Jul 1, 2015 - The result will be an explicit set of equations for calculating .... abbreviated as CIE for Commission Internationale de l'Eclairage, its French name) ... It is possible to convert measurements between analogous measurements with the aid ... (unitless). Table 2.3: SI Radiometry Units. Unit bol Name. Qe joule.
PHOTOTHERAPY
INTERACTIVE INTEGRATING PHOTOMEDICINE
INTO INTERACTIVE ARCHITECTURE by
ARCHNES
PHILLIP HAMPTON EWING JR.
MASSACHUSETTS INSTITUTE OF TECHNOLOLGY
Bachelor of Architecture Auburn University, 2012
JUL 01 2015 LIBRARIES
Bachelor of Interior Architecture Auburn University, 2012
Submitted to the DepartmentofArchitecture in PartialFulfillment of the Requirementsfor the Degree of
MASTER OF SCIENCE IN ARCHITECTURE STUDIES at the
MASSACHUSETTS
INSTITUTE OF TECHNOLOGY June
2o,5
2015
Massachusetts Institute of Technology. All rightsreserved.
The author hereby grants to MITpermission to reproduce and to distributepubliclypaperand electroniccopies of this thesis document in whole or in partin any medium now known or hereaftercreated
SIGNATURE OF AUTHOR:
Signature redacted
-------------------Department of Architecture March 31, 2015
CERTIFIED BY:
Signature redacted-Kent Larson PrincipalResearch Scientist Thesis Supervisor
Signature redacted ACCEPTED BY: /V
Takehiko Nagakura
Chairof the DepartmentCommitteefor GraduateStudents
Thesis Supervisor: Kent Larson Title: Principal Research Scientist, Media Laboratory, Massachusetts Institute of Technology Thesis Reader: Takehiko Nagakura Title: Associate Professor, Department of Architecture, Massachusetts Institute of Technology Thesis Reader: Dennis Shelden Title: Associate Professor of the Practice in Computation, Department of Architecture, Massachusetts Institute of Technology
2
Interactive Phototherapy: Integrating Photomedicine into Interactive Architecture by Phillip Hampton Ewing, Jr. Bachelor of Architecture Auburn University, 2012 Bachelor of Interior Architecture Auburn University, 2012
Submitted to the DepartmentofArchitecture on March 31, 2015 in PartialFulfllment of the Requirements for the Degree of Master of Science in Architecture Studies
Abstract This thesis proposes both a physical platform and analytical model for implementing phototherapy in the context of architectural space and dynamic user behavior. By doing so, a number of problems across the fields of (i) healthcare innovation, (2) self-tracking or the "quantified self," and (3) interactive architecture would be solved. First, if healthcare systems are to gain greater insight into a number of conditions that are difficult to diagnose or treat, then passive monitoring and treatment methods must be expanded and improved. Second, if self-tracking devices are to become more accurate in monitoring and informing user health, then more contextual information about user positions and activities with reference to space are needed. Third, if interactive architectural systems are to have continuing relevance, then truly novel applications for augmenting the function of spaces must be explored. The development of a so-called "interactive phototherapy" would provide solutions by (i) increasing patient compliance to phototherapy regimens compared to more conventional methods, (2) improving the accuracy of monitoring information relevant to user health, and (3) expanding the functionality of architectural spaces to novel applications. Interactive phototherapy - a user interaction-oriented approach to phototherapy - is developed in three parts. First, we develop the CityHome, a project of the Changing Places group in the MIT Media Laboratory, as a physical platform capable of meeting technical prerequisites for the implementation of interactive phototherapy. Second, we explain a methodology for analyzing interactive phototherapy that is accessible to architectural designers and related practitioners. Third, we apply this methodology to evaluating hypothetical user interaction scenarios that may occur in the CityHome.
