Outdoor Lighting Glossary

Come across a lighting word you aren't sure of? Completely new to the world of lighting? We feel your pain! Here you will find a collection of terms and concepts that should help to make your life easier.

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Select the first letter of the word from the list above to jump to appropriate section of the glossary.

Scotopic Vision - Sight involving the eye's rods, which respond to low levels of lighting, below .034 candela per square meter, or .01 footlamberts.

Shielding - An arrangement of light-controlling material to prevent direct view of the light source.

Shielding Angle (of a luminaire) - The angle from the horizontal at which a light source first becomes visible. It is the complementary angle of the cutoff angle. In the case of a luminaire shielded by a reflector or parabolic cell louver, it is important to ascertain also the shielding angle to the reflected image of the light source, as this is often almost as bright as the source itself.

SON - Another term for a high pressure sodium (HPS) lamp

SOX - Another term for a low pressure sodium (LPS) lamp.

Spacing Criterion - The maximum recommended distance that interior fixtures should be spaced to ensure uniform illumination on the workplane. The height of the luminaire above the workplane multiplied by the spacing criterion equals the recommended maximum center-to-center luminaire spacing.

Spacing Ratio (SR) - The ratio of the distance between luminaire centers to the height above the work plane. The maximum spacing ratio for a particular luminaire is determined from the candlepower distribution curve for that luminaire and, when multiplied by the mounting height above the work plane, gives the maximum spacing of luminaires at which even illumination will be provided.

Spectral Energy Distribution (SED) Curves - A plot of the level of energy at each wavelength of a light source.

Spectroradiometer - An instrument capable of separating and measuring light waves.

Specular - Mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word is used to describe the finish of the material used in some louvers and reflectors.

Sphere Illumination - The illumination on a task from a source providing equal luminance in all directions about that task, such as an illuminated sphere with the task located at the center.

Starter - A device used in conjunction with a ballast to start electric-discharge lamps, usually older fluorescents.

Step lens - A plano-convex lens similar to a fresnel lens but with the concentric rings cut into the plano side.

Stroboscopic Effect - Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources. Sometimes called "strobe effect."

Subtractive color - The removal of light of various wavelengths, by filtering or reflection, e.g. a magenta filter subtracts the green from the light path, whereas the pigment of yellow paint reflects the red and green components of the incident light but absorbs (subtracts) the blue. (See Additive Color Mixing.) (alt) The creation of colors by filtering out (subtracting) certain wavelengths from a typically white (multi-wavelength) light source. For example, putting a magenta filter in the path of a white light source subtracts green light. Typically, the filters used in a subtractive color mixing system are cyan, yellow and magenta; thus, this is usually referred to as the CYM color mixing model. This is the color mixing model used in Cyberlight.