Domestic wiring question - outside lights

We've 3 outside lights on our house, single switch operates all 3. They need replacing - this I can manage. However, is it possible to add a 4th light just by tying it into one of the existing lights? It would be approx 4 foot of cable, it's just around the corner of the house, or does it need to be wired right back into the lighting ring circuit?

The existing lights are floodlights, probably 150 or 250 watt halogens - the new lights are 24 watt low energy floodlights (R7 bulbs so equivalent to 140 watts) so will be using much less power than the existing lights.

Yes, that's fine- more so because of the drop down to ES lighting.

If cable is external use suitable external such as hituf or 3 core black rubber flex.

I would put some kind of control into the circuit - a timer or photocell. CFLs dont take kindly to being switched on and off frequently, especially so in cold weather. They come on very dim and take a good couple of minutes to reach full brightness in cold weather. So no good to just flick on while you pop out to the bin etc.

Thanks for the replies, the lights have PIR's fitted as well as being on a switched circuit - they'll only be activated occassionally when someone is round the back of the house. I've fitted one already and am impressed at the speed and white light of the R7's.