Nigel M presented the following explanation :
Sorry, I should have said. This is a stable, so enough to see the horse!
I was thinking of around 40W of tungsten, so I think an 8W fluorescent
tube would be ideal.

But where to get one to run from 12V, what size battery, how to
re-charge, and what sort of cable and switching?

Any caravan or outdoors type of dealer would have the complete tube and
fitting for £10 to £15. They would also probably stock the type of
battery you need, a type intended for deep discharge rather than a car
type battery.

www.maplins.co.uk stock a range of solar cells. One of the smaller ones
intended to charge a 12v battery would easily cope with replenishing
8watts used for one hour.

Simply wire in twin flex (the smallest size of mains flex is adequete)
from the battery positive (+ve) via an in line fuse of 5amps to both
the + of the solar cell and one terminal of a switch. From the second
terminal of the switch to the + of the light. The negative (-ve) of the
battery needs to be connected to the -ve of the solar cell and the -ve
of the light.

Black = -ve, it is conventional to use the blue in the flex for this.
Red = +ve and it is convention to use the brown in the flex for this.

Almost any switch can be used, but probably a pull cord switch as used
in a bathroom might be best. Any DIY store would stock these, as would
the electrical wholesalers.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org