Emergency lamps do not have a facility to prevent the deep discharge of battery if the lamp remains on during day time. The fluorescent lamp filament also damages if it is glowing in low battery voltage. This causes blackening of the filament side that indicates the damaged filament. So we have to switch off the lamp in the morning and switch it on again in the evening. By adding this circuit in the emergency lamp, you can reduce the job of daily switching. This circuit offers two advantages
1. It prevents unnecessary discharge of battery during daytime
2. It charges the battery only during night. This save energy and prevents overcharging of the battery.