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Luminaire lightdistribution basics
Presented by Morgan Catha,Grandlite Product Development Engineer
September 26, 2014
Photometry concepts
Lumen: A quantity of emitted light energy in the visible spectrum (“luminous flux”). Defined in terms of the sensitivity of the human eye to light. One lumen is 1/683 watts or more of visible light energy, depending on the spectrum of the light source.
Candela: A measure of “luminous intensity”, defined as lumens per solid angle (measured in steradians). Expresses how much light is being emitted in a particular direction.
Photometry concepts
Footcandle: A measure of “illuminance”, the amount of visible light energy falling on a surface. Defined as one lumen per square foot. Another common unit is “lux”, equal to one lumen per square meter.
Photometry concepts
Luminance: An expression of the intensity of light leaving a surface in a particular direction. Measured in candelas per square meter.
Photometry concepts
“Brightness”
“Brightness”
‘"Brightness" should be used only for nonquantitative references to physiological sensations and perceptions of light.’
-- Federal Standard 1037C, the Federal Glossary of Telecommunication
Terms (1996)
Photometric Testing
Rotating mirror Goniophotometer -- measures light output
Grandlite goniophotometry
laboratory
Photometric Testing
A type C rotating mirror goniophotometer is used to record candela values for each angle
Photometric Testing
The candela values are stored in a .ies file
Photometric Testing
Photometric Reports
Polar candela plot • Shows cross-sections of light intensity
• Useful for seeing the overall shape of a luminaire’s light distribution
Photometric Reports
Isoilluminance plot • Shows lines of equal illuminance on target surface
• Useful for seeing how a luminaire illuminates the area around it
Photometric Reports
Luminaire Classification System Graph • Shows backlight, uplight and glare by sector
• Useful for seeing how the BUG rating is determined
B.U.G. Rating
B.U.G. Rating
B.U.G. Rating
B.U.G. Rating
B.U.G. Rating
IES Cutoff Classifications
IES Cutoff Classifications
IES Cutoff Classifications
IES Cutoff Classifications
IES Roadway Types
IES Roadway Types• Type I - Half-maximum candela trace falls between 1 MH LRL on the House side and 1 MH LRL on the Street side • Type II - Half-maximum candela trace on the Street side is beyond the 1 MH LRL but not beyond the 1.75 MH LRL • Type III - Half-maximum candela trace on the Street side is beyond the 1.75 MH LRL but not beyond the 2.75 MH LRL • Type IV - Half-maximum candela trace on the Street side is beyond the 2.75 MH LRL • Type V - Has circular symmetry being essentially the same at all lateral angles around the luminaire • Type VS - Zonal lumens (below 90-degress vertical) for each of the eight horizontal octants (0-45, 45-90, 90-135, 135,180, 180-225, 225-270, 270-315, 315-360) are within +-10% of the average zonal lumens of all octants
IES Roadway Types• Very Short (VS): The maximum intensity points to a point in the VS zone of the grid, 0-1.0 MH TRL
• Short (S): The maximum intensity points to a point in the S zone of the grid, 1.0 - 2.25 MH TRL
• Medium (M): The maximum intensity points to a point in the M zone of the grid, 2.25 - 3.75 MH TRL
• Long (L): The maximum intensity points to a point in the L zone of the grid, 3.75 - 6.0 MH TRL
• Very Long (VL): The maximum intensity points to a point in the VL zone of the grid, > 6.0 MH TRL
IES Roadway Types
IES Roadway Types• Maximum candela point furthest lateral point between 2.25 and 3.75 mounting heights = Medium
• Half maximum candela trace furthest longitudinal point between 1.75 and 2.75 mounting heights = Type 3
IES Flood Types
IES Flood Types
BeamField
10% of maximum candela
50% of maximum candela
Maximum candela
IES Flood Types
Example: NEMA 7x7 means the field angle is 130 degrees or wider in both the horizontal and vertical planes. For short, “NEMA 7”.