1 Room Illuminance Measurements During TV Viewing: Pilot Study

U.S. Department of Energy

August 31, 2011

Background and Introduction

It is increasingly common for te levisions and computer monitors to include a feature called automatic brightness control (ABC ). This feature is intended to adjust screen luminance (cd/m 2 ) in response to changes in room illuminance (lux). The principle behind ABC is straightforward: all other things being equal, any display’s picture will consum e less energy and look better to the

eye 1 if its brightness is scaled in s ome fashion to the amount of a mbient light in the room. This minimizes the need for the eye to adjust rapidly to large chang es in lighting levels from one part

of the field of view to another.

In order to determine appropriat ely representative illuminance levels, it is helpful to understand the range of illuminance values o bserved in the places where pe ople watch television (TV). There are currently only limited data a vailable concerning room illum inance levels. Two key questions on this topic could benefit from further in‐field data and anal ysis:

 The first question is whether and to what extent illu minance levels in a room vary depending on where the illuminanc e measurements are taken in a given room (e.g. in the center of the room, on the couch, or at the TV). Various measurements are taken to

determine if there are variations in illuminance levels across a room

. These variations

are assessed using one

­ time static measurements taken at different locations in the room

.

 The second question is which illuminance conditions are prevalent when people watch

TV. Various measurements are also taken to determine TV viewing illuminance levels

. These viewing levels are assessed by continuously recording light levels at the TV and simultaneously recording TV on

­ times over an extended period of time (e.g. a week or more)

.

DOE has taken room illuminance mea surements as part of a nine‐h ome pilot study, the results of

which are set out in this docume nt. Although the study has all the usual limitations of a small pilot study (sample size, time d uration, seasonality, geography , multiple measurers, etc.), it has, nonetheless, yielded useful results. DOE further notes that alt hough the first question is valuable in addressing the method for mea suring room illuminance of ABC‐ enabled TVs, answering the second question (by measuring illuminance levels at the TV over time) is important in determining the room illuminance levels at which ABC‐enabled TV s should be measured.

The following section summarizes the results from the two types of measurements DOE has taken. The subsequent section se ts out the methodologies used. The next two sections set out the

1 A recent study conducted in Japan found that young and old sub jects alike preferred to i ncrease screen luminance steadily as room illuminance increased. This trend was robust a cross different average pictu re levels. See Fig. 7 in T. Matsumoto et al. (2011) “18.2: Dis tinguished Paper: Appropriate Luminance of LCD‐TV Screens under Actual Viewing Conditio ns at Home,” Society for Information Display (SID) 11 Digest , 221‐224.2 actual measurement results taken in the nine homes. Additional data from the TV viewing

illuminance level measurements a re presented in the Appendix.

Executive Summary

DOE took one‐time static room illu minance measurements at diffe rent locations in TV viewing rooms, as well as recorded light levels continuously at the TV simultaneously with TV power (to determine on‐mode operation as defined by IEC 62087‐2011), in n ine households for a week or more over a 4‐week period from mid‐May to mid‐June 2011.

A total of 144 static room illuminance measurements were made, ranging from 1 to 347 lux, with

a mean of 85 lux and a median of 46 lux.

A total of 95 TV viewing session 2 room illuminance measuremen ts were made, ranging in

duration from 10 minutes to over 5 hours. Thirty‐one, or about one‐third, of the TV viewing sessions took place during the day (defined as 6 am to 6 pm), a nd 64, or about two‐thirds, were at night (6 pm to 6 am). For daytime measurements, the range of ro om illuminance was 0 to 499 lux, with a mean of 116 lux and a median of 81 lux, whereas for nighttime measurements, the range was 0 to 106 lux, with a mean of 19 lux and a median of 1 2 lux. Across all room illuminance measurements, the mean was 51 lux and the median was 17 lux.

While limited, the TV viewing se ssion data were sufficient to s ample a variety of times of day, viewing durations and room illuminance conditions. For many hou seholds, data showed repetitive patterns of TV room i lluminance (similar times of da y, duration and room illuminance levels), indicating that with more extended measurement duratio n, average behavior might be captured. The data indicate that approximately two‐thirds of TV viewing sessions take place in the evenings, when outdoor light levels are very low or zero. D espite the observation that some people actively increase light levels when watching TV (presuma bly by turning on room lights), average nighttime room illuminance levels were significantly lo wer than during daytime. About 86 percent of TV room illuminance measurements were less than 1 00 lux.

