#71

In late 1799, Frederick Hershell started experimenting with light that he passed through different prisms.

He performed an experiment in 1800 where he measured the temperature of the different colors that passed through a large prism he created.

He found that purple was the coolest and red was the hottest temperature of the spectrum of colors. He tested the dark area, just beyond the red and was amazed to find the hottest part of the spectrum was in the area with no color. He found that there was something there, even though he could not see it.

Soon after, in 1801, Johann Ritter was experimenting with silver chloride, which turned black when exposed to light. He studied Herschel’s experiments and decided to run his own tests on the different colors of light in the spectrum.

Johann made test strips of paper coated with silver chloride and timed how long each took to turn black. Just beyond the violet end of the spectrum he found the most intense reaction occurred where no color was visible. (Ultraviolet light - ultra means ‘beyond’ + violet).

(Johann’s work would later lead to the creation of the photograph)

In 1877, two scientists in England (Downes & Blunt) discovered that sunlight kills bacteria. Sugar water in test tubes on a shady windowsill turned cloudy, while similar sugar water in tubes in the sunlight remained clear. Bacteria was growing in the shaded tubes and the ones in direct sunlight stopped the bacteria from growing…

.

In 1892, Marshall Ward performed tests with anthrax and typhoid demonstrating that the bacteria killing actions seen in Downes and Blunt’s tests were from the ultraviolet part of the spectrum. The Ultraviolet (UV) light killed the bacteria, and that its effectiveness depended upon the amount and length of exposure to UV light.

Niels Finsen was awarded the Nobel Prize for Medicine in 1903, for his work using Ultraviolet (UV) light to fight tuberculosis.

Bill Nagengast, Lighting Engineer

Solas Ray Lighting, Retired