Revisiting Visual Comfort in the Digital Age by John Katimaris

1. Designers Light Forum
Revisiting Visual Comfort in the Digital Age
John Katimaris
New York School of Interior Design
Program Director | School of Continuing and Professional Studies
Program Director | Master of Professional Studies I Lighting Design
170 East 70th Street New York NY 10021
212 472 1500 Extension 210 516 721 2969
jkatimaris@nysid.edu
www.nysid.edu
March 29 2017
8:30 AM – 9:30 AM
New York Hilton Midtown

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
At the end of the this course, participants will be able to recognize: Program Mission
Efficient luminaires can cause discomfort glare
as extremely high levels of luminaire surface
brightness may require unpleasant eye
adaptation. Energy code compliance compels
the development of high efficiency LED
luminaires – perhaps with little regard for glare
control. Through understandable comparative
analysis, this presentation explores the
relationship between luminous efficiency and
visual comfort in our increasingly digitally
illuminated interior environments.
1. Vision Geometry
2. Glare Gamut
3. Visual Comfort Limit
4. Visual Comfort Probability
5. Unified Glare Rating
6. Luminance Data
The amount of time spent on particular topics / sections / slides will vary throughout this presentation.

4. 45 degrees 55 degrees 65 degrees 75 degrees 85 degrees
0
500
1000
1500
2000
2500
3000
3500
4000
4500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Comparative Luminance
2570
1850
1285
857
600
3950
3600
3460
2870 2500
Exit Lumens
Visual Comfort Benchmarking
59.1%
57.2%
59.8%
81.0%
96.0%
Beginning at the end ensures
The presentation is completed on time!

5. Epilogue
There is a need to better recognize the influence
of the luminance (brightness) characteristics of
both uniform and non-uniform luminaires on the
experience of glare. Efficient luminaires can
cause discomfort glare as extremely high levels
of luminaire surface brightness may require
unpleasant eye adaptation. Energy code
compliance compels the development of high
efficiency LED luminaires – perhaps at the
expense of understanding the organics of visual
comfort.
As with most standards, minimum
requirements are laid down.
Standard compliant lighting is no
guarantee in itself for good lighting.
For this, application understanding,
product understanding, and understanding
the situation are required.
Conclusion: The 3 U’s

6. Geometrics | Photometrics | Optometrics

7. 25 watt sphere = 110 lumens
60 watt sphere = 550 lumens
100 watt sphere = 1050 lumens
Circle @ 19.63 = 25% Sphere @78.54
25 watt hemi-sphere = 55 lumens
60 watt hemi-sphere = 275 lumens
100 watt hemi-sphere = 525 lumens
32 watt right cylinder = 3000 lumens
28 watt right cylinder = 2750 lumens*
54 watt right cylinder = 4725 lumens*
Rectangle @ 23.19 = 16% Right Cylinder @ 147.26
*Rectangle @ 13.98 = 16% Right Cylinder @ 88.49
32 watt right hemi-cylinder = 1500 lumens
28 watt right hemi-cylinder = 1375 lumens
54 watt right hemi-cylinder = 2363 lumens
Geometrics | Photometrics | Optometrics

8. 25 watt sphere = 110 lumens
60 watt sphere = 550 lumens
100 watt sphere = 1050 lumens
Circle @ 19.63 = 25% Sphere @78.54
25 watt hemi-sphere = 55 lumens
60 watt hemi-sphere = 275 lumens
100 watt hemi-sphere = 525 lumens
32 watt right cylinder = 3000 lumens
28 watt right cylinder = 2750 lumens*
54 watt right cylinder = 4725 lumens*
Rectangle @ 23.19 = 16% Right Cylinder @ 147.26
*Rectangle @ 13.98 = 16% Right Cylinder @ 88.49
32 watt right hemi-cylinder = 1500 lumens
28 watt right hemi-cylinder = 1375 lumens
54 watt right hemi-cylinder = 2363 lumens
Vanity light bars available in
4 watts per foot of LEDs to create 300 lumens per foot
6 watts per foot of LEDs to create 465 lumens per foot
8 watts per foot of LEDs to create 600 lumens per foot
300 lumens per foot x 3 feet = 900 lumens
465 lumens per foot x 3 feet = 1395 lumens
600 lumens per foot x 3 feet = 1800 lumens
900 lumens = 172% of a 100 watt incandescent hemi-sphere
1395 lumens = 266% of a 100 incandescent watt hemi-sphere
1800 lumens = 343% of a 100 incandescent watt hemi-sphere
900 lumens = 60% of a 32 watt fluorescent hemi-cylinder
1395 lumens = 93% of a 32 watt fluorescent hemi-cylinder
1800 lumens = 120% of a 32 watt fluorescent hemi-cylinder
Geometrics | Photometrics | Optometrics

