1. Chapter 8
Quantity of Lighting
© 2006 Fairchild Publications, Inc.

2. Definition of terms
Rules of thumb
Precise calculations

3. Measurement terminology2 4 1 3 5

4. 1: Luminous intensity: light flow in a particular direction

8. 2: Luminous flux: total output

9. Lumen
The quantity of light falling on a one square foot area illuminated to one foot-candle

10. 3: Illuminance: density of light landing on a surface, in Lumens per square foot (“foot-candles”)

13. Adjusting the target numbers
Task proper: %
Immediate surroundings: %
Surroundings: %

14. 5: Luminous exitance: light reflected from (or passed through) a surface

15. Inverse square law

16. Illumination level over distance

17. Good for initial layout
Rules of thumb
Good for initial layout

18. Recessed downlighting

19. Recessed wall washers ¼ height of wall
space the same distance as they are from the wall
Always check mfr

21. Fluorescent downlight layout
Determine spacing you want – will depend on the grid you use and the fixture output

22. Spot lighting

25. Precise calculations Good for final layout
Use where levels are important
Point source for specific locations (paintings, sculptures, tasks)
Whole room calculations (more open areas)

26. Point calculation
Footcandles=candela/distance2

27. So, using this lamp from 10’ away gives you how many footcandles?

28. What about this fixture?

29. Use photometric data for exact luminaire and lamp

30. Watts per square foot method
Very rough
Does not take ceiling height into account

32. Project: this classroom
Lectures and computer use (20-50fc)
25’x45’=1125

33. True calculations Called the “Zonal Cavity” method
Use many, many factors
Room cavity ratios (RCR)
Coefficient of utilization for luminaires (CU)
Light loss factor (LLF)
Lamp lumen depreciation (LLD)
Luminaire dirt depreciation (LDD)
© 2006 Fairchild Publications, Inc.
Chapter 7
Quantity of Lighting

34. fc = Number of lamps  Initial lamp lumens  LLF  CU
Basic Formula
fc = Number of lamps  Initial lamp lumens  LLF  CU
Area
Inserted multiplication sign from Symbols
© 2006 Fairchild Publications, Inc.
Chapter 7
Quantity of Lighting

35. Recommended surface reflectances

36. Typical reflectances

37. Definition: the room cavity ratio

38. Using a form:

40. Luminaire Dirt Depreciation

41. Illumination gradients: what we’re looking for

42. Illumination gradients

43. Project: this classroom
Lectures and computer use
25’x45’
12’ ceilings
GWB
White walls

44. Use an online calculator
Zonal cavity method
Precise: based on exact luminiare

45. Let’s use this beauty from Philips/Lightolier

47. Enter project data and post result to GullNet
Light loss factor
Room dimensions
Target FC

48. Row 1: Do this room
Row 2: White gwb ceiling/dark wood furniture/dark painted wainscotting
Row 3: This room, with 18’ ceilings

49. In-class exercise Measure light level on different work surfaces
Use an app:
Light Tester for Android
LightMeter for iPhone

50. Another in-class exercise: Re-lamping my kitchen
Replace (2) 60A19 overhead luminaire lamps
Replace (6) 50PAR20 halogen downlight lamps

52. Process
Find LED with equivalent output (means you need to find original output)
Figure return on investment over life of LED (assume $0.37/bulb) – try this site

53. Who can save me the most? Try shopping for a cheaper lamp
Consider beam spread on PAR20s

54. Any questions about the midterm?

55. Let’s meet at 2 at the Home Depot in Danvers, in the lighting section
We will also go to craft store
We will be looking at materials for custom luminaires