These are LED motion sensor activated night lights. They're designed not to come on when the room/area is already lit.
I was in my local Robert Dyas and noticed the last two of these on the shelf at £9.99 - can't see them any cheaper online. There are two slightly different models, I'm linking to Amazon here just for information:
1.) Osram Nightlux TM Automatic Wireless LED Night Light White:
You can set them to come on for 10 seconds, 1 minute or permenantly on detection of motion.http://www.amazon.co.uk/Osram-Nightlux-Automatic-Wireless-Night/dp/B002BX173I/ref=sr_1_1?ie=UTF8&qid=1328457071&sr=8-1
2.) Osram Spylux TM Automatic LED Night time Motion sensor White:
You can set it to come on when motion is detected (for 12 seconds or longer if there is still motion), or set them to be permenantly on as a light.http://www.amazon.co.uk/Osram-Spylux-Automatic-Motion-sensor/dp/B001EYTJ44/ref=cm_cr_pr_product_top
(Only 78p more expensive at Amazon if you can't get to a Robert Dyas).
* Lights up dark corridors, steps, closets, basements and garages preventing accidents.
* Water and weather resistant, making it perfect for both inside and outside use.
* Easy to fit with the aid of a magnetic fitting or glue.
* Batteries included (3 x AAA)