Room illuminance levels at which ABC is measured (ABC levels) n eed to both span the range of levels at which people watch TV as well as focusing on the leve ls at which TV is most frequently viewed. The limited data available suggest that hardly any view ing occurs at 0 lux, but a large proportion of viewing instances (more than 50 percent) occur at or under 20. The data further suggest little viewing occurs abo ve 200 lux (about 5 percent), but that 300 lux seems to be a mid‐ point representation of the uppe r end of the scale. In between these two points, significant viewing occurs between 20 and 20 0 lux. These data suggest that approximately 5% of all TV viewing sessions occur between 0 and 1 lux, 50% between 1 and 2 0 lux, 20% between 20 and 50 lux, 20% between 50 and 200 lux, and 5% above 200 lux. See Figu re S1 for an illustration of these

levels.

Time‐of‐day viewing data is set out in Figures S2 and S3.

2 A TV viewing session runs from the time the TV was switched on to the time it was switched off.3 Figure S1. Cumulative Distribution of Average TV Viewing Session Room Illuminances,

with Colored Bands Indicating Candidate Illuminance Level. (Note logarithmic horizontal axis; 0 lux measurements ignored).4 Figures S2 and S3. Average Session Room Illuminance of TV Viewing Sessions. S2 (left) Split and S3 (right) stacked by time of day for comparison.

Many more measurements are nece ssary to firmly establish the av erage and range of room

illuminance levels in U.S. homes . Measurements of the same hous eholds multiple times throughout a calendar year are p robably also necessary, in orde r to capture variations in room illuminance (and possible user b ehavior) in different seasons.

Methodology

The methodology outlined below w as adopted to distinguish betwe en illuminance levels found generally in a room in which a TV is found, as compared to the conditions in that room when the TV is actually being viewed.  The se conditions can vary widely (see Results section below), depending on the degree to which sunlight enters the room.  TV watchers can modify room illuminance levels before watching TV, by adjusting window shad es or artificial light sources, or both. In order to obtain meaning ful results applicable to TV vi ewing conditions, this study

measured room illuminance with r oom lighting conditions set up by viewers the way that they are when the TV is being watched (sometimes coordinating the co rrect time of day). This study

also measured room illuminance le vels and TV power consumption simultaneously (to determine when the TV is on) for an exten ded period of time (e.g., a week or two) and correlated the data. The resulting data are useful t o assist in determining which il luminance conditions are most prevalent when people watch TVs as well as the overall range of illuminance levels at which people commonly watch TVs. Measu rements were taken at the parti cipants’ homes in the primary room where the TV is wat ched. The general characteristi cs of the room and the TV were recorded (such as brand, screen s ize, year, and technology type ).

For the measurement of static room illuminance levels , the participants were asked to set the room to the typical lighting cond itions they use to watch the T V for the time of day that the measurements were being conducte d. Light meters (Professional M easurement LX‐1128SD) were placed under various lighti ng conditions (roughly 50% dayt ime and 50% nighttime) at five different positions (defined as A through E in Figure 1 and Fig ure 2 below, adapted from Leslie &5 Conway, 1993 3 ). The measurements were taken with the illuminance meter facin g upward (toward the ceiling) and, where possible, on a tripod, at locat ions A

, B , and C , and facing outward (in the same direction as the TV screen, towards the viewer) at locations marked D and E.

Locations A through E correspond to the followi ng generic room locations:

 A was  the  center  of  the  room,  which  was  found  by  the  point  at  wh ich  two  tightly
stretched  strings  secured  to  the  corners  of  the  room  cross.    Th e  height  was  be  45

inches above the floor – the approximate height of a typical se ated TV viewer’s eyes.

 B was  the  primary  viewer’s  seated  location,  centered  left/right relative  to  the  TV’s

location and measured 45 inches above the floor.

 C was centered on the top of the TV cabinet

 D was the center of the TV screen

 E was  the  position  of  the TV’s ABC light  sensor, if available. In most  cases,  this was
near the lower left or lower right corner of the TV’s cabinet, on the front side. If a light
sensor was not present the measurement was done on the bezel (e dge of TV) on either
lower corner of the TV.  The meter was placed in a manner so as not to interfere with
the operation of the ABC light sensor itself, if ABC was enable d on the TV.

