The Pennsylvania State University The Graduate School Department of Architectural Engineering EFFECTS OF SPECTRAL MODIFICATION ON PERCEIVED BRIGHTNESS AND COLOR DISCRIMINATION A Thesis in Architectural Engineering by Minchen Wei 2011 Minchen Wei Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science August 2011 ii The thesis of Minchen Wei was reviewed and approved* by the following: Kevin W. Houser Associate Professor of Architectural Engineering Thesis Advisor Richard G. Mistrick Associate Professor of Architectural Engineering Jelena Srebric Associate Professor of Architectural Engineering Linda M. Hanagan Associate Professor and Chair of Graduate Program of Architectural Engineering *Signatures are on file in the Graduate School iii Abstract This study characterized the effect of spectral modification on perceived brightness and color discrimination under illumination provided by a pair of 32W, 4-foot, linear fluorescent lamps: SPX 3000K (SPK3K) and the Reveal® linear fluorescent (RevLF). Sixty subjects participated, with half 25 years or younger (mean = 22.5, std. dev. = 1.7) and half 60 years or older (mean = 81.4, std. dev. = 7.1). The side-by-side evaluation mode was employed to characterize perceived brightness. Subjects made a forced choice for each of 44 pairs of light settings that: were practice trials (4 pairs); differed in spectrum at equal illuminance (8 pairs); varied in both spectrum and illuminance (24 pairs); or were identical (i.e. null condition trials, 8 pairs). Light settings were set within a range of 240 to 330 lux and the rooms had neutral gray surfaces. Equal perceived brightness was inferred from the paired comparisons, and found to occur when the photopic quantity (e.g. illuminance, luminance) from the RevLF was 5% lower (younger subjects) or 8% lower (older subjects) than that provided by the SPX3K lamps. At equal illuminance of 330 lux, the room illuminated by the RevLF was preferred to the one illuminated by the SPX3K by 67% of the younger subjects and 73% of the older subjects. Color and brightness were most commonly cited as reasons for preference. Color discrimination was characterized under 300 lux of RevLF and SPX3K illumination using the Farnsworth-Munsell 100 Hue Test (FM-100). For color-normal people below 25 years of age, and for those above 60 years of age who had cataract surgery, the red-green partial error score was statistically better under RevLF illumination. A significant difference was not found in the blue-yellow partial error score or in the total error score. iv When brightness perception is considered in isolation, the spectral advantages of the RevLF cannot be offset by the disadvantage of lower luminous efficacy. That is, these data suggest that at equal brightness a room illuminated with RevLF will consume more energy than an otherwise identical room illuminated with SPX3K. When brightness and color discrimination are considered together, as with visual clarity, it is unknown whether RevLF or SPX3K illumination would be more energy efficient. Color discrimination, brightness perception, and overall preference all play a role in occupants‘ gestalt evaluation, contribute to high performance building interiors, and play a role in sustainable lighting solutions designed to address occupant needs. v TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................................... vii LIST OF TABLES ........................................................................................................................ xi Acknowledgements ..................................................................................................................... xiii Chapter 1 Introduction.................................................................................................................. 1 1.1 Background ................................................................................................................................ 1 1.1.1 The Human Eye ...................................................................................................................... 1 1.1.2 Color ....................................................................................................................................... 6 1.1.3 Theories of Color Vision ...................................................................................................... 12 1.1.4 Changes with Age ................................................................................................................. 15 1.2 Objective .................................................................................................................................. 18 1.3 General Approach .................................................................................................................... 19 Chapter 2 Literature Review ...................................................................................................... 20 2.1 Lamp SPD Vs. Spatial Brightness ........................................................................................... 20 2.2 Experimental Methods for Brightness Perception ................................................................... 28 2.3 Color Discrimination ............................................................................................................... 30 2.4 Spectral Modification ............................................................................................................... 33 Chapter 3 Design of the Study and Methodology ..................................................................... 36 3.1 Apparatus ................................................................................................................................. 36 3.2 Subjects .................................................................................................................................... 39 3.3 Independent Variables ............................................................................................................. 40 3.3.1 Independent Variables for Perceived Brightness .................................................................. 40 3.3.2 Independent Variables for Color Discrimination .................................................................. 47 3.4 Dependent Variables ................................................................................................................ 47 vi 3.4.1 Dependent Variables for Perceived Brightness..................................................................... 47 3.4.2 Dependent Variables for Color Discrimination .................................................................... 47 3.5 Statistical Design ..................................................................................................................... 48 3.5.1 Statistical Design for Perceived Brightness .......................................................................... 48 3.5.2 Statistical Design for Color Discrimination .......................................................................... 51 3.6 Experimental Procedures ......................................................................................................... 51 Chapter 4 Analysis and Results .................................................................................................. 54 4.1 Data Reliability: Null Condition Trials and Tests for Bias ...................................................... 54 4.2 Perceived Brightness ................................................................................................................ 58 4.3 Color Discrimination ............................................................................................................... 71 Chapter 5 Discussion ................................................................................................................... 77 5.1 Perceived Brightness ................................................................................................................ 77 5.2 Color Discrimination ............................................................................................................... 85 Chapter 6 Conclusions ................................................................................................................. 91 Reference ...................................................................................................................................... 92 vii LIST OF FIGURES Figure 1-1 | A drawing of a section through the human eye [1] .............................................. 1 Figure 1-2 | A simple diagram of the organization of the retina [1] ........................................ 3 Figure 1-3 | Distribution of rods and cones in the retina [4] .................................................... 3 Figure 1-4 | Luminous efficiency functions recognized by CIE [8] ........................................ 5 Figure 1-5 | Normalized cone fundamentals and photopigment sensitivities [8] ..................... 6 Figure 1-6 | RGB color matching functions [8] ....................................................................... 8 Figure 1-7 | XYZ color matching functions [8] ....................................................................... 8 Figure 1-8 | The CIE 1976 USC with isotemperature lines ..................................................... 9 Figure 1-9 | Organization of Munsell Color System ................................................................ 11 Figure