IAN LANG ELECTRONICS
Figure 2: a GU10 connector. It consists of 2 pins which twist and lock into a base (shown below). The width between the centre of the pins is 10 mm, hence GU10. In North America since 2009 the GU24 connector (exactly the same but with 24mm between the pins) is becoming common, replacing the old E27 standard.
Figure 1: top, Edison Screw fitting, common in Europe and ubiquitous in North America, bottom Bayonet fitting, the most popular kind for mains lighting in the UK. Right, table of sizes for the caps.
Figure 3: G9 fitting.
An odd one this, used on halogen bulbs and one you don't often see. Mainly they are on lamps but you can buy adaptors to allow them to run from a Bayonet or Edison fitting on your ceiling lights.
Used where a small, 40 or 60W incandescent bulb would have been.
Figure 4: MR fitting.
Used in lamps and uplighters, the base cant really be up-hanging.
Figure 5: one of my all-time favourites just for its simplicity is the P9 miniature flange, aka Krypton Bulb or torch bulb. These are bright for their size, and run on a variety of voltages up to 7.5V, but the big drawback is their life expectancy of only about 20 hours. This is the price of brightness. If you've got a torch or lantern with a P9 in always make sure you've got a spare; some torches used to have a compartment for this very reason.
Here's a table of some more. I'm not sure who created it, but it was issued by ledbulbs.co.uk :
This is an American one issued by replacementlightbulbs.com
It hasn't come out too clearly, sorry about that.
Ian Lang April 2013