How much light do you need to light a room?  There had been a simple formula for it:  Room length x room width x 1.5 = required wattage.

The problem is people no longer talk about watts; they talk about lumens.  The reason is that there is no agreed upon standards for determining equivalent wattage for CFL or LED light bulbs which are being used more frequently than ever., So 60 watts from one bulb might not provide the same light as a 60-watt bulb from another manufacturer.  Thus the switch to lumens.

What are lumens?  Lumens are the actual amount of ambient light coming from a lamp.  The basic calculation for lumens is 20 lumens per square foot.  This, of course can vary based on a number of factors.  For example, you will need more light if you have dark walls and/or furniture.  You might also want extra light by kitchen appliances, etc.  Here are some general guidelines for how many lumens you need.

Living Room
Ambient lighting for a living room should be 1,500-3,000 lumens. Task lighting for reading should be a minimum of 400 lumens.

Kitchen
Ambient kitchen lighting should be 5,000-10,000 lumens, with task lighting at counters, sink and range a minimum of 450 lumens in each area.

Bathrooms
Ambient lighting in a bathroom should be 4,000-8,000 lumens, with task lighting at the mirror a minimum of 1,700 lumens.

Dining Room
Ambient and task lighting combined in a dining room should be 3,000-6,000 lumens.

Bedrooms
Ambient lighting in the bedroom should be 2,000-4,000 lumens, with a minimum of 500 lumens for each reading light, and 400 lumens for closet lighting.

Hallways and Entry
Ambient lighting for entries and stairways should be 1,200-4,000 lumens; ambient lighting for a hallway should be 1,200-2,500 lumens.