3
4
Acknowledgem e nts I would first like to thank the members of my thesis committee for their support throughout the development of this project. A special thanks to Kent Larson for graciously offering the opportunity to work alongside the Changing Places group in the MIT Media Laboratory on the development of the CityHome project. Prior to the development of this project, I had the opportunity to participate in a course instructed by Dennis Shelden on a course concerning architecture and the Internet of Things (IoT) - a course that was particularly helpful in the formulation of some of the ideas contained in this book. In addition, a thanks to Takehiko Nagakura for feedback and support leading up to and at key moments throughout this project. I would also like to thank my colleagues in the Design Computation and Changing Places groups for their feedback throughout this project. A special thanks to Cynthia Stewart for answering questions and resolving issues for the final submission of this book. Finally, I would especially like to thank my parents, Phillip (Sr.) and Angela Ewing, for their ongoing support leading up to throughout both this project and my time at MIT.
5
6
TABLE OF CONTENTS A bstract .......................................................................................... 3 A cknow ledgem ents ........................................................................... 5 1 / Introduction .............................................................................. 11 1. 1 Thesis Statem ent ................................................................................................................. 11 1.2 Research M otivations .......................................................................................................... I I 1. 3 Previous W ork .................................................................................................................... 12 1.4 Proposal .............................................................................................................................. 17
2
Light and M edicine .................................................................... 21 2.1 Overview ............................................................................................................................. 21 2.2 W avelength ......................................................................................................................... 21 2.3 Units of M easurement ......................................................................................................... 22 2.4 Emission Properties ............................................................................................................ 24 2.5 Eye Sensitivity to Light ........................................................................................................ 25 2.6 Physiological Responses to Light ......................................................................................... 26 2.7 Implem entation .................................................................................................................. 29 2.8 Discussion ........................................................................................................................... 31
3 / The C ityH orne Project ................................................................. 39 3.1 Overview ............................................................................................................................. 39 3.2 Contributors ....................................................................................................................... 39 3.3 Background ......................................................................................................................... 39
7
3.4 Spatial Configuration .......................................................................................................... 40 3.5 Structural/M echanical Configuration ................................................................................. 46 3.6 User Interfaces .................................................................................................................... 46 3.7 Software/Hardware Details ................................................................................................. 49 3.8 Discussion ........................................................................................................................... 50
4
Calculating Phototherapy ............................................................ 53
4.1 Overview ............................................................................................................................. 53 4.2 Background ......................................................................................................................... 53 4.3 Existing Lamp ..................................................................................................................... 55 4.4 Calculating Illuminance ...................................................................................................... 57 4.4.1 Falloff ........................................................................................................................ 57 4.4.2 Angle of Emission ...................................................................................................... 58 4.4.3 Angle of Incidence ..................................................................................................... 62 4.4.4 1 mplementatio n ......................................................................................................... 64 4.5 Illuminance to Irradiance .................................................................................................... 67 4.6 Irradiance to Dosage ........................................................................................................... 69 4.7 Discussion ........................................................................................................................... 71
5
Designing Phototherapy .............................................................. 75 5.1 Overview ............................................................................................................................. 75 5.2 Design Development ........................................................................................................... 75 5.2.1 Linear Array ............................................................................................................... 75 5.2.2 Area Array .................................................................................................................. 78 5.3 Scenario A: W aking ............................................................................................................. 80
5.3.1 Setup Param eters ....................................................................................................... 82 5.3.2 Lying in Bed ............................................................................................................... 82 5.3.3 Sitting on Sofa ............................................................................................................ 84 5.4 Scenario B: W ashing ............................................................................................................ 85 5.4.1 Setup Param eters ....................................................................................................... 87 5.4.2 Showering .................................................................................................................. 87 5.4.3 Brushing Teeth .......................................................................................................... 88 5.5 Scenario C: Working ........................................................................................................... 89 5.5.1 Setup Param eters ....................................................................................................... 91 5.5.2 Sitting at Desk ............................................................................................................ 91 5.5.3 Reading on Sofa .......................................................................................................... 92 5.6 Discussion ........................................................................................................................... 93
6 / C onclusio n ............................................................................... 97 6.1 Sum mary ............................................................................................................................. 97 6.2 Further Research ................................................................................................................. 99 6.3 Concluding Rem arks ......................................................................................................... 101
A ppendix ...................................................................................... 103 Figures .................................................................................................................................... 103 Tables ..................................................................................................................................... 105
Figure References .......................................................................... 109
Bibliography ................................................................................. III
10
1I
INTRODUCTION
1.1 Thesis Statement Phototherapy can be deployed as an interactive, user-oriented system at the architectural level in order to more effectively improve our health and promote wellness. In doing so, this so-called interactivephototherapywould be a solution to needs across the fields of (i) healthcare innovation, (2)
self-tracking, and (3) interactive architecture. First, if healthcare systems are to gain greater
insight into a number of conditions that are difficult to diagnose or treat, then continuous, noninvasive monitoring and treatment methods that can be readily deployed outside of clinical environments are needed. The emerging self-tracking or "quantified self" paradigm is one example of a category of tools poised to meet this need. Second, if self-tracking systems are to acquire more accurate, reliable data, then contextual information about a user's position, condition and/or activities are needed to supplement raw sensor data. The emerging paradigm of interactive architecture has an interest in developing tools that monitor and respond to information about a user's position, condition and/or activities within a space. Third, if interactive architectural systems are to have continuing relevance, then truly novel applications for augmenting the function of spaces must be explored. Healthcare innovation would be an example of a relatively unexplored application in interactive architecture. Thus, there is a loop of interdependencies between the fields of healthcare innovation (HI), the quantified self (QS), and interactive architecture (IA) for which a form of interactive phototherapy could be a solution.
