Ultraviolet quickly than violet light itself. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted shortly thereafter, and it remained popular throughout the 19th century, although there were those who held that these were an entirely different sort of radiation from light (notably John William Draper, who named them "tithonic rays"). The terms chemical rays and heat rays were eventually dropped in favor of ultraviolet and infrared radiation, respectively. In 1878 the sterilizing effect of
Photovoltaic effect electric energy. The photovoltaic effect can also occur when two photons are absorbed simultaneously in a process called two-photon photovoltaic effect... The photovoltaic effect was first observed by French physicist A. E. Becquerel in 1839. He explained his discovery in "Comptes rendus de l'Académie des sciences", "the production of an electric current when two plates of platinum or gold immersed in an acid, neutral, or alkaline solution are exposed in an uneven way to solar radiation." Besides the direct excitation of free electrons, a photovoltaic effect can also arise simply due to the heating caused by absorption of the light.