The idea was to have two LEDs, one is flashing all the time and the other one joins in as long as a switch is pressed. The LEDs then flash alternating. The hardware is very straight forward.
http://members.home.nl/b.vandam/lonely/pagina3.html
Built with high intensity 8000 to 11000 mCD white LEDs, these lamps sit directly on top of a 12 volt 2.7 amp-hour SLA battery and works well on a dining room or makes a great reading light with an adjustable head angle.
http://www.electronicpeasant.com/projects/ledlamps/ledlamps.html
This flashlight has three different modes of operation, regular flashlight, flashing LEDs, and sound-operated light.
http://www.electronicpeasant.com/projects/ledlamps/ledflash.html
Putting a small light switch on the LEDs lets me turn the lights off so I can sleep and keep the fans running for my hard drives.
http://www.elephantstaircase.com/wiki/index.php?title=LEDFanSwitch
This is a minimal parts lamp made with four white LEDs. It features regulated light output from 10V to around 20V and works well as a flashlight. Operating Current is 40ma
http://www.solorb.com/elect/solarcirc/4ledlit/index.html
It runs 8 white LEDs at 25mA of current with only 70mA of supply current at 12V. A high frequency switching regulator us used to reduce the power loss associated with multiple current dropping resistors.
http://www.solorb.com/elect/solarcirc/dc2dc8led/index.html
This circuit uses a set of 13 differently colored LEDs to generate a full color spectrum.
http://www.solorb.com/elect/misc/ledrbow1/
This circuit makes a nice lamp that consumes little power, runs cool, and has an incredibly long lifetime. The lamp puts out a warm yellow shade of light, the color may be adjusted by changing the number of red or green LED strings.
http://www.solorb.com/elect/solarcirc/ledlamp/index.html