You could put the Arduino in deep sleep, if you wanted to and that LED will still blink. With a little work, you could probably adapt this idea to any number of circuits out of the 555 playbook ...

How about a quick review. Here's how you make a UV light with a smart phone. Start with a smart phone that has an LED light (for the camera flash). You want two things from this light.

To regulate the brightness level of an LED with PWM, just connect it to one of the PWM channels (with a 1K resistor in series) and use the “analogWrite” command to control the duty cycle, as shown in ...