Effective Light Measurement and Data Use by Kevin Willmorth

1. Designers Light Forum
Effective Light Measurement and Data Use
Kevin Willmorth

2. Credit(s) earned on completion of
this course will be reported to AIA
CES for AIA members. Certificates of
Completion for both AIA members
and non-AIA members are available
upon request.
This course is registered with AIA CES
for continuing professional
education. As such, it does not
include content that may be deemed
or construed to be an approval or
endorsement by the AIA of any
material of construction or any
method or manner of
handling, using, distributing, or
dealing in any material or product.
___________________________________________
Questions related to specific materials, methods, and
services will be addressed at the conclusion of this
presentation.

3. Learning
Objectives
1. Determine what can be expected from light meters
2. Apply methods for increasing accuracy of
measurements
3. Determine uses of relevant data as a valuable tool
4. Set up an affordable small informal lab to evaluate
product in an office
5. Determine practices for tracking luminaire
performance over time (lumen depreciation and
other factors.
At the end of the this course, participants will be able to:

4. EFFECTIVE LIGHT
MEASUREMENT AND DATA USE

5. Lazy Metering
What’s wrong with your metering methodology?
You’re not using one!

6. Seeing vs. Perceiving
The human visual system has zero accuracy – cannot be
calibrated to a known standard
Variable, uncalibrated optical receiver
parts with adaptive features that change
with age and non-uniform perception 100
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0
Measured Light Percieved Light
Relative Perceived
Illuminance
RelativeActual
Illuminance

7. Visual Performance Response
• Human response to spectral color balance is not flat
• Varies by age, health, and individual preference
CCT S/P Ratio EVE Factor
Perceived
Illuminance
(20Fc Base @
3500K CCT)
2700K 0.8 1.56 12.82
3000K 1.25 1.09 18.35
3500K 1.4 1.00 20.00
4000K 1.6 0.90 22.22
5000K 2.0 0.75 26.67

8. Subjectivity
It’s too dark in here Wrong, too bright, I can still see you

9. Let there be Meters
• Changes observation from subjective (looks good) to
objective (numeric value)
• Allows comparisons and communication
– Between observers
– Over time
• Calibration = verifiable accuracy
Electrophot
1931
Weston 617
1932

10. Why Meter
• Evaluate a product
• Survey a lighting condition
• Verify performance against a product specification
• Verify performance against a calculated prediction
• Monitor performance over time (color)
• Track lumen depreciation
• Evaluate an environment to be lighted
– Solve problems or capture design data
• Understand more about light in a space
Testo 540

11. What We Measure
• Illuminance
• Color and color
characteristics
• Modulation (Flicker)
• A wide range of pecific
applicable
characteristics
– Brightness (luminance)
– X-y coordinate
– Duv shift
– Etc…

12. Data Extrapolation
• Color Accuracy
– CRI Ra and specific R values
– TM30 Rf and Rg
– McAdam Steps from standard center point
(product to product consistency)
• Visual performance
• Human factors
• Energy vs. Power
• Consistency comparison
• S/P ratio
• Horticultural
– PPFD (Photosynthetic Photon Flux Density)
– PAR (Photosynthetic Active Radiation)

13. Derivatives
• With accurate objective data comparisons can
be made and conclusions drawn between
parties
• Subjective variables can be considered within
the bounds of real data
• Perceptive variables can be factored
mathematically from objective uniform data

14. METERS AT WORK

15. Visual Response Factoring
• Meters are designed to match human visual response
– Without this, meters just measure total energy collected
at the photo receptor, whether or not it can be “seen”

16. Cosine Correction
• Cosine correction for illuminance measurements
• Does not provide luminance or spot measurement
Lambert’s cosine law

17. Accuracy vs Precision
• Accuracy is how close a meter will produce a
result against a known reference or standard
• Precision is how tight readings are to one
another, sometimes referred to as
repeatability

18. Accuracy vs Precision
Not acceptable in
professional measurement
applications
Acceptable for relative
measurements and
comparisons only
Ideal Result

19. LED and Analog Meters
Mismatch in technology delivers
very low accuracy and low
precision
If it doesn’t use a battery and has an analog gage- it is likely useless

20. Low Cost Digital Meters
Diffuser (Cosine Corrector)
Gage (Voltmeter w/firmware)
Photosensor (under diffuser)
Detachable sensor head is an excellent feature
Hundreds of acceptable meters at a wide range of price points
Generally offer high precision, but are widely
diverse in accuracy from product to product

21. Quality Digital Meters
Detachable sensor head
Array of multiple sensors
Offer durability and versatility – not necessarily any gain in precision
When calibrated properly, offer higher accuracy over low cost alternatives