9. Critical Thinking – More Necessary Now Than Ever
Knowledge versus Understanding
We live in a world saturated with information.
We have virtually unlimited amounts of data at our fingertips at all times, and we’re
well versed in the arguments
about the dangers of not knowing enough and not doing our homework.
But what I have sensed is an enormous frustration with the unexpected costs of
knowing too much, of being inundated with information.
We have come to confuse information with understanding.
... Malcolm Gladwell
We’ve created more human-made information in the last five years than in all of
human history before then.
… Daniel J. Levitin
It ain’t what you don’t know that gets you into trouble.
It’s what you know for sure that just ain’t so.
… Mark Twain

10. Daily Aggregate Techno-Light Stimuli

11. Photonics: Why Light Matters
On the most fundamental level through photosynthesis, light is necessary to the existence of life itself, and the many applications
of light have revolutionized society through medicine, communications, entertainment and culture.
Light and photonics are poised to become key enabling technologies of the future.
http://www.light2015.org/Home/WhyLightMatters.html
http://time.com/3257927/you-asked-can-computers-ruin-eyes/
The average American (age 16 – 44) spends 444 minutes
(7.4 hours) staring at digital screens everyday.
The Bureau of Labor Statistics puts the average night’s sleep for an American (age 25 – 54) at 7.7 hours.
The Vision Council reports reveals a third of adults spend more than
9 hours everyday on digital devices
http://www.digitaltrends.com/mobile/does-your-phone-damage-your-eyes-an-experts-advice/

12. Photonics: Why Light Matters
The light from LEDs, or light-emitting diodes, comes primarily from the short-wave, high-energy blue and
violet end of the visible light spectrum.
Prolonged, continuous exposure to this light, from computer monitors, mobile phones and television screens or indoor and outdoor
lights may be enough to damage retinas.
This problem is going to get worse, because humans are living longer* and children are using electronic devices
from a young age particularly for schoolwork.
Eyes are not designed to look directly at light — they are designed to see with light
… Dr. Celia Sánchez-Ramos
Chair: Celia Sánchez-Ramos, Professor at the Department of Optometry and Vision, Universidad Complutense de Madrid.
http://www.livescience.com/31949-led-lights-eye-damage.html
http://time.com/3257927/you-asked-can-computers-ruin-eyes/
*Life expectancy has increased for
fifty and sixty year olds today – by
about ten years compared to 1850
A Field Guide to Lies
Daniel J. Levitin

13. Unified Glare Rating (UGR) values generally range from 10 to 30.
A high value indicates significant discomfort glare, and a low value indicates little discomfort glare.
Electric lighting systems producing UGR values of 10 or less are assumed to produce no discomfort.
The CIE definition of Discomfort Glare is glare that causes discomfort without necessarily impairing the vision of objects.
Glare which impairs the vision of objects is termed Disability Glare and is not covered in this metric.
http://docs.agi32.com/AGi32/Content/adding_calculation_points/Calculations_UGR_Concepts.htm
Visual Comfort Probability (VCP) is a measure of discomfort glare for interior lighting applications.
According to the IES Handbook, 9th Edition:
The visual comfort probability (VCP) is the probability that a normal observer does not experience discomfort when viewing a
lighting system under defined conditions.
This system was tested and validated using lensed direct fluorescent systems only.
VCP should not be applied to very small sources such as incandescent and high-intensity discharge luminaires, to very large
sources such as ceiling and indirect systems, or to non-uniform sources such as parabolic reflectors." With these caveats in mind,
UGR can be correlated with VCP for lighting systems that consist of luminaires that fall within the scope of the definition of VCP.
Unified Glare Rating | Visual Comfort Probability

