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 televisions and computer monitors to include a feature called 

automatic brightness control (ABC). This feature is intended to adjust screen luminance (cd/m2) 

in response to changes in room illuminance (lux). The principle behind ABC is straightforward: 

all other things being equal, any display’s picture will consume less energy and look better to the 

eye1 if its brightness is scaled in some fashion to the amount of ambient light in the room. This 

minimizes the need for the eye to adjust rapidly to large changes in lighting levels from one part 

of the field of view to another.   

In order to determine appropriately representative illuminance levels, it is helpful to understand 

the range of illuminance values observed in the places where people watch television (TV). There 

are currently only limited data available concerning room illuminance levels. Two key questions 

on this topic could benefit from further in‐field data and analysis: 

 The first question is whether and to what extent illuminance levels in a room vary

depending on where the illuminance 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 one­time 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 on­times over an extended period of time (e.g. a week or more). 

DOE has taken room illuminance measurements as part of a nine‐home pilot study, the results of 

which are set out in this document. Although the study has all the usual limitations of a small 

pilot study (sample size, time duration, seasonality, geography, multiple measurers, etc.), it has, 

nonetheless, yielded useful results. DOE further notes that although the first question is valuable 

in addressing the method for measuring 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 TVs should be measured.  

The following section summarizes the results from the two types of measurements DOE has 

taken. The subsequent section sets out the methodologies used. The next two sections set out the 

                                                       

1 A recent study conducted in Japan found that young and old subjects alike preferred to increase screen luminance 

steadily as room illuminance increased. This trend was robust across different average picture levels. See Fig. 7 in T. 

Matsumoto et al. (2011) “18.2: Distinguished Paper: Appropriate Luminance of LCD‐TV Screens under Actual 

Viewing Conditions 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 are presented in the Appendix.  

Executive Summary

DOE took one‐time static room illuminance measurements at different 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 nine 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 session2 room illuminance measurements 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), and 64, or about two‐thirds, were at 

night (6 pm to 6 am). For daytime measurements, the range of room 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 12 lux. Across all room illuminance 

measurements, the mean was 51 lux and the median was 17 lux. 

While limited, the TV viewing session data were sufficient to sample a variety of times of day, 

viewing durations and room illuminance conditions. For many households, data showed 

repetitive patterns of TV room illuminance (similar times of day, duration and room illuminance 

levels), indicating that with more extended measurement duration, 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. Despite the observation that some 

people actively increase light levels when watching TV (presumably by turning on room lights), 

average nighttime room illuminance levels were significantly lower than during daytime. About 

86 percent of TV room illuminance measurements were less than 100 lux.  

Room illuminance levels at which ABC is measured (ABC levels) need to both span the range of 

levels at which people watch TV as well as focusing on the levels at which TV is most frequently 

viewed. The limited data available suggest that hardly any viewing 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 above 200 lux (about 5 percent), but that 300 lux seems to be a mid‐

point representation of the upper end of the scale. In between these two points, significant 

viewing occurs between 20 and 200 lux. These data suggest that approximately 5% of all TV 

viewing sessions occur between 0 and 1 lux, 50% between 1 and 20 lux, 20% between 20 and 50 

lux, 20% between 50 and 200 lux, and 5% above 200 lux. See Figure 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 necessary to firmly establish the average and range of room 

illuminance levels in U.S. homes. Measurements of the same households multiple times 

throughout a calendar year are probably also necessary, in order to capture variations in room 

illuminance (and possible user behavior) in different seasons. 

Methodology

The methodology outlined below was adopted to distinguish between 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.  These 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 shades or artificial light sources, or 

both. In order to obtain meaningful results applicable to TV viewing conditions, this study 

measured room illuminance with room lighting conditions set up by viewers the way that they 

are when the TV is being watched (sometimes coordinating the correct time of day). This study 

also measured room illuminance levels and TV power consumption simultaneously (to determine 

when the TV is on) for an extended period of time (e.g., a week or two) and correlated the data. 

The resulting data are useful to assist in determining which illuminance conditions are most 

prevalent when people watch TVs as well as the overall range of illuminance levels at which 

people commonly watch TVs. Measurements were taken at the participants’ homes in the 

primary room where the TV is watched. The general characteristics of the room and the TV were 

recorded (such as brand, screen size, year, and technology type).  

