Iron Rod Farm, at one point, had about 100 laying hens. This meant that every day, 5-6 dozen eggs had to be collected, cleaned, and examined before being sold. Candling, which uses a bright light source on one side of the egg to see internal defects (such as a bloody white) or cracks in the shell, greatly enhances the quality control process. However, the current method (holding a flashlight under the egg), is really inconvenient for more than say a dozen eggs at a time.
There are actually professional egg candlers out there, but at the price of $70 for the type we would need, I was sure I could make one for less. The primary difficulty in using a flashlight is that you need to be in a dark room, so that you can see the egg clearly, but when you lift an egg off the flashlight, it tends to blind you. Most of the commercial models had a pushbutton switch to overcome this problem. I decided that a foot pedal would be more convenient, as you would then have both hands free to handle the eggs.
I ended up sourcing the LED through ledsupply.com, in a pre-made aluminium and plexiglass housing. This provided both a heatsink and an easily cleanable surface. I then fit the driver and a potentiometer into an aluminium housing, soldered up all the connections, and insulated the connections. The power supply and foot pedal were sourced online very inexpensively. The total cost came to around $40.
The LED turned out to be more than sufficiently bright, wich led to the added benefit of being able to use the candler in a lit room. The potentiometer allows adjustment of the intensity for when it is used in a dark room, or if an egg is particulary thick-shelled. The initial design called for a flexible rubber fitting to be attached to the housing, to provide a good seal for the light, and a soft surface for the eggs, but it turns out a paper towel secured with a rubber band works just as well.