1.2 Research Motivations Light, in the form of phototherapy, happens to be a particularly convenient modality for promoting user health - although it is by no means the only modality suitable for the task. With regards to medicine, light is arguably one of the least invasive mediums at hand. For example, the use of pulse oximetry for measuring blood oxygen (02) saturation - as well as estimating heart rate and blood pressure - has become standard use in clinical settings. The monitoring equipment involved is relatively simple: a small wearable device containing a light sensor and a pair of light sources, which is then applied to the skin. With regards to self-tracking, modified versions of the same technology can be (and have been) integrated into commercial wearable devices for monitoring heart rate throughout the day. With regards to interactive architecture, we could easily imagine information from light-based medical or self-tracking devices being transmitted to building environmental
11
control systems to modulate some relevant condition in a space - be it light, temperature, airflow, or some other phenomenon. Thus, the deployment of light as a medical device has advantages due to the relative simplicity of the equipment that may be involved. In contrast, the connotations of light in architectural discourse are deep, complex, and profound; they quickly launch off into lofty philosophical, phenomenological, psychological, and (eventually) practical considerations that are fundamental to architectural theory and practice. No beginning architecture student goes for long without hearing one of their professors deliver a lengthy exegetical lecture on what the revered
2 0 th
century architect Louis Kahn meant when he
said: "All material in nature [is] made of Light which has been spent, and this crumpled mass called material casts a shadow, and the shadow belongs to Light."' If not Kahn, then perhaps we could substitute one of his contemporaries, Le Corbusier: "Architecture is the learned game, correct and magnificent, of forms assembled in the light." 2 And if not Le Corbusier, we can substitute one of any number of influential architectural theorists and philosophers going all the way back to Vitruvius. On the other hand, the practical considerations are somewhat more explicit and concrete. There are required illumination levels required for various spaces, depending on function; there are building orientation and daylight factors to consider; there are lighting fixture types, quantities, configurations, and so on. It would be impossible to adequately give voice here to the full variety of perspectives on the role of light in architecture, but these examples may give a hint at the larger picture. It seems fair to say that the discipline of architecture is deeply concerned with how the selective deployment of light may add both subjective and objective value to space, and there is little reason to think that the deployment of light in the form of interactive phototherapy cannot align with those motivations.
