Effective Light Measurement and Data Use by Kevin Willmorth
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Transcript of Effective Light Measurement and Data Use by Kevin Willmorth
Designers Light Forum
Effective Light Measurement and Data Use
Kevin Willmorth
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 CESfor 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 ofhandling, 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.
LearningObjectives
1. Determine what can be expected from light meters2. Apply methods for increasing accuracy of
measurements 3. Determine uses of relevant data as a valuable tool4. Set up an affordable small informal lab to evaluate
product in an office5. 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:
EFFECTIVE LIGHT MEASUREMENT AND DATA USE
Lazy Metering
What’s wrong with your metering methodology?
You’re not using one!
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
9590
8580
7570
6560
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2520
1510
50
100 97 95 92 89 87 8481
7774
7167
6359
5550
4539
32
22
00
10
20
30
40
50
60
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100
100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0
Measured Light Percieved Light
Relative Perceived Illuminance
Rela
tive
Actu
al
Illum
inan
ce
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
PerceivedIlluminance
(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
Subjectivity
It’s too dark in here Wrong, too bright, I can still see you
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
Electrophot1931
Weston 6171932
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
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…
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)
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
METERS AT WORK
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”
Cosine Correction
• Cosine correction for illuminance measurements• Does not provide luminance or spot measurement
Lambert’s cosine law
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
Accuracy vs Precision
Not acceptable in professional measurement applications
Acceptable for relative measurements and comparisons only
Ideal Result
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
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
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
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 meterMay not produce a linear responseHigh precision, variable accuracy
Low accuracy, high precision –useful for relative comparisons only – extrapolating Fc data is impossible
Modern Meter Accuracy
Vs.
<$100Illuminance Only
>$2,000Illuminance + 89 other Parameters
Meters do not need to be expensive to be precise and accurate – requires verification
210215220225230235240245250255260
2700K 3000K 3500K 4000K 5000K
Illum
inan
ce
LED CCT
Meter Comparison
>$2000 <$100
All readings within +/-0.98%
Accuracy Comparison
Vs.
Analog meters disagree by >24% to one another = Poor Accuracy
A B C D EIncand 36.6 36.1 36.4 29 22Error Base 1.4% 0.5% 20.8% 39.9%
Assensetek LM-200LED Minolta T1H GE 214 GE 2175000 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
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
02700 3000 3500 4000 5000
Color Deviation
A B C Low Light C High Light
A B C
LED - Meter Error
Vs. Vs.Vs.
2700K 3000K 3500K 4000K 5000KDW58 10 22 32 45 60LM-200LED 84 84 84 84 84Minolta T-1H 83.7 84 85.1 84.1 84GE 214 45.5 47 50 50 50
0102030405060708090
Illum
inan
ce
A B C D
ABCD
Meter “D” lacks accuracy, but has good precision
Meter “A” lacks both accuracy and precision
App Base MetersDiffuser (Cosine Corrector)
Software driven readout – iOS or Android application
Multiple spectral sensor
Calibration using software
Generally offer good accuracy (if calibrated) and acceptable precision
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
Integrated Meters
Fixed sensor head can be an issue in task measurements
High end products, calibrated annually, offer high accuracy and precision
Delivered Data
CCTCRI(Ra)(R1-R8)Re(R1-15)R1~R15CQSIlluminanceFoot CandleCIE 1931CIE 1976Spectrum DiagramC78.377-2008IEC-SDCMTM-30-15(Rf, Rg & Diagram)Peak Wavelength (λp)Dominant Wavelength (λD)PurityDuvSP RatioPPFD (380~780 nm)Flicker Frequency(5-200 Hz)Flicker PercentageFlicker IndexTemperatureRelative Humidity
90+ Parameters
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
Software Interface
CCTCRI(Ra)(R1-R8)Re(R1-15)R1~R15CQSIlluminanceFoot CandleCIE 1931CIE 1976Spectrum DiagramC78.377-2008IEC-SDCMTM-30-15(Rf, Rg & Diagram)Peak Wavelength (λp)Dominant Wavelength (λD)PurityDuvSP RatioPPFD (380~780 nm)Flicker Frequency(5-200 Hz)Flicker PercentageFlicker IndexTemperatureRelative Humidity
Desktop software evaluation tools
USING METERS
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
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 = 7,500cd129.17Lux x 7.62² = 7,500cd
12Fc129.17Lux
55°
Transmission
Transmission =FC or Lux through material / FC or Lux no materialCare must be taken to avoid stray light entering sensor
Align and fix meter normal to incident angle and set distance
Fc through material = 112FcFc without material = 238Fc112/238 = 47% Transmission
Align material normal to incident angle and close to meter sensor – be wary of reflective losses
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 = 238Fc112/238 = 47% Reflectance
Distance A+C and B+C must be identical
AB
C
Incident and reflectedangles should match
Simple Benchtop Goniometer
Mount for small fixtures/lamps
Rotate in X axis in any degree steps desired with controlleror 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
Intensity and Scale
Benchtop Goniometer on steroids – the brighter and larger the source is, the larger the distances involved
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 sourceRef: 600lm Reads 36Fc
24” 24”
Reads 30Fc
600/30 = 20(Ratio of lumens per Fc measured)
B:Comparison sourceLumens???
20 x 36 = 720lm(Source B relative lumens)
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
Relative Spot Measurement
A
B
C
DE
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
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
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
Record keeping, accuracy and precision are critical in monitoring lumen depreciation
Field Measurement
Record Keeping
TOOLS AND ACCESSORIES
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
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
Simple Flicker Checker
If you see flicker, it exists – metrics won’t change that
Flicker Meter
Understand what the metrics are and why they are meaningful
Multi-purpose Meter:CCT/Lux/CRISVM calculations% and indexFrequencyModulationMagnitudeVisual reference
Subjective Color Reference
• Multiple CCTs– 2700K– 3000K– 3500K– 4000K– 5000K
• Dimmable• Provides visual
reference and subjective capture
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.
This concludes The American Institute of Architects Continuing Education Systems Course
Kevin Willmorth
Lumenique, LLC
www.lumenique.com
414-241-5124