SmartCharge LED [$35] energy efficient light bulbs supply 4 hours of battery backup during power outages. SmartCharge LED bulbs stay on when the power goes out thanks to the built-in rechargeable battery. The built-in rechargeable battery in each SmartCharge LED Bulb recharges itself during normal use, requiring no additional maintenance. It works like a normal light bulb, and fits a standard fixture, but continues to work during power outages. Energy efficient instant on light bulbs by SmartCharge are only 5.5 watts, but replace a standard 40 watt incandescent bulb.