MK IV 1940's - headlights

Does anyone have details or can point me to getting details of the headlights for the MK IV. It seems to me that there are two quite different types, distinguished by their outer diameter.
Any details would be appreicated.
TerryT

Welcome Terry.
The 1-1/2 Liter 4 cylinder cars had Lucas LBD166 or P80 headlights which are the smaller types.
The 2-1/2 Liter and 3-1/2 Liter 6 cylinder cars had Lucas P100 headlights which are the larger type.
There were slight variations for left and right side driving countries, and I believe for France yellow bulbs were required.
You also occasionally see the sealed beam conversions which were required in some parts of the USA at that time.