|Is there a device that would provide a variable output of radiated energy in the infrared that would be obtainable to experiment with? — NAT, Marion, SC
You can produce a broad range of infrared lights with a heat lamp. A heat lamp looks very dim because most of the thermal radiation it emits is in the infrared portion of the electromagnetic spectrum. Just attach the heat lamp to a normal light dimmer and you'll be able to vary its infrared output over a wide range of intensities. Its frequency range will also shift farther away from the visible as you lower its temperature by turning down the dimmer. If it produces more visible light than you want, you can put a filter in front of it that absorbs visible light while permitting infrared light to pass. Such filters are certainly available from filter companies such as Hoya or Corning but cheaper versions (perhaps even plastic filters) may be found through scientific supply companies.