I found an old street lamp in the trash. For another project ( a colored mobile ), I had bought a bunch of rgb addressable leds (the WS2811 kind). The association of both things with an arduino, a lithium battery and a little bit of electronics, I built this color lamp.
The lamp is driven by an arduino (precisely a cheap clone coming from China) with the Neopixel library from Adafruit. There are 6 WS2811 LEDs (Adafruit's Neopixels), a push button to change mode and a multi turn potentiometer which controls the color of the lamp or its rotation. All this works on battery : two 18650 cells coming from a dead laptop battery. The batteries are charged by USB using a dedicated circuit : the bq24090 from TI (who gives free samples away !)
The RGB leds need a voltage of at least 4.5 V whereas the nominal voltage of the lithium battery is only 3.7 V. It was necessary to add a small boost converter to produce the needed 5 V supply when the thing is battery powered. The voltage regulation is handled by the arduino.