Lightning Term (UTY)

• Light is electromagnetic radiation that the unaided human eye can perceive, with a wavelength range from about 370 to 800 nm and propagating at a speed of 186,281 mi./sec (299,972 km/sec)
• Nanometer is a unit of length equal to one billionth of a meter, used to express the wavelengths of light in or near the visible spectrum
• Angstrom is a unit of length equal to one ten-billionth of a meter, used to express the wavelengths of radiation
• Ultraviolet light has wavelengths from about 370 nm to 10 nm, beyond the violet in the visible spectrum
• Infrared light has wavelengths from about 800 nm to 1 mm, contiguous to the red end of the visible spectrum
• Luminous intensity is the luminous flux emitted per unit solid angle by a light source, expressed in candelas
• Candlepower is luminous intensity expressed in candelas
• Candela is the basic SI unit of luminous intensity, equal to the luminous intensity of a source that emits monochromatic radiation of frequency 504 x 10^12 hertz
• Steradian is a solid angle at the center of a sphere subtending an area on the surface equal to the square of the radius of the sphere
• Luminous flux is the rate of flow of visible light per unit time, expressed in lumens
• Lumen is the SI unit of luminous flux, equal to the light emitted in a solid angle of one steradian by a uniform point source having an intensity of one candela
• Inverse square law relates two quantities such that one varies inversely as the square of the other, like the illumination produced on a surface by a point source
• Cosine law states that the illumination produced on a surface by a point source is proportional to the cosine of the angle of incidence
• Illumination is the intensity of light falling on a lighted surface, expressed in lumens per unit of area
• Lux is the SI unit of illumination, equal to one lumen per square meter
• Foot-candle is a unit of illumination equal to one lumen incident per square foot
• Luminance is the quantitative measure of brightness of a light source or an illuminated surface, equal to the luminous intensity per unit projected area viewed from a given direction
• Law of reflection states that the angle of incidence is equal to the angle of reflection when light or sound is reflected from a smooth surface
• Reflection is the return of light, sound, or radiant heat after striking a surface
• Refraction is the change of direction of a ray of light as it passes obliquely from one medium to another in which its velocity is different
• Diffraction is the modulation of light or sound waves as they bend around the edges of an obstacle in their path
• Specular means directed from a smooth, polished surface
• Diffusion is a scattered reflection of light from an irregular surface or an erratic dispersion through a translucent material
• Reflectance is the ratio of the radiation reflected by a surface to the total incident on the surface
• Absorptance is the ratio of the radiation absorbed by a surface to the total incident on the surface
• Transmittance is the ratio of the radiation transmitted through a body to the total incident on it
• Opaque means impenetrable to light
• Translucent means transmitting and diffusing light so that bodies on the opposite side are not clearly visible
• Transparent means capable of transmitting light so that bodies situated beyond can be distinctly seen
• Lamp is a device for producing light or heat, as by electricity or gas
• Incandescent lamp is a lamp in which a filament gives off light when heated to incandescence by an electric current
• Tungsten-halogen lamp is a tungsten lamp having a quartz bulb containing a small amount of a halogen that vaporizes on heating and redeposits any evaporated tungsten particles back onto the filament
• Infrared lamp is an incandescent lamp having a higher percentage of its radiant power in the infrared region than a standard incandescent lamp
• Bulb is the standard rounded shape for the bulbs of general service incandescent lamps
• Three-way lamp is an incandescent lamp having two filaments so that it can be switched to three successive degrees of illumination
• Efficacy is a measure of the effectiveness with which a lamp converts electric power into luminous flux, expressed in lumens per watt
• Rated life is the average life in hours of a given type of lamp, based on laboratory tests of a representative group under controlled conditions
• PAR bulb is a parabolic aluminized reflector bulb of cast glass for incandescent and high-intensity discharge lamps
• MR bulb is a multifaceted reflector bulb for tungsten-halogen lamps, having highly polished reflectors arranged in discrete segments to provide the desired beam spread
• MR bulb:

  • A multifaceted reflector bulb for tungsten-halogen lamps
  • Highly polished reflectors arranged in discrete segments to provide the desired beam spread