1.3 Previous Work Medical knowledge of the potentially therapeutic properties of light is actually quite old, but there have been a number of technological improvements over time. Phototherapy using natural sunlight, also known as heliotherapy, is said to have been practiced in ancient Egypt, Greece, and Rome, among others. Research into modern phototherapy, however, did not develop until the late
19th
century. The Faroese physician Niels Finsen is considered to be the father of modern phototherapy. In 1903, he received the Nobel Prize in Physiology or Medicine for his work on the use of artificial light to treat conditions such as lupus vulgaris and smallpox. Over the following century, numerous methods and applications of phototherapy have been developed; various techniques may include (Lobdell, 2
2008)
(Le Corbusier, 2007) 12
multi-spectrum therapy, monochromatic therapy, or low-level laser therapy. Another technique, photodynamic therapy, uses phototherapy in combination with photoactive compounds. In addition to the visible light spectrum, ultraviolet and near infrared light may be used, depending on the application. The conditions that may be treated with phototherapy cover a broad range and includes (but is not limited to) circadian rhythm disorders, hair growth (or removal), skin conditions, pain management, and accelerated wound healing. Challenges with phototherapy as a medical tool largely involve user and/or device compliance. First, phototherapy lamps are designed to deliver a specific level of illumination at a fixed distance. Head or body movements may take the user out of the therapeutic range of the light, thus reducing the effectiveness of treatment. This problem is exacerbated with the use of smaller lamps, which in turn have tighter therapeutic ranges. Second, the user may not use the phototherapy lamp for the appropriate amount of time; if the user gets up too soon, the necessary fluence or dosage may not yet have been achieved. On the other hand, longer exposure times are not necessarily better. Many conditions are known to exhibit a biphasic dose response to phototherapy; past a certain point, prolonged exposure may generate diminished or even negative effects. Thus, the user must use the phototherapy lamp at the right distance for precisely the right amount of time. Third, variations in the performance of the lamp may also potentially negatively impact phototherapy effectiveness. Some artificial light sources may undergo a non-negligible decline in output over months or years of use. In response, some lamps may incorporate sensors and systems that self-monitor light output and increase power accordingly. Finally, there is still room for design innovations that make phototherapy usage in general more convenient. An example of such innovation in a clinical setting is the Firefly phototherapy lamp (Fig. i.),I a "cost-effective, intuitive phototherapy device designed
Fig. 1.1: Firefly phototherapy lamp. 3 (Design
that Matters, 2014) 13
to treat newborns with mild to severe jaundice in low-resource settings." By making a lamp compact enough to install in a mother's recovery room, the lamp proposes to promote in-hospital breastfeeding by the mother, as well as reduce staff workload associated with bringing a mother to a neonatal intensive care unit or monitoring a mother and newborn in separate locations. In short, there is room for improving the actual implementation of phototherapy in addition to further developing the underlying science. With regards to the quantified self and the larger "user wellness" paradigm, there have been a number of applications and devices that operate on principles related to phototherapy. For example, flux (Fig.
1.2a)
4
is a computer application that adjusts the color and brightness of a computer screen
according to the time of day and location. In doing so, the application aims to reduce eye strain and circadian rhythm or sleep disruption during evening hours. A more speculative art/architecture project, i-weather (Fig.
I.2b)5
is a website and computer-based application that uses the computer
screen as an "artificial sun" that oscillates between alertness-stimulating blue and non-stimulating orange light over a
25
hour, 7 minutes, and 40 seconds period. This, in turn, aims to allow users to
synchronize their circadian rhythms to an artificial cycle that is independent of their geographic location, a useful feature for overcoming sleep disruptions due to airplane travel and "extra-
Fig. 1.2: flux (a), i-weather (b), iluMask(c), and SunSprite (d). 4 5
(Herf & Herf, 2009) (Philippe Rahm Architects & fabric I ch,
2001)
14
terrestrial trips and holidays." Based on phototherapy used by dermatologists in clinical settings, illuMask (Fig. I.2c) 6 aims to allow users to eliminate facial acne at home by wearing a light therapy mask for 15-minutes per day. illuMask uses LEDs to radiate red and blue light, wavelengths known in the medical literature to have some effectiveness in reducing acne. SunSprite (Fig.