22. Other Meters
Many older digital light Meters –
from fluorescent era forward
may still be usable.
Photographers light meters
-with spot attachment
Old color meters
are either
accurate or
precise enough
Verify against known meter
May not produce a linear response
High precision, variable accuracy
Low accuracy, high precision –
useful for relative comparisons
only – extrapolating Fc data is
impossible

23. Modern Meter Accuracy
Vs.
<$100
Illuminance
Only
>$2,000
Illuminance +
89 other
Parameters
Meters do not need to be expensive to be precise and accurate – requires verification
210
215
220
225
230
235
240
245
250
255
260
2700K 3000K 3500K 4000K 5000K
Illuminance
LED CCT
Meter Comparison
>$2000 <$100
All readings
within +/-
0.98%

24. Accuracy Comparison
Vs.
Analog meters disagree by >24% to one another = Poor Accuracy
A B C D E
Incand 36.6 36.1 36.4 29 22
Error Base 1.4% 0.5% 20.8% 39.9%
Assensetek LM-200LED Minolta T1H GE 214 GE 217
5000 LED 40.1 39.6 39.9 30 22
Error Base 1.2% 0.5% 25.2% 45.1%
Vs. Vs.Vs.
A B C D E

25. Color Meter Error
Vs. Vs.
Older photographic color meters
(C) lack accuracy (reference) and
precision (repeatability) when
reading LED light sources
-600
-500
-400
-300
-200
-100
0
2700 3000 3500 4000 5000
Color Deviation
A B C Low Light C High Light
A B C

26. LED - Meter Error
Vs. Vs.Vs.
2700K 3000K 3500K 4000K 5000K
DW58 10 22 32 45 60
LM-200LED 84 84 84 84 84
Minolta T-1H 83.7 84 85.1 84.1 84
GE 214 45.5 47 50 50 50
0
10
20
30
40
50
60
70
80
90
Illuminance
A B C D
A
B
C
D
Meter “D” lacks accuracy, but
has good precision
Meter “A” lacks both
accuracy and precision

27. App Base Meters
Diffuser (Cosine Corrector)
Software driven readout – iOS or
Android application
Multiple spectral sensor
Calibration using software
Generally offer good accuracy (if calibrated) and
acceptable precision

28. Remote Sensor Advantages
• Reduce operator
interference
• Allow meter to be
read with sensor
at any
angle/orientation
• Less physical
interference
between target
surface and sensor

29. Integrated Meters
Fixed sensor head can be an issue in task measurements
High end products, calibrated annually, offer high accuracy and precision

30. Delivered Data
CCT
CRI(Ra)(R1-R8)
Re(R1-15)
R1~R15
CQS
Illuminance
Foot Candle
CIE 1931
CIE 1976
Spectrum Diagram
C78.377-2008
IEC-SDCM
TM-30-15(Rf, Rg & Diagram)
Peak Wavelength (λp)
Dominant Wavelength (λD)
Purity
Duv
SP Ratio
PPFD (380~780 nm)
Flicker Frequency(5-200 Hz)
Flicker Percentage
Flicker Index
Temperature
Relative Humidity
90+ Parameters

31. Lab Meters – PC Connected
Properly set up lab instruments, calibrated regularly, deliver the
highest accuracy and precision due to elimination of external
interference from observers and field conditions

32. Software Interface
CCT
CRI(Ra)(R1-R8)
Re(R1-15)
R1~R15
CQS
Illuminance
Foot Candle
CIE 1931
CIE 1976
Spectrum Diagram
C78.377-2008
IEC-SDCM
TM-30-15(Rf, Rg & Diagram)
Peak Wavelength (λp)
Dominant Wavelength (λD)
Purity
Duv
SP Ratio
PPFD (380~780 nm)
Flicker Frequency(5-200 Hz)
Flicker Percentage
Flicker Index
Temperature
Relative Humidity
Desktop software evaluation tools

33. USING METERS

34. Core Principles
• Accuracy is attained by using meters of a
known quality related to a reference
– Use same meter for side-by-side comparisons
– Use calibrated meters to eliminate conflicts with
results between different testers
• Precision is attained by employing routines
and care in measuring that eliminate variables
– Distance variables and precision
– Control of light noise from surrounding sources
– Record keeping

35. Photometric Field Verification
• Meters reading Fc or Lux can be used to
generate candela data for comparisons
and evaluation
Distance “D”
(25’ or 7.62M)
Candela = Fc x D² (in feet)
Lux = Fc x D² (in meters)
Knowing the exact distance “D” is critical
Meter must be
aligned normal to
incident angle
12Fc x 25² = 7,500cd
129.17Lux x 7.62² = 7,500cd
12Fc
129.17Lux
55°