A simple sketch, similar to Figu re 2, was drawn for each room, indicating room dimensions, the locations of the TV, main seatin g area, windows, and artificial light sources, the artificial light source type (halogen, CFL, etc) and rated wattages. Locations A , B, C, D and E were marked on that sketch. Geographic location, TV diagonal screen size (in i nches), and other TV characteristics (e.g., brand, year, technology type) were also recorded. For ea ch set of test conditions, the measured illuminance values in p ositions A through E were recor ded, along with the times and dates of each measurement, outdoor lighting conditions, window shade position and lighting conditions of the room. Any other factors that may have an infl uence on the illuminance level

were also be recorded.

3 Russell P. Leslie and Kathryn M. Conway (1993), The Lighting Pattern Book for Homes , Lighting Research Center, p.

40.6 Figure 1. Three Dimensional Illumination of a Typi cal Living Room Illustrating Points D and E

for Illuminance Measurement

Figure 2. Floor Plan View/View from Above of a Ty pical Living Room Illustrating Points A, B

and C for Illuminance Measurement

For rooms with windows or receiv ing daylight from an adjacent r oom, least two sets of measurements were made:  one on a sunny day and one at night. W here possible, the measurements were repeated under different outdoor lighting con ditions (e.g., sunny, overcast), D

E

B A C7 with blinds open and closed, wit h room lighting on and off, and with the TV on and off 4 to note how the measured values changed.

The measurements were taken in a way that ensured that the meas urement technique had no significant influence on the mea surement values. The most commo n unwanted influence was in darker rooms where the person doing the measurement had the pot ential to affect the measurement by causing shadowing over the sensor or reflecting light into the sensor. For the purposes of this study a significant effect is considered to be a 10% variation between actual

illuminance and measured illumina nce. The use of a tripod and/o r a remote sensor, where possible, helped to achieve this condition.

For measurement of TV viewing session room illuminance levels , light meters were installed

on the lower bezel of TVs with t he aperture plane parallel to t he TV screen, corresponding to position E. A power meter (Elec tronic Educational Devices Watts Up Pro) was installed on the TV to simultaneously measure when the TV was on. Participants were instructed to light their rooms normally when using their TVs. Bo th meters were s et to record d ata averaged over 10‐minute intervals, in order to make seve ral measurements of room illumi nance during a typical TV viewing session.

Meters were retrieved after a mi nimum period of approximately o ne week for data download and analysis, and some households metered for two, closely‐spac ed one week periods. The

minimum of one week was chosen in order to capture both weekday and weekend viewing activity. The short duration of this pilot study did not allow for several weeks of data to be collected, which would have captured important variations in oc cupant schedules and natural light conditions (ideally, such a study would have been conduct ed repeatedly throughout a calendar year in order to capture variations in room illuminanc e in different seasons).

TV viewing sessions were defined as periods when TV electrical power exceeded the standby threshold for the TV, which was easily discernible from the dat a. The minimum, maximum and mean illuminance levels were calculated separately for each def ined viewing session. In order to identify TV viewing sessions in the light meter data accurately , the internal clocks of the illuminance meter and the power meter were synchronized to less than half the metering

interval. The clocks were also s ynchronized to within a few min utes of the local time, in order to facilitate time‐of‐day analysis of light levels and viewing hab its. These illuminance and power

data then form the event h istory of a household.

Basic demographic information, such as the number and ages of h ousehold occupants, and the

room in which the TV screen is located was collected. Screen si ze, technology (CRT, LCD, etc.), year of manufacture, brand and m odel number were also recorded. The general geographic

location was noted to enable inv estigation of regional differen ces. See Table 1.

4 Illuminance and luminance values may both change considerably with the TV on, depending on the average picture level (APL) of the s ource material.8 Results

Basic information about the nine households involved in this pi lot study is set out in Table 1 below.  The following two section s describe the results from ea ch of the two types of

measurements:

1. Variation in illuminance levels across a room – assessed using one‐time static measurements taken at different locations in the room; and

2. TV viewing illuminance levels – assessed by continuously recording light levels at the TV and simultaneously recording TV on‐times over an extended pe riod of time (e.g., a week or more).