7
I.2d)
is a
wearable monitor and corresponding application that monitors the amount of sunlight (visible and ultraviolet) a user receives over the course of a day. By tracking and informing users about their light exposure relative to a daily goal, the tools aims to help users improve light-related conditions such as circadian rhythm disorders and some forms of depression. Although all of the aforementioned applications have merit and may be potentially helpful, it is also possible to imagine potential room for improvement upon each tool. First, the effectiveness of flux in adjusting the color temperature of a computer screen for promoting sleep hygiene is potentially irrelevant if ambient light in the room is still disruptive. Indeed, there is some common sense on the part of a user that is expected - if the user cares enough about circadian rhythm disruptions to download a program to minimize them, then they will probably also care enough not to keep all the lights on at full blast in the evening hours. In short, it would be interesting to see operation principles similar to flux applied not only to computers, but integrated into all of the other lamps in an interior environment - i.e., "smart lights." Second, the interoperability of iweatheracross different devices (indeed, any device that has an internet connection) raises questions about its effectiveness in regulating circadian rhythm - in particular, with stimulating alertness within a given exposure time. Specifics about the screen size and brightness of the device running iweather are not known to the application, nor are specifics about the user's distance from that screen known. Without these parameters, how is it possible to know if the application is providing sufficient stimulation to promote alertness within a given time frame? In defense, we do know that the brightness of a smartphone screen in the evening is sufficient enough to disrupt sleep. Even so, it would be interesting if more nuanced information about dosage parameters could be integrated into the application. Third, the anti-acne version of illuMask has been shown to be at least as effective in FDA studies as a certain "predicate device." An alternate anti-aging version of the mask, however, is completely opaque and lacks a viewport - a decision that prohibits carrying out other activities during the therapy session and potentially discourages user compliance. Of course, the apparent concern is the need for eye protection from LEDs in close proximity to the eye. Even so, one is still left to wonder whether there are ways to accommodate this need in a way that isn't as disruptive. Finally, presuming SunSprite carries out sunlight monitoring to a reasonable level of accuracy, there is a question of the interoperability of the data collected. One concern that may or may not apply to 6
(La Lumiere, LLC)
7 (GoodLux Technology, 2014)
15
SunSprite that has been noted across many self-tracking devices and applications is that the information collected is stored in a format proprietary to that application. Thus, data from one application becomes difficult to cross-compare to data from another application to generate more nuanced, holistic information about user health. Although it is not clear from the available literature whether SunSprite stores data in a proprietary format, a concern going forward for similar applications would be promoting the accessibility of collected data to other applications.
06
00
(b 24
12
0 20
(b)
Fig. 1.3: Paimio Sanatorium by Alvar Aalto (a), "sombrero" plot visualization (b). Specific contributions from the paradigm of interactive architecture to phototherapy are not completely clear yet; there is, however, evidence of concern for the health benefits of light in the larger discipline of architecture. In fact, there was once an entire category of architecture dedicated to the pursuit of plentiful sunlight and clean air to improve occupant health: the sanatorium. In the early 2oth century before the development of antibiotics, medical rationale dictated that plenty of sunlight, fresh air, rest, and good nutrition could be used to jumpstart a patient's immune system in overcoming pulmonary tuberculosis - a rationale that still makes sense, opposed to alternative conditions of the time. One of the most notable examples of sanatoria would be the Paimio Sanatorium in Finland (Fig. I-3a), designed by Finnish architect Alvar Aalto and completed in 1932. The facility featured long roof terraces for sunbathing, as well as custom fixtures and furniture specifically geared toward user health and comfort during stays which could last as long as several years. In more recent times, the Center for the Built Environment (CBE) at the University of California - Berkley has conducted extensive research to evaluating how occupants respond to the indoor environmental quality of buildings." Much of this research has involved daylighting performance in commercial buildings, and has yielded direct correlations between access to daylight and worker satisfaction and productivity: more (controlled) daylight, happier employees. Building on this trajectory of thought, others have sought to quantify the effects of lighting in spaces on 8 (Center For the Built Environment)
16
regulating biological functions. 9 A "sombrero" plot may be used to characterize the cumulative effects of ambient light at a certain point on regulating circadian rhythm (Fig. i. 3 b). A series of concentric rings are divided into quadrants, with each quadrant representing a particular view direction; inner rings correspond to earlier parts of the day. The shading of each ring quadrant corresponds with the relative potential of light from a particular direction and time of day to affect circadian rhythm. Another paradigm for analyzing space in terms of health impact is that of evidence-based design (EBD). Evidence-based design emphasizes the use of research and postoccupancy evaluations to influence design decisions. This has become a particularly popular with regards to healthcare design, and much of the evidence confirms research and approaches to lighting design from the other categories discussed. In summary, it is important to emphasize the fact that the research with regard to architectural lighting and health is (i) still ongoing and therefore incomplete to a certain extent, and (2) can only serve as guidelines to design, as opposed to explicit, prescriptive rules.
