what is the unit of wavelength of light
wave packet
title: Light text: Light Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10 to 7.00 × 10 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz). The main source of light on Earth is the Sun. Sunlight provides the title: Wavelength text: light—in free space, the phase speed is the speed of light, about 3×10 m/s. Thus the wavelength of a 100 MHz electromagnetic (radio) wave is about: 3×10 m/s divided by 10 Hz = 3 metres. The wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm (for other examples, see electromagnetic spectrum). For sound waves in air, the speed of sound is 343 m/s (at room temperature and atmospheric pressure). The wavelengths of sound frequencies audible to the human ear (20 Hz–20 kHz) are thus between approximately 17 m and 17 mm, respectively. Note title: Visible spectrum text: Visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 700 nanometers. In terms of frequency, this corresponds to a band in the vicinity of 430–770 THz. The spectrum does not contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations like magenta, for example, are absent because they can only be made from a title: Luminous intensity text: The luminous intensity for monochromatic light of a particular wavelength λ is given by where If more than one wavelength is present (as is usually the case), one must sum or integrate over the spectrum of wavelengths present to get the luminous intensity: Luminous intensity In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit. Photometry deals title: Optical radiation text: Optical radiation Optical radiation is part of the electromagnetic spectrum. It is subdivided into ultraviolet radiation (UV), the spectrum of light visible for man (VIS) and infrared radiation (IR). It ranges between wavelengths of 100 nm to 1 mm. Electromagnetic waves in this range obey the laws of optics--they can be focused and refracted with lenses, for example. Optical radiation may be produced by artificial sources, such as UV lights, common lightbulbs, and radiant heaters, but the primary source of exposure for most people is the sun. This exposure can result in negative health effects. All wavelengths across this range