Table 1. Basic household and TV information

House

hold # Year

manuf'd Screen

size (diag.

in.) Tech

nology

type Room in

home State Number of Full

­ Time Occupants

Total Pre

School

Children (ages 0

­ 5) Children (ages 6

­

11) Teen

agers (ages

12

­ 17) Young

Adults (ages

18

­ 34) Middle

Aged

Adults (ages 35

­ 64) Seniors (ages 65+)

1  2009  32  LCD  Living room CA  3  0  1  0  0  2  0
2  2010  40  LCD  Living room CA  2  0  0  0  2  0  0
3  2002  32  CRT  Living room CA  3  1  0  0  2  0  0
4  2009  32  LCD  Living room CO  3  0  0  0  1  1  1
5  2002  57  Projection  Living room CO  4  0  0  2  0  2  0
6  2009  40  LCD  Living room CO  2  0  0  0  0  2  0
7  2001  20  CRT  Living room CA  3  1  0  0  2  0  0

8  2009  55  LED LCD  Game room CO  2  0  0  0  0  2  0
9  2009  46  LED LCD  Living room CO  2  0  0  0  0  2  0

1. Static Room Illuminance Measurements: measuring variation in illuminance levels

across a room

Table 2 summarizes static room illuminance measurements, and Ta ble 3 provides all measurements taken along with averages and summary statistics. The mean and median room illuminance measurements, when t aking static measurements, were 85 lux and 46 lux, respectively. The mean and median room illuminance measurements at position E were 66 lux and 24 lux, respectively, somewhat less than the overall values

.

Table 2. Basic information for Static Room Illuminance Measurements

Number of households  9

Number of measurements  144 Average number of measurements per

household 16

Diagonal screen size range  20” to 57” Average room illuminance   46 lux (median), 85 lux (mean)9Table3.StaticRoomIlluminanceMeasurementsHousehold#Datein2011TimeOutsidelightconditionsBlindsRoomlightingTVLuxatlocationA(centerofroom)LuxatlocationB(viewingposition)LuxatlocationC(topcenterofTVdisplay)LuxatlocationD(centerofTVdisplay)LuxatlocationE(TVdisplaylightsensor)Mean1  5/17  18:00  overcast  closed  off  off  8  36121918  191  5/17  18:00  overcast  closed  on  off  122  41512131  531  5/17  18:00  overcast  closed  on  on  n/a  n/an/an/a31  311  5/17  18:00  overcast  open  off  off  16  1343296104  762  5/20  21:30  dark  closed  on  off  26  24171213  182  5/30  14:50  sunny  closed  off  off  78  86472524  522  5/30  15:00  sunny  closed  off  on  79  75462537  522  5/30  15:00  sunny  open  off  on  339  34711194154  2092  5/30  15:00  sunny  open  off  off  340  34611595157  2113  5/25  20:39  dark  closed  on  on  20  501515n/a  253  6/4  15:22  light overcast  closed  off  off  71  1205258n/a  754  5/26  17:00  sunny  open  off  off  43  35234039  364  6/2  21:35  dark  closed  on  on  4  8133  45  5/26  18:45  Sunny  Open  Off  On  88  1103312887  895  5/26  21:05  Dark  Closed  On  On  10  9599  85  6/2  7:45  Sunny  Open  Off  Off  54  74123131  405  6/9  19:00  sunny  open  off  on  72  673011510  595  6/9  22:30  dark  open  on  on  4  76589  205  6/9  7:30  sunny  open  off  on  90  6040155155  1006  5/23  17:00  sunny  open  off  on  215  230289259286  2566  5/23  21:00  dark  closed  on  on  22  2910911  166  5/23  17:00  sunny  open  off  on  215  230289259286  2566  5/23  21:00  dark  closed  on  on  22  2910911  167  6/3  21:30  dark  open  on  on  17  22101715  167  6/4  12:30  overcast  open  off  off  310  345333258220  2938  6/9  19:00  sunny  open  off  off  n/a  196n/an/an/a  1968  6/10  8:00  sunny  open  off  off  n/a  146n/a112n/a  1299  6/16  18:00  sunny  open  off  off  325  300n/an/an/a  3139  6/16  18:00  sunny  closed  off  off  38  38121212  229  6/16  21:00  dark  closed  on  on  25  39111111  199  6/16  21:00  dark  closed  on  off  24  38121211  199  6/16  21:00  dark  closed  off  on  3  1111  1Mean              92  108586666  8510Median              43  67202524  46Minimum              3  1111  1Maximum              340  347333259286  31311 2. TV Viewing Session Room Illuminance Measurements: measuring TV viewing

illuminance levels

Table 4 summarizes results of the TV viewing session room illum inance measurements, Table 5 provides a breakdown of each viewing session recorded, and Figu res 1‐9 summarize results in various ways.

