You may have noticed that now there is a Lumen value listed on the side of bulb boxes. Lumens are a measurement of how much light a bulb gives out in all directions.
Lumens = Light Output
The higher the lumens rating means the brighter the bulb will appear.
How many lumens do you require?
This depends on a number of factors like room size and height of your ceiling, type of fitting and bulb, also what you are using the room for.