1.4 Proposal This thesis will explore the potential for interactive phototherapy, the convergence of phototherapy and interactive architecture; in order to do so, we will first need to explicitly define some terms. The Oxford English Dictionary defines phototherapy quite succinctly as: "The use of light in the treatment of physical and mental illness." Given that the field of phototherapy is relatively well-established in the medical discipline, this definition will suffice for our purposes. On the other hand, interactive architecture is a relatively new paradigm in the context of architecture, a paradigm that is heavily linked to the proliferation of computing technology. Michael Fox and Miles Kemp, in their book InteractiveArchitecture,describe it as "built upon the convergence of embedded computation (intelligence) and a physical counterpart (kinetics) that satisfies adaptation within the contextual framework of human and environmental interaction."'
To clarify, physical mechanisms
devoid of an underlying form of "intelligence" cannot be described as interactive architectural systems. Conversely, digital media projects that happen to use physical display devices are not sufficient for this definition, either. Next, Fox and Kemp goes on to echo Usman Hasque in emphasizing that interactive architecture must by definition be a two-way exchange with regards to user interaction: "A truly interactive system is a multiple-loop system in which one enters into a conversation: a continual and constructive information exchange."" Thus, we will define interactive phototherapy as a system that (i) uses light, Mardaljevic, & Lockley, (Fox & Kemp, 2009, p. 12) "(Fox & Kemp, 2009, p. 13) 9 (Andersen,
2012)
(2)
treats physical and/or mental illness, (3) is a physical
mechanism, (4) has embedded "intelligence", (5) is in continuous interaction with a human user, and (6) operates within an environmental context. With these definitions in place, we can define the structure of this thesis. In Chapter 2, we will explore to some of the basic principles of light as they may apply to phototherapy. Physical units of measurement, physiological effects of light on the body, andvarious methods of phototherapy will be discussed. In Chapter 3, we will examine the CityHome, a project of the Changing Places group in the MIT Media Laboratory, as a physical platform for interactive phototherapy. In the process of developing this thesis, I had the opportunity to collaborate with a team of researchers within the Changing Places group as an architectural designer for the project. This provided an opportunity to demonstrate that the physical systems necessary for interactive phototherapy are feasible with current technologies, as will be explored further. In Chapter 4, we will develop methods for calculating the effectiveness of interactive phototherapy, using information about an existing phototherapy lamp as a reference case. The result will be an explicit set of equations for calculating the phototherapy dosage given off by a lamp with respect to a user's location in space and time elapsed. In Chapter 5, we will propose a phototherapy installation scheme as an "add-on" for the CityHome project and analyze the performance of this scheme under various hypothetical user interaction scenarios. The performance and possible adjustments to the lighting scheme for each scenario will also be discussed. In Chapter 6, we will conclude with a summary and discuss potential directions for further development of interactive phototherapy. The contributions of this thesis will be twofold: the demonstration of a physical prototype as a platform, and the development of calculation methods for design and analysis purposes. We should clarify that none of the supporting material for these contributions, whether they be physical technology or mathematical equations, is actually new. What is (hopefully) new, however, is the realignment of this material in a new context: a vision of phototherapy (and healthcare, by extension) serving a passive, intelligent, and continuous role in our day-to-day lives.
Works Cited Andersen, M., Mardaljevic, J., & Lockley, S. W.
(2012).
A framework for predicting the non-visual effects of
daylight - Part I: photobiology-based model. Lighting Research & Technology, 44, 37-52. Center For the Built Environment. (n. d.). Centerforthe Built Environment. Retrieved December 2014, from Center for the Built Environment: http://www.cbe.berkeley.edu/
Design that Matters. (2014). Firefly- Design that Matters. Retrieved December 2014, from Design that
Matters: http://www.designthatmatters.org/firefly/ Fox, M., & Kemp, M. (2009). Interactive Architecture. New York: Princeton Architectural Press. GoodLux Technology. (2014). Wearable Sun & Light Tracker. Retrieved December 2014, from SunSprite:
https://www.sunsprite.com/tracklight/ Herf, M., & Herf, L.
