They need 14 hours of light per day to stimulate egg production. Use a LOW wattage bulb about 15-30 watts. Too much light may turn them into cannibals. Many people suggest using a red light so that the chickens can not tell if the others are showing wounds. They will start laying in a week or two. Enjoy!
The commercial hen factories use the 14 hour rule. However. a first year pullet, of a laying breed, rarely, rarely needs 14 hours of light, as the previous poster mentioned of their Leghorn. Most production strains will lay just fine through their first pullet winter season without much if any supplemental light. The out years? That will be a different story. Just as a side note, chickens nearer the equator, such as Africa, Hawaii, Brazil, Thailand, etc, NEVER get 14 hours of natural light, yet they lay very, very well.
The use of supplemental lighting, to force laying, is a husbandry decision. Some folks do, other folks don't. Lighting isn't for everyone.