which would have been more numerous in the 70s.
The slip road lanterns on the second portion of the footage, look like Atlas Alpha 10s, based on their mounting height and canopy outline.
Then again...