14. http://docs.agi32.com/AGi32/Content/adding_calculation_points/Calculations_UGR_Concepts.htm
UGR Discomfort Glare Criterion
10 Imperceptible
13 Just perceptible
16 Perceptible
19 Just acceptable
22 Unacceptable
25 Just uncomfortable
28 Uncomfortable
UGR VCP Equivalent
11.6 90%
16 80%
19 70%
21.6 60%
24 50%
Unified Glare Rating | Visual Comfort Probability
Discomfort glare is at the epicenter of the
Unified Glare Rating and
Visual Comfort Probability metrics

15. Visual comfort is considered an important quality measure for indoor
functional lighting and prevention of discomfort glare.
LED based lighting systems offer many different design options and it is
no surprise that fixtures with highly non-uniform luminance patterns
appear on the market.
The currently used formulae to predict discomfort glare
(UGR or VCP) are still based on conventional light sources with much
more homogeneous luminance patterns.
However, studies done in laboratory settings showed that point array
LED luminaires may provoke more discomfort glare than uniform
sources.
https://www.led-professional.com/technology/light-generation/discomfort-glare-perception-of-non-uniform-light-sources-in-an-office-setting
Geometrics | Photometrics | Optometrics

16. The macula is divided into 6 regions –
umbo | foveola | foveal avascular zone or FAZ | fovea | parafoveal | perifovea
Visual acuity declines by about 50% every 2.5 degrees from the center up to 30 degrees at which point visual acuity
declines more steeply. 30 degrees is thus taken as the dividing line between adequate and poor color perception.
https://en.wikipedia.org/wiki/Peripheral_vision#/media/File:Peripheral_vision.svg
https://en.wikipedia.org/wiki/Peripheral_vision#/media/File:Field_of_view.svg
https://www.quora.com/What-is-foveal-vision
Besharse, Joseph C.; Bok, Dean (2011). The Retina and Its Disorders. Academic Press.
Abramov, Israel; Gordon, James; Chan, Hoover (1991).
Color appearance in the peripheral retina: effects of stimulus size. Journal of the Optical Society of America
Back to Basics: The Geometry of Vision

17. https://www.quora.com/What-is-foveal-vision
Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
Foveal vision is used loosely to refer to any sort of central vision, with a wide variety of conflicting definitions.
Foveal Vision (<2 degrees) | Central Vision (5 degrees) | Paracentral Vision (8 degrees) | Macular Vision (18 degrees)
Peripheral vision is used loosely to refer to what in technical usage would be called far peripheral vision.
Near Peripheral Vision (30 degrees) | Mid Peripheral Vision (60 degrees) | Far Peripheral Vision (100 degrees – 110 degrees)
Back to Basics: The Geometry of Vision
ies_037.pdf

18. Glare is a sensation caused by brightness within the visual field that
is sufficiently greater than the luminance to which the eyes are adapted.
The result can be annoyance, discomfort, and decreased visual performance.
It is subjective (sparkle / dazzle) and sensitivity to glare can vary widely.
A given bright light may or may not produce glare depending upon –
 The location and intensity of the light source
 The clarity of the media of the eye
 The state of adaptation of the eye
 The background luminance
http://medical-dictionary.thefreedictionary.com/glare
A
B
C
D
Experiencing Glare: Benchmarking Subjectivity

19. Direct Glare
Glare produced by a source of light situated in the same or nearly the
same direction as the object of fixation.
Eccentric Glare or Indirect Glare
Glare produced by an intense light source situated in a
direction other than that of the object of fixation.
Disability Glare
Glare which reduces visual performance without
necessarily causing discomfort.
Discomfort Glare
Glare which produces discomfort without necessarily interfering
with visual performance.
http://medical-dictionary.thefreedictionary.com/glare
A
B
C
D
Experiencing Glare: Benchmarking Subjectivity

20. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
Visual comfort limits for glare depend on the relationship
of brightness and size of the source, the position of the
object in the visual field, and the eye adaptation of the viewer.
The sketch shows generally acceptable average luminance
levels for different angles of incidence.
Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
Luminance indicates how much luminous power will be detected
by an eye looking at the surface from a particular angle of view.
Luminance is thus an indicator of how bright the surface will appear.
A typical HDTV emits between 250 and 400 candela / square meter
(73 and 117 foot lambert)
http://www.jakeludington.com/ask_jake/20100512_what_is_cdm2_on_a_monitor_or_hdtv.html
Visual Comfort Limits

21. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
VCP values are frequently associated with luminaires under standardized conditions of use.
1. An initial average horizontal illuminance of 100fc (1000lx)
2. Room reflectance of .80 (ceiling) .50 (wall) .20 (floor)
3. Luminaire mounting heights above floor of 8.5’, 10.0’, 13.0’ and 16.0’
4. A given range of room dimensions including square, long narrow, and short wide rooms
5. An observation point of 4’ in front of the center of the rear wall and 4’ above the floor
6. A horizontal line of sight, directly forward
7. An upward limit to the field of view corresponding to an angle of 53 degrees*
above and directly forward from the observer
IESNA Lighting Handbook Reference & Application 9th Edition
*Mid peripheral vision
Visual Comfort Limits

22. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company https://www.ies.org/PDF/100Papers/037.pdf
The scissors curve (circa 1956) describes the graph of limiting brightness for school and office lighting.
“It was never intended that the scissors curve continue indefinitely. It was the best that we had with the knowledge that was available.
It is anticipated that in the not too distant future, it will be superseded by a much better criterion”
C.L.Crouch
Background and Use of Scissors Curve
IES Journal June 1965
Discomfort Glare: Scissors Curve Infographic

23. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
Discomfort glare from luminaires can be
controlled by limiting brightness (luminance).
To control direct glare, values of measured luminaire
brightness should fall below the limit lines.
Discomfort Glare: Scissors Curve Infographic

24. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
The visual comfort probability of a lighting system
(expressed as a percentage from 0 -100) is an estimate of people who do not
find a lighting system uncomfortable from a glare perspective.
The VCP system was developed based on research which
considered glare from lensed fluorescent lighting systems.
http://www.tandfonline.com/doi/abs/10.1080/00994480.1999.10748278?journalCode=uzie20
For most observers with normal glare sensitivity, the following describes
the glare sensation corresponding to VCP rating:
95% – 100% Unnoticeable
75% – 94% Acceptable
64% – 74% Distracting, but not uncomfortable
50% – 63% Threshold of discomfort
34% – 49% Uncomfortable
20% – 33% Perceptibly uncomfortable
The VCP does not rate the overall acceptance of the visual environment.
Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
*candela per square meter
Discomfort Glare: Scissors Curve Infographic

25. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
2570*
1850*
1542*
1285*
857*
*candela per square meter
600*
Discomfort Glare: Scissors Curve Infographic

26. 0
500
1000
1500
2000
2500
3000
3500
4000
4500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Recommended Visual Limits
85 degrees75 degrees65 degrees55 degrees45 degrees
2570
1850
1285
600
857
Discomfort Glare: Scissors Curve Infographic

27. Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
Baffles, louvers, perforated panels, and sheet acrylic (to a lesser degree) can provide shielding for lamps to prevent glare.
The shielding angle (in degrees) is the maximum angle between the horizontal and the observer’s line of sight
to the shielding materials when the lamps first can be seen.
Shielding to Prevent Glare

28. The table below presents example direct glare conditions
and efficiencies for a variety of shielding materials used in
typical 2’ x 4’ recessed fluorescent luminaires.
Luminaire efficiency (usually expressed as a percentage)
relates the lumens emitted by the luminaire (exit lumens)
to the lumens emitted by the lamps.
Shielding
Method
Direct Glare
Condition
Luminaire
Efficiency
Concepts in Architectural Lighting / M. David Egan / McGraw-Hill Publishing Company
Shielding to Prevent Glare

29. http://www.tandfonline.com/doi/abs/10.1080/00994480.1990.10747960?journalCode=uzie20
http://www.lightsearch.com/resources/lightguides/glare.html
“The VDT screen is recognized as a unique visual task in
terms of shape, orientation, luminance, and reflectance.
The increasing emphasis on visual display terminal tasks
has brought about a resurgence of concern about
environmental influences on worker comfort, productivity,
and even safety.”
Glare Evaluation Calculations Applied to Visual Display Terminals
Journal of the Illuminating Engineering Society
Summer 1996
Shielding to Prevent Glare

30. Viewing Angle Dynamics
UGR > 23 UGR < 19

31. Prismatic Acrylic Lens Fluorescent Luminaire
6100 Total Lamp Lumens 3603 Exit Lumens
59.1% Efficiency
.430 Average Coefficient of Utilization
Average Luminance
376 FL (1288)* @ 45 degrees
252 FL (863)* @ 55 degrees
200 FL (685)* @ 65 degrees
203 FL (696)* @ 75 degrees
202 FL (692)* @ 85 degrees
*candela per square meter
Extrapolating Visual Comfort Performance

