Lumen is the international unit of measurement for light. Defined as the amount of light falling on a surface of one square foot, every point of which is one foot away from a candlepower source. Lumens per Watt (LPW) is the measure of the efficiency of a light source, equal to the lumens produced, divided by the power (watts).
What does that mean to you? All incandescent light bulbs are tested by the manufacturer and are assigned a “lumens per watt” measurement. This measurement can be a bit more difficult to determine with low voltage bulbs such as MR16. The lamp manufacturer will give you the maximum candle power and you have to do a calculation to determine the lumens.
Be sure to buy light bulbs that will give you the highest lumens (most light output) for the watts burned. Luckily the Federal Trade Commission (FTC) is making the job of comparing light bulbs easier. In 2011 the FTC started requiring manufactures to use the new Lumen per Watt label on boxes. Look for the new label and choose the highest lumen light bulb available for your application.