- Ultraviolet light was first discovered in 1801 by German physicist Johann Wilhelm Ritter when he observed that invisible light rays, slightly beyond the violet end of the visible spectrum, darken paper soaked in silver chloride faster than violet light.
Source: safaltaHe called them "(de)oxidation rays" to emphasize their chemical reactivity and to distinguish them from the "thermal rays" discovered at the other end of the visible spectrum last year.
- Although the term was soon adopted and remained popular throughout the 19th century, some said that this radiation was quite different from light (notably John William Draper called it the "Tithonic Ray"). The terms "chemical radiation" and "thermal radiation" were eventually dropped in favor of ultraviolet and infrared rays, respectively.
- In 1878, the bactericidal effect of shortwave light was discovered by killing bacteria.