When purchasing a light bulb for a fixture, it is important to keep a few things in mind.
Lamp base: When purchasing globes, it is important to check the type of lamp base your fitting requires. This information can be found labelled on the lamp holder or on the rating label of the product which can be found on the bracket or canopy of the fixture. Common lamp bases are: Edison Screw (ES): E27 or E14, Bayonet: B22 or B15, GU10 or G9 etc...
Wattage: All fixtures with bulbs have a max rated wattage that would be labelled inside or on the lamp holder. The max rated wattage refers to the max recommendation that should always be adhered to and not exceeded, to prevent over-heating and damage to the light fixture. E.g if a fixture has a max rating of 60W, there are equivalent wattages that are recommended to safely maintain the same level of light, e.g Incandescent 60W and it's equivalents = Halogen 42W, CFL 14W and LED 9W, can all be safely used as the ratings are all below 60W.
Shape & finish: It is also important to consider the globe shape and finish when selecting a bulb. It is important to consider the finish of the globe, for example if the fixture is transparent and the globe is visible, a decorative vintage look globe may be selected as opposed to a standard LED globe as the transparent fixture will show off the globe. Lastly, it is also important to consider the shape of the globe and whether the shape of that globe would fit into the fitting. For example, for very narrow or small fittings you may want to select a long tubular globe instead or a classic globe that may be too wide for the fitting.
*Important: When replacing a bulb, the fixture should always be switched off before attempting to change the bulb.