Johnny OneSpanner wrote:

Thanks for all the comments.
For wiring reasons, there will probably be only one light, so a 70W Sodium
lamp looks like a good solution.

Another option might be a 70 watt HQI metal halide[*] lamp. Much better
colour rendering than SON and pretty good lumens/watt efficiency,
although not quite as good as sodium. Googling "hqi floodlight
photocell" finds a few suitable luminaires.

[*] Don't confuse "metal halide" with "tungsten halogen" - they're
totally different things.

--
Andy