This is my light bulb heated, very inexpensive black garlic oven. I use a Huskee Tough Guy EPS cooler lined with aluminum foil (reflective side inward-facing, secured with Elmer's Glue-All), with tiles lining the bottom to give the jars a surface on which to sit, as well as to protect the foil. I use jars filled with stones and water as thermal batteries, with the water and stone as thermal mass, and the stones and glass as IR absorbing materials, that should radiate the heat evenly. I am able to do 24 jars of garlic at the moment, putting twelve on each end of the cooler. The whole unit is powered by a light bulb appropriate to the cooler size and ambient temperature.
A full step-by-step guide to what I did to make my oven is present on my blog, located at http://omniafaciat.blogspot.com/2012/12/the-black-garlic-oven-post.html
. Also included in the post is a download link for the research on light bulb strength that was done before I started the project.