By putting different chemicals inside, the tubes could be made to produce a variety of colors, and elaborate Geissler tubes were sold for entertainment. More important, however, was its contribution to scientific research. One of the first scientists to experiment with a Geissler tube was Julius Plücker, who systematically described in 1858 the luminescent effects that occurred in a Geissler tube. He also made the important observation that the glow in the tube shifted position when in proximity to an electromagnetic field. Alexandre Edmond Becquerel observed in 1859 that certain substances gave off light when they were placed in a Geissler tube.
Fluorescent lamps require a ballast to stabilize the current through the lamp, and to provide the initial striking voltage required to start the arc discharge. Electromagnetic ballasts can produce an audible humming or buzzing noise. In North America, magnetic ballasts are usually filled with a tar-like potting compound to reduce emitted noise.
The development of the neon light also was significant for the last key element of the fluorescent lamp, its fluorescent coating. In 1926 Jacques Risler received a French patent for the application of fluorescent coatings to neon light tubes. The main use of these lamps, which can be considered the first commercially successful fluorescents, was for advertising, not general illumination. This, however, was not the first use of fluorescent coatings; Becquerel had earlier used the idea and Edison used calcium tungstate for his unsuccessful lamp. Other efforts had been mounted, but all were plagued by low efficiency and various technical problems. Of particular importance was the invention in 1927 of a low-voltage “metal vapor lamp” by Friedrich Meyer, Hans-Joachim Spanner, and Edmund Germer, who were employees of a German firm in Berlin.
The wavelengths that humans are typically able to visualize lie in a very narrow range between approximately 400 and 700 nanometers. Humans can observe and respond to stimuli created by what does xd mean in roblox visible light because the eyes contain specialized nerve endings that are sensitive to this range of frequencies. However, the remainder of the electromagnetic spectrum is invisible.
In addition to general lighting, special fluorescent lights are often used in stage lighting for film and video production. They are cooler than traditional halogen light sources, and use high-frequency ballasts to prevent video flickering and high color-rendition index lamps to approximate daylight color temperatures. Many countries are encouraging the phase-out of incandescent light bulbs and substitution of incandescent lamps with fluorescent lamps or LED and other types of energy-efficient lamps.
The wavelength of electromagnetic radiation visible to the human eye is called visible light or simply light. Wavelengths of the range of between 380 to 740 nanometers are perceivable to human eyes. Considering the frequency, this corresponds to a band frequency between 405 to 790 THz.