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Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily. The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approximately 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light.
A basic distinction is between isotropic materials, which exhibit the same properties regardless of the direction of the light, and anisotropic ones, which exhibit different properties when light passes through them in different directions. The optical properties of matter can lead to a variety of interesting optical phenomena.
A Morse code light is light in which appearances of light of two clearly different durations (dots and dashes) are grouped to represent a character or characters in the Morse Code. For example, "Mo(A)" is a light in which in each period light is shown for a short period (dot) followed by a long period (dash), the Morse Code for "A".
By definition, visible light is the part of the EM spectrum the human eye is the most sensitive to. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. This action allows the chemical mechanisms that underlie human vision and plant photosynthesis.
The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the band gap of the semiconductor. [5] White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device. [6]
Since that refractive index varies with wavelength, it follows that the angle that the light is refracted by will also vary with wavelength, causing an angular separation of the colors known as angular dispersion. For visible light, refraction indices n of most transparent materials (e.g., air, glasses) decrease with increasing wavelength λ:
The source of Einstein's proposal that light was composed of particles (or could act as particles in some circumstances) was an experimental anomaly not explained by the wave theory: the photoelectric effect, in which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage.
This power is not a measure of the amount of light output, but rather indicates how much energy the bulb will use. Because incandescent bulbs sold for "general service" all have fairly similar characteristics (same spectral power distribution), power consumption provides a rough guide to the light output of incandescent bulbs.