On 4/26/2020, John Upton wrote:
"During my MGA 1600 rebuilding project a friend presented me with two (original) 5¾” Lucas SLR 576 spot lights (driving lights). .... Concerned about the load if I used either the original BPF tungsten 48w bulbs or halogen P36S bulbs (also 48w), I opted for two P36S LED positive earth bulbs (20w) from Better Car Lighting in the UK (£30 each). Each bulb has two LEDs either side of quite a thick divider (photos).

Unfortunately, installed in the SLR 576s, these bulbs produce not one but two beams of light each (photo – in which only the spotlights are working!). These twin beams diverge as distance from the car increases – so one beam lights up the road just in front of the car and the other illuminates branches on trees high above. To check that it wasn’t anything to do with the light units I installed a BFT tungsten bulb in one light – this gave a normal single beam. I suggest therefore that the type of LED bulb I used is best avoided.

Better Car Lighting have agreed to refund the cost. I have now installed two P36S halogen bulbs powered from a relay, basically all as described on page ET-205, with good results". -- John Upton

This is case of the LEDs not being positioned at the focal point of the parabolic reflector. Obviously the wrong LED for this application. It might be good for some other lamp where it only has to light up brightly inside of a refractor lens, but not shine in any particular direction, like a rear fog lamp perhaps. This must serve as a caution not to use this particular LED for a focused spot lamp.