A carbon arc therapeutic lamp from the early twentieth century is pictured above. When its carbon rods are touched together and removed with a short gap left between them, a dazzling light, almost as brilliant as the sun, blazes forth with an abundance of infra-red, visible, and ultra-violet rays that have great therapeutic value—just like the Sun’s rays.
Priests and physicians realized the healing qualities of ultra-violet rays in antiquity. The practice of heliotherapy was carried on throughout the Greco-Roman era. Herodotus, Cicero, Vitruvius, Pliny the Elder, and Galen were among the ancient writers who wrote about it. After the fall of the Roman Empire, the practice apparently fell into oblivion, but its use was noted by a Persian writer in the early Middle Ages and the practice was apparently carried on to the present time.
In the nineteenth century solar-ray therapy was practiced by artificial means—when carbon arc lamps were reinvented. The type of carbon arc health lamp illustrated above, and much larger versions, were then used to cure a variety of ailments such as tuberculosis, psoriasis, and unnatural hair loss. Modern studies show that ultra-violet light has many more beneficial effects—in lowering blood pressure, increasing heart efficiency, reducing cholesterol, and assisting in weight loss, to name a few. It is also an effective treatment for many other health issues.
Above, we see a vintage sample of the type of carbons used with the Healthmaster and protective eyewear commonly used to prevent any burning of the eyes by the emission of its unseen ultra-violet rays. Staring at its brilliant blaze without protective goggles will make one feel like there is sand in the eyes. The ailment is commonly called "Welder's Eye." It is quite uncomfortable, but not life-threatening, and eventually clears up.
Here we see the Healthmaster connected up to a power meter. Pushing down on the black plunger on top of the lamp will release the two top carbons, and they momentarily drop down to touch the lower two to strike the arcs as they spring back up and establish the gaps to allow the arc light's combustion.
Above we see some of the electrical guts behind the light. When the arc is struck, alternating current will surge through the springs above and their resistance and inductive reactance will limit the current available at the carbon tips. The Healthmaster's carbon rods are wired in series so both sets of carbons must touch simultaneously to initiate the arcs.
The meter above is indicating the actual voltage and power being consumed by this arc light. On the left we are reading about 1100 watts and the meter on the right shows about 110 volts. Ohm's law tells us that it must be drawing about 10 amperes, which is within its acceptable electrical rating, indicated on its nameplate above, 110 to 120 volts and 12 amperes.
Here we see the arc light blazing away again. Note the light mist rising above the healthmaster, toward the right. It contains vaporized carbon, a real fine, white powdery dust of which a little sometimes settles and can be detected inside its aluminum reflector, if one inspects it carefully. The white powder blended in well with the white walls of ancient Egyptian tombs. This may well be why archaeologists have not yet realized that arc lights were used to illuminate the dark tomb walls so the artisans could effectively paint detailed histories upon them. Smoky torches, and dim, dirty oil lights as well as feeble candles would have left a lot of noticeable residue—not found in newly-opened tombs.
Ancient electric lighting in antiquity is covered in depth in The Electric Mirror on the Pharos Lighthouse and Other Ancient Lighting.