Figure 3 and Figure 4show the number of TVs by screen size and technology type, respectively.

Figure 5 shows the distribution of TV viewing session durations , ranging from 10 minutes to more than 5 hours, with an avera ge of approximately 1.5 hours. There appeared to be a higher frequency of long TV viewing sessions (>3 hours) in the evening (defined as 6 pm to 6 am), and a higher frequency of short TV viewing sessions (< 1 hour) during the day.

Figure 6 to Figure 8 show that approximately two‐thirds of view ing sessions took place in the evening, with mean light levels much lower during evening (19 l ux) than during the day (116 lux). Viewing session room illuminance varied from 0 to almost 500 lux. As mentioned below, room illuminance at other times ( e.g., when TV was off) varied up to nearly 1,000 lux.

Figure 9 shows all TV viewing session measurements ordered by r oom illuminance to create a cumulative probability distribut ion. Because measurements are c oncentrated at low lux levels (Figure 9‐A), the data are also plotted logarithmically (Figure 9‐B) to make these low lux

measurements more discernible. A logarithmic representation als o more accurately reflects the way the eye perceives illuminance, e.g., a change from 10 to 20 lux is perceived as approximately

the same increase in relative br ightness as a change from 100 t o 200 lux. The point at which the cumulative probability reaches 5 0 percent indicates the median room illuminance level (17 lux). One sees that about 30 percent of the measurements were less th an 10 lux, and 86 percent of TV

room illuminance measurements were less than 100 lux.

Figure 10 shows example time series room illuminance data for f our households, illustrating how

room illuminance varies over the course of several days. For so me households, room illuminance varied up to nearly 1,000 lux wh en the TV was off (e.g., Figure 10‐A). In Figure 10‐B, both room illuminance and TV power are sho wn to illustrate how the coinci dent data is used to identify TV viewing sessions. Appendix A shows the remaining time series da ta not depicted in Figure 10.

From the time series data shown in Figure 10, we see that some viewers actively increased room illuminance levels when watching TV, presumably by turning on l ights (e.g., Figure 10‐B and Figure 10‐D). However, despite t his tendency, mean nighttime ro om illuminance levels were significantly lower than during the daytime. We did not, howeve r, detect decreases in daytime room illuminance during TV viewing in any of the time series.

Figure 11 shows time series room illuminance data for one house hold, plotted so that each day is aligned over the same 24‐hour period to highlight daily variati ons in viewing times and

illuminance levels. One sees cle arly, for instance, frequent ni ghttime TV viewing accompanied by increases in room illuminance (e .g., switching on lights).12 Table 4. Basic Information for TV Viewing Session Room Illuminance Measurements

Number of households  9 Number of viewing sessions  95 Average number of sessions per household  10.6 Period of metering  5/18/11 to 6/17/11 (varied with household) Average period of metering  11 days (median), 12 days (mean) Diagonal screen size range  20” to 57” Viewing duration range  0:10 to 5:30 Average viewing duration 1:30 (median), 1:42 (mean) Average viewing time of day  7:29 pm (median), 4:19 pm (mean) Number of daytime sessions (6am‐6pm)  31 Number of nighttime sessions (6pm‐6am)  64 Average daytime room illuminanc e  81 (median), 116 lux (mean) Average nighttime room illuminance  12 (median), 19 lux (mean) Average room illuminance  17 lux (median), 51 lux (mean) Daytime room illuminance range  0 to 499 lux Nighttime room illuminance range  0 to 106 lux