32. Parabolic Louver Fluorescent Luminaire
5870 Total Lamp Lumens 3461 Exit Lumens
57.2% Efficiency
.424 Average Coefficient of Utilization
Average Luminance
435 FL (1490)* @ 45 degrees
369 FL (1264)* @ 55 degrees
74 FL (254)* @ 65 degrees
27 FL (93)* @ 75 degrees
25 FL (86)* @ 85 degrees
*candela per square meter
Extrapolating Visual Comfort Performance

33. Center Barrel Fluorescent Luminaire
4800 Total Lamp Lumens 2871 Exit Lumens
59.8% Efficiency
.403 Average Coefficient of Utilization
Average Luminance
770 FL (2637)* @ 45 degrees
788 FL (2702)* @ 55 degrees
831FL (2846)* @ 65 degrees
851 FL (2917)* @ 75 degrees
500 FL (1712)* @ 85 degrees
*candela per square meter
Extrapolating Visual Comfort Performance

34. 0
500
1000
1500
2000
2500
3000
3500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Comparative Luminance
Series1 Series2 Series3
2570
1285
857
600
1850
45 degrees 55 degrees 65 degrees 75 degrees 85 degrees
Visual Comfort Benchmarking
59.1%
57.2%
59.8%

35. Claims, claims and more claims…
Delivered Lumens
represents lumens that are projected from a lamp or luminaire.
These are the actual working lumens projected toward
the horizontal or vertical plane.
Sometimes these are also called useful lumens, real lumens,
or exit lumens.
http://www.eli.com.au/content/breaking-down-led-output-data-total-lumens-vs-delivered-lumens
When looking at the light output that does reach the application area after being reflected,
consider that energy is lost and compounded with every reflection.
http://www.premierltg.com/total-lumens-vs-delivered-lumens/
The New Luminaire Narrative

36. Ultra-thin form factor maximizes your ceiling
space and installs easily in very shallow
ceiling plenums.
These modern general lighting fixtures
produce highly efficient, aesthetically
pleasing diffused light with minimal glare.
The New Luminaire Narrative

37. Flat Panel LED Luminaire
3946 Exit Lumens
81% Efficiency
.706 Average Coefficient of Utilization
Average Luminance
1124 FL (3850)* @ 45 degrees
1039 FL (3560)* @ 55 degrees
932 FL (3192)* @ 65 degrees
737 FL (2524)* @ 75 degrees
354 FL (1212)* @ 85 degrees
*candela per square meter
Extrapolating Visual Comfort Performance

38. 45 degrees 55 degrees 65 degrees 75 degrees 85 degrees
0
500
1000
1500
2000
2500
3000
3500
4000
4500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Comparative Luminance
2570
1850
1285
857
600
Visual Comfort Benchmarking
59.1%
57.2%
81.0%
59.8%

39. Center Barrel LED Luminaire
2507 Exit Lumens
96% Efficiency
.685 Average Coefficient of Utilization
Average Luminance
676 FL (2315)* @ 45 degrees
670 FL (2294)* @ 55 degrees
681 FL (2332)* @ 65 degrees
712 FL (2439)* @ 75 degrees
643 FL (2203)* @ 85 degrees
*candela per square meter
Extrapolating Visual Comfort Performance

40. 45 degrees 55 degrees 65 degrees 75 degrees 85 degrees
0
500
1000
1500
2000
2500
3000
3500
4000
4500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Comparative Luminance
2570
1850
1285
857
600
3950
3600
3460
2870 2500
Exit Lumens
Visual Comfort Benchmarking
59.1%
57.2%
59.8%
81.0%
96.0%

41. Epilogue
There is a need to better recognize the influence
of the luminance (brightness) characteristics of
both uniform and non-uniform luminaires on the
experience of glare. Efficient luminaires can
cause discomfort glare as extremely high levels
of luminaire surface brightness may require
unpleasant eye adaptation. Energy code
compliance compels the development of high
efficiency LED luminaires – perhaps at the
expense of understanding the organics of visual
comfort.
As with most standards, minimum
requirements are laid down.
Standard compliant lighting is no
guarantee in itself for good lighting.
For this, application understanding,
product understanding, and understanding
the situation are required.
Conclusion: The 3 U’s

42. This concludes The American Institute of Architects Continuing
Education Systems Course