LED light bulbs have taken over as the greenest choice when it comes to lighting your home. They are long-lasting, mercury-free, energy efficient and cast a soft, white light. But when shopping for LED bulbs, it can be tough to determine which one is right for your house. To figure it out, look for the lumens rating on the package. This is a measurement to determine the output of light from the bulb. Figure out what old-fashioned incandescent bulbs worked in what fixtures, and multiply the wattage of that bulb by 10. So, a 40-watt bulb times 10 would be a 400-lumen LED bulb.