Table 5. TV viewing session room illuminance measurements

Household # Session # Start

date Start time Duration Average

time Mean

lux Min

lux Max lux
1  1  5/18/11  21:00  0:50  21:25  1  0  4
1  2  5/20/11  18:52  2:00  19:52  19  5  45
1  3  5/27/11  19:41  2:00  20:41  13  0  66
1  4  5/28/11  17:42  3:00  19:12  106  1  279
1  5  6/4/11  17:24  0:40  17:44  338  164  585
1  6  6/6/11  18:44  0:40  19:04  4  4  4
2  1  5/20/11  23:41  0:50  0:06  14  12  16
2  2  5/21/11  17:32  0:20  17:42  14  12  15
2  3  5/22/11  11:23  2:50  12:48  24  16  29
2  4  5/22/11  19:03  1:30  19:48  7  2  11
2  5  5/23/11  21:05  1:40  21:55  13  11  16
2  6  5/24/11  8:15  0:30  8:30  73  48  114
2  7  5/24/11  19:06  2:10  20:11  4  1  9
2  8  5/25/11  16:57  0:50  17:22  34  31  37
2  9  5/25/11  20:37  3:00  22:07  16  15  17
2  10  5/26/11  20:28  2:00  21:28  16  16  16
2  11  5/27/11  18:39  1:40  19:29  11  1  22
2  12  5/27/11  23:40  1:30  0:25  16  16  17
2  13  5/28/11  9:40  1:50  10:35  66  56  84
2  14  5/28/11  12:00  1:50  12:55  48  32  58
2  15  5/28/11  20:11  0:20  20:21  17  16  17
2  16  5/29/11  11:02  3:00  12:32  30  34  27
2  17  5/30/11  11:13  2:10  12:18  60  50  65
3  1  5/26/11  20:09  0:30  20:24  12  9  1413 3  2  5/27/11  20:15  1:00  20:45  8  0  14
3  3  5/29/11  20:13  2:20  21:23  13  4  14
3  4  5/31/11  19:59  0:50  20:24  2  0  5
4  1  5/26/11  21:17  1:40  22:07  10  3  21
4  2  5/28/11  17:17  1:50  18:12  35  22  66
4  3  5/28/11  21:37  2:40  22:57  3  3  3
4  4  5/29/11  19:47  1:50  20:42  6  2  14
4  5  5/30/11  20:07  2:40  21:27  2  1  6
4  6  5/31/11  18:07  0:20  18:17  25  23  27
5  1  5/26/11  21:43  2:00  22:43  8  0  11
5  2  5/27/11  7:43  1:10  8:18  161  109  208
5  3  5/28/11  23:53  0:30  0:08  5  1  10
5  4  5/29/11  15:33  0:20  15:43  87  81  92
5  5  5/29/11  22:43  0:40  23:03  11  10  11
5  6  5/30/11  16:53  5:10  19:28  38  1  81
5  7  5/31/11  7:43  0:50  8:08  39  99  195
5  8  5/31/11  12:33  0:20  12:43  81  80  83
5  9  5/31/11  15:13  0:50  15:38  89  82  98
5  10  5/31/11  20:33  2:00  21:33  10  0  12
5  11  6/1/11  7:43  1:00  8:13  125  59  158
5  12  6/1/11  18:53  3:10  20:28  13  9  27
5  13  6/10/11  18:24  3:10  19:59  64  2  151
5  14  6/11/11  22:04  0:10  22:09  13  13  13
5  15  6/12/11  9:44  0:10  9:49  337  337  337
5  16  6/14/11  7:24  1:10  7:59  201  142  259
5  17  6/14/11  19:04  3:10  20:39  33  1  95
5  18  6/15/11  7:34  1:10  8:09  230  165  292
5  19  6/15/11  21:34  1:30  22:19  12  0  16
6  1  5/26/11  21:00  3:00  22:30  2  0  10
6  2  5/27/11  23:50  0:40  0:10  2  0  8
6  3  5/28/11  7:50  0:20  8:00  88  81  91
6  4  5/28/11  18:40  5:00  21:10  55  10  218
6  5  5/29/11  13:00  2:30  14:15  31  5  166
6  6  5/29/11  20:30  3:10  22:05  33  25  35
6  7  5/30/11  18:40  1:50  19:35  38  0  105
6  8  5/31/11  9:30  1:50  10:25  110  2  243
6  9  6/10/11  21:30  0:50  21:55  1  0  6
6  10  6/11/11  8:50  0:20  9:00  36  19  61
6  11  6/11/11  19:50  4:10  21:55  16  0  178
6  12  6/12/11  8:50  0:50  9:15  0  0  1
6  13  6/12/11  10:00  0:40  10:20  17  1  22
6  14  6/12/11  13:50  0:20  14:00  123  119  131
6  15  6/12/11  18:40  4:10  20:45  15  0  28
6  16  6/13/11  19:40  2:30  20:55  5  3  11
6  17  6/14/11  21:10  2:40  22:30  0  0  0
7  1  6/7/11  21:16  1:10  21:51  10  9  10
7  2  6/8/11  18:07  4:50  20:32  29  10  102
7  3  6/9/11  6:37  0:20  6:47  26  21  32
7  4  6/10/11  17:29  3:30  19:14  58  11  206
7  5  6/11/11  9:20  2:20  10:30  179  87  25314 7  6  6/11/11  14:30  0:40  14:50  499  483  509
7  7  6/12/11  9:11  1:30  9:56  129  86  165
7  8  6/12/11  13:11  5:30  15:56  310  53  509
7  9  6/12/11  19:11  1:00  19:41  38  22  50
7  10  6/13/11  4:12  0:40  4:32  5  4  5
7  11  6/13/11  17:33  4:30  19:48  39  10  181
7  12  6/14/11  18:34  0:30  18:49  50  48  53
7  13  6/14/11  19:44  1:50  20:39  19  10  37
7  14  6/15/11  17:05  3:00  18:35  86  23  286
7  15  6/16/11  20:56  1:10  21:31  11  11  12
7  16  6/17/11  4:37  0:30  4:52  5  4  5
8  1  6/11/11  21:06  2:20  22:16  10  0  14
8  2  6/13/11  20:16  1:30  21:01  18  10  33
8  3  6/15/11  19:36  1:50  20:31  48  0  168
9  1  6/9/11  22:25  0:10  22:30  1  0  1
9  2  6/10/11  22:25  2:10  23:30  7  0  12
9  3  6/12/11  0:15  1:00  0:45  8  0  12
9  4  6/13/11  21:15  1:10  21:50  13  12  15
9  5  6/13/11  23:45  1:30  0:30  9  0  12
9  6  6/15/11  17:45  0:20  17:55  22  17  28
9  7  6/16/11  19:45  1:20  20:25  8  1  3915 Figure 3. Diagonal Screen Sizes of TVs in Households