(2009,
Februrary).
f lux. Retrieved
February 2014, from f.Hux: software to make your life
better: https://justgetflux.com/ La Lumiere, LLC. (n.d.). Light Therapy Mask I Anti-Wrinkle & Acne Treatment
I illuMask. Retrieved
December 2014, from illuMask: http://www.illumask.com/ Le Corbusier. (2007). Towards A New Architecture. (J. Goodman, Trans.) Los Angeles: Getty Research
Institute. Lobdell,
J. (20o8). Between Silence and Light: Spiritin the Architecture ofLouis I.
Kahn (2nd ed.). Boston:
Shambhala. Philippe Rahm Architects & fabric
I ch. (2001, October 26). i-weather.org - artificialclimate based on human
physiology. Retrieved December 2014, from i-weather: http://www.i-weather.org/
19
20
2 I LIGHT AND MEDICINE 2.1 Overview The goal of this chapter will be to explain some (but certainly not all) of the guiding principles and terminology regarding phototherapy. First, we will examine light in terms of its more independent physical properties: wavelength, various units of measurement, and source-dependent emission properties. Next, we will examine light in terms of how it affects the human body. This will include discussion of both various visual and non-visual responses and mechanisms. Finally, we will discuss
basic categories and principles regarding the implementation of phototherapy, along with some of its challenges.
2.2 Wavelength
+-
1024
1022
Y rays I
I
io-' 4
10-'6
1020
I
10-12
1018
1016
io[4
XI rays
IUV
I
io~
0-1~I0
--- ~ - -
10'
1012
IR
:10~6
I
Increasin g Frequency (v)
108
FM Microwave I
104 I
106
100
102
I
v(Hz)
Long radio waves
A
RoA.o waves
10 2
le
102
100
Increasing
I
I
I
1o 4
106
108
Wavelength (k)
X(m)
-+
Visible spectrum 1
V
B
G
R
iy~ Yeoe
o
Figure 2.1: Electromagnetic spectrum with visible light highlighted. We know that "light" refers to relatively narrow subset of electromagnetic radiation that is being emitted at frequencies that are visible to the human eye (Fig. 2.1).' It is typically characterized as having a wavelength within the range of 400 to 7oo nanometers (nm), but this is not considered to be the absolute range of human vision. Some sources define the visible band to be as narrow as 420 to '(Ronan & Gringer, 2013) 21
68o nm, 2 while others have observed it to be as short as 310 nm 3 or as long as controlled laboratory
conditions.
The International
1050
nm 4 under
Commission on Illumination (typically
abbreviated as CIE for CommissionInternationalede l'Eclairage,its French name) defines the visible light spectrum to be from 380 to 78o nm by way of its luminosity function, which will be discussed later. The International Standards Organization (ISO) has also published standards on various spectral categories for electromagnetic radiation in general. An important distinction to be made is that these categories do not always correspondwith the perceived 'color' of an object or light source, due to reasons involving the human eyes. For the purposes of this thesis, we will adopt the ISO 21348 definition (Table 2.1) for visible light spectral categories, but perform analyses over the CIE standard visible spectrum. Table 2.1: ISO 21348 Spectral Categories Sub-Category
Category Ultraviolet (UV)
Visible (VIS)
UVC
100 -280
UVB
280 -315
UVA
315 -400
Violet
380 -450
Blue
450 -500
Green
500 -570
Yellow
570 -591
Orange
591 - 610
Red
610-760
Near Infrared (NIR)
Infrared (IR)
Wavelen gth range (nm)
Middle Infrared (MIR) Far Infrared (FIR)
760
-1
400
1 400 -3 000 3 000 -1 000 000
2.3 Units of measurement Light is typically quantified in two alternative sets of SI (abbreviated SI from French: le Systeme International d'unitis) units: photometric and radiometric. Photometric measurements quantify light in terms of a human observer's ability to see it, whereas radiometric units operate in more general terms. It is possible to convert measurements between analogous measurements with the aid
2
(Laufer, 1996, p.
