Microwaves are very efficient because they heat the food much more than the (highly reflective) walls of the oven. However, they heat the food throughout and thus won't make a nice crisp.
Most metals are also near perfect reflectors in the thermal infrared as well. Infrared light heats and crisps food much like hot air and can be generated with an incandescent filament at nearly 100% efficiency.
Would an infrared oven, using reflective walls, be an efficient replacement of a conventional or toaster oven? A microwave is high power but cooks for a very short time. This oven would take as long as a toaster oven to cook but hopefully would use much less power because most of the energy ends up in the food.
