This simple White LED lamp switches on when its surroundings turn dark. It is an ideal portable lamp in picnic sites. It uses solar energy for charging the battery and an LDR for automatic switching.
6 Volt 100 mA solar panel is used to charge the battery during day light. During day time, the lamp never turns on due to the action of LDR. When the LDR conducts in day light, transistor T1 turns on and the base of T2 will be grounded. This keeps T2 off and the LED will not light. When there is darkness, LDR cease to conduct and T1 turns off. T2 then forward biases to light the White LED. LED turns off if LDR again gets light. Adjust VR1 to set the sensitivity of LDR at the particular light level.
Use 6 volt rechargeable battery and High bright White LED. S1 can be a small push switch with lock. It can be used to switch off the lamp when not in use. The PCB in the image was designed to add 4 LEDs to get high bright light with 12 volt battery.
Filed Under: Electronic Projects