A summary of the schemes used in the lighting industry to classify luminaire light distributions

1. Luminaire light
distribution basics
Presented by Morgan Catha,
Grandlite Product Development Engineer
September 26, 2014

2. 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.

3. 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

4. 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

5. Luminance: An expression of the intensity of light leaving a surface in a
particular direction. Measured in candelas per square meter.
Photometry concepts

6. “Brightness”

7. “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)

8. Photometric Testing
Rotating mirror Goniophotometer
-- measures light output

9. Grandlite
goniophotometry
laboratory
Photometric Testing

10. A type C rotating mirror goniophotometer is used to
record candela values for each angle
Photometric Testing

11. The candela values are stored in a .ies file
Photometric Testing

12. Photometric Reports
Polar candela plot
• Shows cross-sections of
light intensity
• Useful for seeing the
overall shape of a
luminaire’s light distribution

13. Photometric Reports
Isoilluminance plot
• Shows lines of equal
illuminance on target surface
• Useful for seeing how a
luminaire illuminates the
area around it

14. Photometric Reports
Luminaire Classification
System Graph
• Shows backlight, uplight and
glare by sector
• Useful for seeing how the
BUG rating is determined

15. B.U.G. Rating

16. B.U.G. Rating

17. B.U.G. Rating

18. B.U.G. Rating

19. B.U.G. Rating

20. IES Cutoff Classifications

21. IES Cutoff Classifications

22. IES Cutoff Classifications

23. IES Cutoff Classifications

24. IES Roadway Types

25. 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

26. 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

27. IES Roadway Types

28. 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

29. IES Flood Types

30. IES Flood Types
BeamField
10% of
maximum
candela
50% of
maximum
candela
Maximum candela

31. 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”.