The Lumen level or the brightness level in a room differs from a person to person. Some like dim level of light in living room and brighter in family room, kitchen or office. Brighter levels are always required and welcomed in the areas of work like kitchen. Calculating the amount of light you want in a particular area is not a difficult task once you have a clear requirement in your mind.
To start with, calculate the area of the room in sq feet.
For example we consider a room of 15 feet x 20 feet. The area of this room is 300 sq feet.
Lighting experts recommend 40 to 60 Lumen per sq feet for a moderate lighting in a room.
We opt for 50 Lumen per feet.
Multiply the room area by the Lumens desired by you.
Total desired Lumen in our room is (300×50) 15000 Lm.
Select the lights (CFL, LED, Bulbs) you want to put up in the room and check the rating in Lumen for each one.
If your select MORIC A2528 12W LED fixture, it gives out roughly 1200 Lm. So you may have to put 13-14 such fixtures to properly lit up the room to your desired level.
This is just an approximate calculation. There are many other factors to consider like the colour of walls, floor and furniture which help to reflect the light back and make room look brighter. Height of the roof and position of the mounted lights are also major factors to be considered while planning the lighting for any room.
Side note: To convert Lux to Lumen, multiply Lux by 10.76