The beam angle of a lamp is the angle at which light is emitted. As a reference a standard halogen GU10 bulb will use a beam angle of some 38 degrees. Within limits it doesn’t make much difference if the beam angles are slightly different – for example you would be unlikely to notice the difference bewtween 35 and 38 degrees. However, a bulb with a beam angle of 80 degrees will spread the light over a larger area and so the amount of light that falls in a particular space will fall.
If you choose a bulb with a narrow beam angle (say 20 degrees) then you will get noticable “spotting” on the floor. Narrow beam angles are often used for highlighting particular objects, such as within display cases, and also where light distribution needs to be restricted.
For most domestic applications a beam angle in the 30 – 45 degree range will be fine given a ceiling height of around 2.4m
Example of a 30