Figure 4. Technology Type of TVs in Households 0 1 2 3 4

20 32 40 46 55 57Numberofhomes

Diagonal Screen Size (inches) 

## Diagonal Screen Size

0 1 2 3 4 5

CRT LCD LED LCD Projection CRTNumberofhomes 

## Technology Type16 Figure 5. TV Viewing Session Duration

(A) Split by Time of Day ( Daytime and Nighttime)

(B) Total across all measurements (stacked by Daytime and Night time)17 Figure 6Figure 4. Average Session Room Illuminance of TV Viewing Sessions

(A) Split by Time of Day ( Daytime and Nighttime)

(B) Total across all measuremen ts (stacked by Daytime and Nigh ttime)18 Figure 7. Viewing Time of Day of TV Viewing Sessions

Figure 8. Average Session Room Illumi nance versus Viewing Time of Day 0 2 4 6 8 10 12 14 16Numberofdatapoints

Time of day 

## Viewing time of day

0 100 200 300 400 500 600

0:00 2:00 4:00 6:00 8:00 10:00 12: 00 14:00 16:00 18:00 20:00 22:00 0:00AverageIlluminance(lux)

Time of Day 

## Room Illuminance by Time of Day19 Figure 9. Cumulative Distribution of Aver age TV Viewing Session Room Illuminances

(A) Absolute room illuminanc e cumulative distribution

(B) Logarithmic room illuminance cumulative distribution (0 lux measurements ignored)20 Figure 10. Room illuminance time series for selected households. Gray indicates room illuminance at all times, and black indica tes illuminance during TV viewing sessions.

(A) Household 1 (first metering week): Note high room illuminan ce during periods when TV is

off.21 (B) Household 2. Note the evenin g room lighting coinciding with TV viewing most nights, with occasional viewing at other time s with higher illuminance level s (presumably natural light). Shown are: (i) Room illumin ance and (ii) TV power.

(i)

(ii)22 (C) Household 7. In this example , viewers appear not to alter l ighting when watching TV, and viewing occurs over a wide ra nge of illuminance levels.

(D) Household 9. Example of gen erally low room illuminance, but with clear use of room lighting for TV viewing in late evenings.23 Figure 11. Daily variation in room illuminance le vels (shown for household 2 as an example).

Blue indicates room illuminance at all times, and black symbols indicate illuminance during TV viewing sessions.24 Appendix A. Other TV room illuminance data

Figure A

­ 1. Room illuminance time series for other households. Gray indicates room illuminance at all times, and bla ck indicates illuminance durin g TV viewing sessions.

(A) Household 1 (second metering week)

(B) Household 3 (note light mete r generally only switched on du ring TV viewing).25 (C) Household 4

(D) Household 5 (first metering week)26 (E) Household 5 (second metering week)

(F) Household 6 (fi rst metering week )27 (G) Household 6 (second metering week)

(H) Household 8