Lightbulbs - Such a small, basic thing, yet so many choices! In this guide I'll attept to demystify the various types of lightbulb to help you choose.
Most of us don't give too much thought to lightbulbs. One stops working and we just go to the cupboard (or shop) and get another one. That is until one doesn't do the job for us we want it to - it simply doesn't fit, or it somehow just doesn't provide the 'right' sort of light!
For most of us, it would take quite an extreme circumstance for us to deem the lighting provided by a light bulb as 'wrong'. It would need to be so dim we couldn't actually see what we needed to see or so bright we started to feel a bit headachy.
The Danish, however, might be an exception to this - we Danes seem to have much more of a sense of the quality of artificial illumination, probably because they've been brought up to appreciate 'the right lighting, in the right location'.
I'll tackle the location element of this in more detail later. For now let's focus on the main different types of lightbulb you're likely to encounter.
Lamp Fitting Types - Edison or Bayonet

In Europe there are two main lamp fittings - E14 and E27. The letter E stands for Edison, meaning it will be a screw fitting. The number is the length of the fitting in mm.
The bulb pictured (left) is a E27 in a UK standard shape and size.
Additionally, since the late 1800s the UK has had an alternative to Edison, the Bayonet fitting. These have two main fittings - The B15 and B22, with the number also representing the length in mm. Although their use is declining in line with standardised Europe-wide production, Bayonets continue to be used.
A key feature of Bayonet fittings is that they are still made with in-built switches, whereas modern Edison fittings very rarely have them, meaning you need a switch on the cable for table lamps. The lamp on the right is a c1970s British 'Shattaline' style lamp with its original B22 fitting with in-built switch.
Where the switch is located is a matter of personal preference, but there's no denying that the traditionally styled metal B22 firttings, that are still made in the UK, can add a great deal of charm to lighting.
Below are two B22 lightbulbs plus two vintage lamps with new, vintage style B22 metal fittings with in-built switches. The lightbulbs are a pink incandescent in the UK standard shape, and a G95 LED with a 'radio spiral' design' - the same bulb shown in the blue candlestick lamp in the main photo.

For both Edison and Bayonet lightbulbs, the larger of the two sizes is the main one used in most standard lighting, with the smaller one used in specialist lighting, especially small lamps or lamps that have multiple bulbs like chandeliers.
Both Edisons and Bayonets are completely safe to use and provide the same quality of illumination. Edison bulbs perhaps sit a little more steadily in their fittings but, unless you go wobbling your bulb, that's not really an issue.
Lampshade Considerations

The only real consideration is that if you have a vintage British lampshade it will probably only fit on a B22 fitting.
If you buy a modern lampshade in the UK it will probably have an easily removeable adapter ring inserted in it enabling it to be used with either B22 or E27 fittings.
READ NEXT: Part 2 of this definitive guide to choosing household lightbulbs.