One Bulb Two work (2 in 1) 1- Normal Lighting bulb when there is power. 2-Emergency Lighting bulb when there is power cut. Lithium battery with full capacity 4-hour backup. After 4 hours battery will still work with dim light up to 10 hours. Charging time is 8-10 hours. Once Battery is fully charged it auto cuts the power and protects battery from getting overcharged. Automatically turns on AC to DC while power cut. When power is off the Identification Circuit of this inverter bulb automatically switches on DC emergency light. It can be switched off is not needed. Full electronic control, Low power consumption & high efficiency. It works as normal Light Bulb when power is on, and as an Inverter Bulb when power is off from grid. Emergency Lighting bulb when power is off.