The Energy Labeling Rule requires light bulb manufacturers to give consumers key information in an easy-to-read format.
The Lighting Facts label gives shoppers the information they need to buy the most energy-efficient bulb to meet their lighting needs. The label includes a bulb’s brightness, energy cost, life, light appearance, and wattage. In addition, the principal display panel on the front of packaging focuses on lumens, a measure of brightness, rather than on watts, a measure of the amount of energy used, and includes the estimated yearly energy cost for each bulb. Bulbs themselves also feature lumens, and in the case of CFLs, a mercury disclosure.
For more info, please refer to FTC site.