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”.