Greenhouse lighting

[Green Aura]

I need some advice, folks.

We are turning what was my old therapy room into a greenhouse. It has long, deep SW facing windows and through the short summer will have light pretty much 24/7 but the nights then draw in quite quickly until it's dark after 3(ish) until about 10 or 11 next day.

The light fitting for the therapy room was very low and appropriate for the room's use then, but we'd like to be able to extend the growing season as far as possible.

Any ideas what to replace the lighting with?

[Green Aura]

I should mention we don't want visits from the police when they've been informed we're suddenly using vast quantities of electricity, or enormous bills.

[Odsox]

LED grow lights unless you have deep pockets.
There's plenty available on a well know auction site for just those people you hinted at.

For small scale growing you can get aquarium fluorescent tubes that are quite energy efficient.
Just make sure they are labelled "growlux" or similar.