Bob Rimm kindly shared this ip:

“Thank for the news letter! As an electronics engineer I have been using Led’s since they first came on to the market. Some additional tricks is take two LED’s, add a 1N4148 diode in series with each on and wire them so that the anodes of Led and Diode go in one direction and the second set goes in the opposite direction. This will give you a brighter light and if you use a pulsing source such as the output of a 555 timer, you can adjust the frequency. This will allow one to increases or decreases the light output. Usually a frequency of approximately 1 Kilohertz will give you a usable amount of light.”