Here is a simple Solar Night lamp that turns on automatically at sunset and stays on till morning. It uses 1 Watt High Bright White LEDs to illuminate a confined area.
6 Volt 150 mA Solar panel is used to charge the battery during day time. This mini solar panel cost around Rs.300. Its positive and negative terminals can be directly connected to the battery. Current from the Solar panel passes through IN 4007 diode which acts as polarity protector as well as rectifier. 470 uFcapacitor functions as a reservoir to give steady charge to the battery in varying sunlight conditions.
Lamp circuit is an automatic switch controlled by an LDR. During day time LDR conducts taking the base voltage of the Driver transistor SL 100 and it will be non conducting to keep the LEDs off. At sunset, resistance of LDR increases and transistor conducts. White LEDs get power and switches on.
Day time – Lamp Off
Night – Lamp On
Use any Medium power NPN transistor like BD139, TIP 122 etc if SL 100 (CL 100, BEL 100) is not available. Placing the LEDs in front of a reflector ( or Mirror) will increase the light.Light from the LED should not fall on the LDR.Use 6 volt rechargeable battery. Adjust the POT to set the sensitivity of LDR so that at the required light level, LEDs turn on.Alternately, 4.5 volt battery or mobile battery can be used.Backup time depends on the capacity of the battery since the White LED takes 3 volts and 100-300 mA current.
Solar Panel Setup
Front view of Solar panel- LED can be used to test its working
LED is glowing when the Solar panel is in sunlight
Back side of Solar panel with diode, capacitor and Test LED
Solar panel connected to battery
This can be used to charge Mobile phone
Final charger setup