The idea of Iron Man's infinite power Arc Reactor is awe-inspiring and led me to create the next best thing..a solar Arc Reactor night light!
Step 1: How it works
The solar cell charges a lithium ion battery during the day and at night the LED Arc Reactor style ring switches on.
The circuit uses a photo transistor especially tweaked using a 75k resistor to turn on the night light when it starts becoming dusk.
The transistor in the circuit simply activates as the on switch when the light levels change.
Step 2: The parts list
x10 white smt LEDs (XPCWHT-L1-0000-00C01)
Tin copper wire, any strong flexible gage.
Blank pcb breadboard.
x2 3.6v Lithium ion battery (100mah+) (6v IN SERIES)
x2 3v 50ma Powerfilm solar cells (6v IN SERIES)
The pictures show 1 battery and 1 solar cell, my photo transistor is power hungry so I've since added an extra battery and solar cell in series to create 6v through the circuit.
You can use an LDR and just 3v but the circuit changes ever so slightly.
Step 3: The circuit
Follow my (bad) circuit drawing and picture of the PCB.
The schottky diode is on the back of my PCB between the positive of the solar cell and battery positive.
Create a ring of tin copper wire and a slighlty smaller one to fit inside and solder ends together.
Solder the negatives of all LEDs to one ring and positives to the other ring.
It can be tricky and the rings get very HOT!
The photo transistor I'm using is a bit power hungry so I've doubled up x2 3.6v batteries and x2 3v solar cells creating 6v for both. See my Micro Dark Switch Instructable circuit for exact parts to follow my PCB.
Ignore the small black resistor between the emitter of the photo transistor and cathode of the LED on my PCB, it's just a 0hm resistor where I cut the board by mistake!