There are several options when choosing lighting for emergencies. First, there are candles and light sticks. The standard votive candle burns for about 15-23 hours. I recommend the ReadyCandle. It burns odorless and smokeless liquid paraffin and lights large areas well. If you have children and don't want them to wander around with a flame, a would be an ideal collection to your and emergency supplies.
Some other good options are the many kinds of power sources that are out there. They have crank-powered, battery/rechargeable, AC/Adapter, solar, and shake lights. Crank-powered lights are ideal, because, for about a minute of cranking, you get 12 hours of power. Many of these emergency lights come with other features such as radios, cell phone chargers, USB outlets, sirens, and some are even waterproof!
Last, there are lanterns, which are great for lighting large areas. The lantern runs on kerosene and allows you to control how bright you want the light. The Krypton Lantern is battery powered, uses a krypton bulb, and is good for 8,000 hours of light!
These are all great sources of light for an emergency situation, and for everyday use. Which source of light is best for you? I hope this helps you decide. Be sure to take into account the different emergencies and factors, such as children, water, and other things.