Glossary Of Terms

The SGIA Glossary of Terms serves as an excellent industry terminology resource. It is the language by which we all communicate, without it universal understanding would be impossible. Language and our ideas about how it is interpreted change rapidly. SGIA is aware of this and continues its effort to keep our constituents well informed about changes to the increasingly complex industry terminology. The definitions are for general reference only. Usage may vary between companies, individuals, or national and country customs. The information presented is as accurate as the authors and editors can ascertain and SGIA assumes no responsibility for the use of information presented herein.


  • Light bug
    A round light sensing device with a cord attached for connecting to a radiometer for measuring UV light intensity.
  • Light emitting diode (LED)
    A semiconductor device that emits incoherent light.
  • Light emitting diode display
    Type of electronic changeable copy sign that uses hundreds of light emitting diodes in single and tri-color matrices.
  • Light integrator
    An instrument used when exposing photo sensitive materials that measures the intensity and duration of a light source.
  • Light intensity
    Brightness of a light source, equal to the function of the power of the source over a designated distance.
  • Light meter (exposure meter)
    A device for measuring the light reflected from a subject, or in some cases, also measuring the intensity of light falling on the subject.
  • Light reflectance value
    The amount of light reflected by a given color. (Yellow has a higher light reflectance value than purple).
  • Light sensing units
    A device capable of converting the energy of any light striking its surface to electrical or mechanical energy.
  • Light source
    Aside from the sun, any device capable of converting electrical, mechanical, or chemical energy into a light-emitting form.
  • Light stability
    A measure of the ability of a pigment, dye, or other surface material to retain original color and physical properties, with extended exposure to sunlight or other light sources.
  • Light struck
    Photosensitive materials accidentally exposed to light because of incorrect handling methods or because of light leaks in the camera or darkroom.
  • Light table
    A table with built-in lights under a ground glass (or similar) top used for spotting negatives, opaquing positives, tracing, examining, making overlays, and cutting of stencil film.
  • Light trap
    A passage into or out of a photographic darkroom, usually composed of overlapping portions or revolving shields that do not permit the passage of light rays from the outside.
  • Lightfast (sunlight resistance)
    The capability of a material, coating, or ink to resist fading when exposed to sunlight or artificial lighting.
  • Lightness
    Equals value of color; perception by which objects are distinguished from gray objects and light from dark objects.
  • Light-source geometry
    The effective increasing of undercutting angle that occurs as the light source gets closer to the copy.
  • Lightweight
    A class of fabric made of 26 or 28 single yarn.
  • Lightweight paper
    Book grade paper of basis weight 40# or less with high opacity.
  • Lim
    Acceptable abbreviation for limit.
  • Lime crown glass
    An optical crown glass containing substantial quantities of calcium oxide.
  • Lime glass
    Glass containing substantial quantities of lime, unusually associated with soda and silica.
  • Limit switch
    Electromechanical device used to control travel distance.
  • Limited coordinates specification
    A specification or standard issued to cover the need for requirements unique to one particular department, primarily found in military documents.
  • Line art
    Single color diagram or drawing usually black and white with no intermediate grayscale.
  • Line copy
    Any type, design, drawing that can be reproduced without using a halftone screen.