36. Transmission
Transmission =
FC or Lux through material / FC or Lux no material
Care must be taken to avoid stray light entering sensor
Align and fix meter
normal to incident
angle and set
distance
Fc through material = 112Fc
Fc without material = 238Fc
112/238 = 47% Transmission
Align material normal to
incident angle and close to
meter sensor – be wary of
reflective losses

37. Reflectance
Reflectivity =
FC or Lux off material (A) / FC or Lux direct (B)
Align and fix meter
normal to incident
angleFc off material = 112Fc
Fc direct = 238Fc
112/238 = 47% Reflectance
Distance A+C and B+C must
be identical
A
B
C
Incident and reflected
angles should match

38. Simple Benchtop Goniometer
Mount for small fixtures/lamps
Rotate in X axis in any degree
steps desired with controller
or manual crank
Mount any illuminance meter
here
Can be also be done with two tripods, protractor and string – just make the measured
distances and alignment as accurate as possible

39. Intensity and Scale
Benchtop Goniometer on steroids – the brighter and larger the source is, the
larger the distances involved

40. Relative Measurement
• Comparisons and ratios do not require absolute values
– Precision (repeatability) more important than accuracy
– Distance to subject and optics must be equivelant
• Comparison of a known reference source to another
A:
Known good
source
Ref: 600lm
Reads 36Fc
24” 24”
Reads 30Fc
600/30 = 20
(Ratio of lumens per Fc measured)
B:
Comparison
source
Lumens???
20 x 36 = 720lm
(Source B relative lumens)

41. Relative Measurement
Test Lumens Reading Multiplier
Referance 322 157 2.051
Reading Multiplier Lumens
Test 1 141 2.051 289.19
Test 2 172 2.051 352.77
Metric values are less important than
ratios to reference source
Requires a precise
light meter, but not
necessarily accurate
Ref and Test sources
must be of similar
optical character

42. Relative Spot Measurement
A
B
C
D
E
F
G
ID Ev Comp Ratio
A 10.1 A:C 1.4:1
B 5.7 A:B 1.9:1
C 7.2 E:C 1.7:1
D 8.1 A:D 1.2:1
E 11.9 E:A 1.2:1
F 9.1 A:F 1.1:1
G 8.0 A:G 1.3:1
Accuracy is less important than ratios between target surfaces measured with high
precision
Brightness ratio using a spot
meter

43. Common Measurement Errors
• Incorrect assumptions about what meter capability
– Assumptions of accuracy
– Misapplication causing poor precision
• Lack of care in setting up meter to capture measurement
– Inconsistent measurement location
– Inconsistent distance from source
– Lack of preparation for repeating measurements
• Interference from surrounding sources or reflective surfaces
• Mismatch between meter and light source
• Observer interference
– White shirt effect on illuminance
– Red shirt effect on color measurement
• Wrong meter setting
• Poor equipment condition and lack of calibration

44. Field Measurement
• Make a map of the space and note of conditions
• Establish a fixed x,y,z point that can be recaptured
later
• Use a meter sensor mount vs. hand holding
– Tripod or monopod mount ideal
• Measure at night for artificial sources
• Measure without and without artificial light when
measuring daylight contribution
– Capture artificial at night to differentiate contributions
clearly
• Make field holding tools and keep them handy

45. Record keeping, accuracy and precision are critical in monitoring lumen depreciation
Field Measurement

46. Record Keeping

47. TOOLS AND ACCESSORIES

48. Handy Tools
Tape
Measure
Level and
Protractor
Reference
source(s)
Color Checker and
Gray Cards
Plans
Tripod/Monopod
Any tool that will reduce variables or
eliminate interference is a good tool

49. Temperature Meters
• Contact temperature meter
– K type thermocouples
– Various contact types
– 2 channels preferable
• Ambient
• Light Source
– 4 is better
• Housing/heat sink
• Lens/diffuser
2 channel
4 channel
Note:
Non-contact IR meters
are useless for most
lighting applications
1 channel

50. Simple Flicker Checker
If you see flicker, it exists – metrics won’t change that

51. Flicker Meter
Understand what the metrics are and why they are meaningful
Multi-purpose Meter:
CCT/Lux/CRI
SVM calculations
% and index
Frequency
Modulation
Magnitude
Visual reference

52. Subjective Color Reference
• Multiple CCTs
– 2700K
– 3000K
– 3500K
– 4000K
– 5000K
• Dimmable
• Provides visual
reference and subjective
capture

53. Final Thought
Define a specific and simple procedure that controls variability, using
easy to use meters appropriate to need, and stick with it consistently
In other words… K.I.S.S.

54. This concludes The American Institute of Architects
Continuing Education Systems Course
Kevin Willmorth
Lumenique, LLC
www.lumenique.com
414-241-5124
kwillmorth@Lumenique.com