ii)
3 (Miyawa & Schulman, 2001, p. 187) 4 (Sliney, Wangemann, Franks, & Wolbarsht, 1976) 22
of a standardized function that models the human brightness sensitivity to different wavelengths, which will be discussed later. Some of the most common units are summarized in the included tables (Tables
& 2-3). To provide some point of reference for the photometry units - specifically
2.2
illuminance in lux (lx), as we will be using this quite frequently in later chapters - common outdoor and indoor illuminance levels are included in the appendix (Tables A- 3 and A.4, p. 1o5)Table 2.2: SI Photometry Units Quantity
Unit
Name
Symbol
Name
Symbol
Im . s
QV
lumen-second
Luminous flux
0t)V
lumen (= cd - sr)
Im
Luminous intensity
H,
candela (= lm/sr)
cd
Luminance
candela per square metre
Illuminance
lux (=lm/m
)
Luminous energy
Luminous emittance
lux(= m/m
2
cd/m2
2
)
lx
Luminous exposure
(1,
lux second
Luminous energy density
cop
lumen second per metre
Luminous efficacy
q
lumen per watt
Luminous efficiency
V
(unitless)
lx- s
lm -ms- m
3
Im/W (unitless)
Table 2.3: SI Radiometry Units Unit
Quantity Name
Sym bol
Radiant energy
Qe Oe
Radiant flux Spectral power
oe;
Radiant intensity
I,
Name
Symbol
J
joule
W
watt
watt per metre
W/m
watt per steradian
W/sr
Spectral intensity
'e
watt per steradian per metre
W-sr-1.m-1
Radiance
Le
watt per steradian per square metre
W-sr-1-m-2
Spectral radiance
Le2 or Lev
Irradiance
Ee
Spectral irradiance
/
Radiant exitance
Radiant emittancc Spectral radiant exitance / Spectral radiant emittance
watt per steradian per metre3 or watt per steradian per square metre per hertz watt per square metre watt per metre3 or watt per square metre per hertz
EeA or Me MeA or M.
watt per square metre watt per metre3 or watt per square metre per hertz
23
W/m3 or W-m22-Hz-1 2
_Wi
W/m 2 W/M
W-m
or
-Hz W/M
2
W/m3 or W-m 2 -Hz 1
Quantity Name
Unit
Symbol
Radiosity
J
Name
Symbol
watt per square metre
W/m 2 W/m
Spectral radiosity
Je,
watt per metre3
Radiant exposure Radiant energy density
He
joule per square metre
J/m 2
0),
joule per metre3
J/m 3
3
2.4 Emission Properties With the (partial) exception of lasers, most light sources cannot produce light at a single specific wavelength; instead, output occurs over a range of wavelengths. We need some method of accurately describing the compound wavelength characteristics of this light source. One way to do this is to plot out each wavelength that is being emitted by a light source along with some definition of the strength of each wavelength. We call this a spectral power distribution (SPD) curve: a plot of the absolute or relative power of light at a given wavelength for all of the wavelengths in a light source. This is a useful tool for characterizing additional information about the light source itself, especially when comparing two light sources that are considered to be "white" in coloration. What we consider to be a "white" light is another interesting topic to consider, since there are many ways to define it. One way would be to say that an ideal white light source emits equal amounts of power at all wavelengths over the visible spectrum. Indeed, it is possible for some specialized light sources to very closely approximate this via filtering and a combination of light sources with known SPDs, but this definition by and large is only theoretical when describing real-world light sources. Another way is to concede that light is not emitted perfectly evenly by natural sources, but to still describe a given light source in comparison to some equivalent "ideal" emitter. This idealized emitter is known as a "black body" emitter (for reasons that are beyond the scope of this thesis), and emits known spectral power distributions when such a body is heated to known temperatures. This is where we get the term "color temperature" when referring to white light sources; generally speaking, light sources with higher temperatures appear to be more "blue", and sources with lower temperatures appear to be more "red." The CIE has also established a series of "standard illuminants" that attempt to model commonly encountered sources of white light. Finally, we can also attempt to quantify how accurately light tends to render the colors of various objects. A color rendering index (CRI) for a light source attempts to do exactly this. A CRI value of ioo represents sunlight (for sources with a color temperature of 5,ooo K - 21,ooo K) or a blackbody emitter (