For the measurement of static room illuminance levels, the participants were asked to set the 

room to the typical lighting conditions they use to watch the TV for the time of day that the 

measurements were being conducted. Light meters (Professional Measurement LX‐1128SD) 

were placed under various lighting conditions (roughly 50% daytime and 50% nighttime) at five 

different positions (defined as A through E in Figure 1 and Figure 2 below, adapted from Leslie & 
5

Conway, 19933). The measurements were taken with the illuminance meter facing upward 

(toward the ceiling) and, where possible, on a tripod, at locations 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 following generic room locations: 

 A  was  the  center  of  the  room,  which  was  found  by  the  point  at  which  two  tightly 

stretched  strings  secured  to  the  corners  of  the  room  cross.    The  height  was  be  45 

inches above the floor – the approximate height of a typical seated 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 (edge 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 enabled on the TV. 

A simple sketch, similar to Figure 2, was drawn for each room, indicating room dimensions, the 

locations of the TV, main seating 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 inches), and other TV characteristics 

(e.g., brand, year, technology type) were also recorded. For each set of test conditions, the 

measured illuminance values in positions A through E were recorded, 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 influence 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 Typical Living Room Illustrating Points D and E 

for Illuminance Measurement

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

and C for Illuminance Measurement 

For rooms with windows or receiving daylight from an adjacent room, least two sets of 

measurements were made:  one on a sunny day and one at night. Where possible, the 

measurements were repeated under different outdoor lighting conditions (e.g., sunny, overcast), 

D

E

B A C
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with blinds open and closed, with room lighting on and off, and with the TV on and off4 to note 

how the measured values changed. 

The measurements were taken in a way that ensured that the measurement technique had no 

significant influence on the measurement values. The most common unwanted influence was in 

darker rooms where the person doing the measurement had the potential 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 illuminance. The use of a tripod and/or 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 the aperture plane parallel to the TV screen, corresponding to 

position E. A power meter (Electronic Educational Devices WattsUp 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. Both meters were set to record data averaged over 10‐minute 

intervals, in order to make several measurements of room illuminance during a typical TV 

viewing session.  

Meters were retrieved after a minimum period of approximately one week for data download 

and analysis, and some households metered for two, closely‐spaced 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 occupant schedules and natural 

light conditions (ideally, such a study would have been conducted repeatedly throughout a 

calendar year in order to capture variations in room illuminance 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 data. The minimum, maximum and 

mean illuminance levels were calculated separately for each defined 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 synchronized to within a few minutes of the local time, in order to 

facilitate time‐of‐day analysis of light levels and viewing habits. These illuminance and power 

data then form the event history of a household. 

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

room in which the TV screen is located was collected. Screen size, technology (CRT, LCD, etc.), 

year of manufacture, brand and model number were also recorded. The general geographic 

location was noted to enable investigation of regional differences. 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 source material.  
8

Results

Basic information about the nine households involved in this pilot study is set out in Table 1 

below.  The following two sections describe the results from each 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 period of time (e.g., a 

week or more). 

Table 1. Basic household and TV information

Household #Year

manuf'd

Screen

size

(diag.

in.)

Technology

type

Room in

home State

Number of Full­Time Occupants

Total

PreSchool

Children

(ages 0­5)

Children

(ages 6­

11)

Teenagers

(ages

12­17)

Young

Adults

(ages

18­34)

MiddleAged

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 Table 3 provides all 

measurements taken along with averages and summary statistics. The mean and median room 

illuminance measurements, when taking 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) 
9

Table 3. Static Room Illuminance Measurements

Household

#

Date

in

2011

Time

Outside

light

conditions

Blinds Room lighting TV

Lux at

location

A

(center

of

room)

Lux at

location

B

(viewing

position)

Lux at

location

C (top

center

of TV

display)

Lux at

location

D

(center

of TV

display)

L

lo

d

se

1  5/17  18:00  overcast  closed  off  off  8  36  12  19  1  5/17  18:00  overcast  closed  on  off  122  41  51  21  1  5/17  18:00  overcast  closed  on  on  n/a  n/a  n/a  n/a  1  5/17  18:00  overcast  open  off  off  16  134  32  96  2  5/20  21:30  dark  closed  on  off  26  24  17  12  2  5/30  14:50  sunny  closed  off  off  78  86  47  25  2  5/30  15:00  sunny  closed  off  on  79  75  46  25  2  5/30  15:00  sunny  open  off  on  339  347  111  94  2  5/30  15:00  sunny  open  off  off  340  346  115  95  3  5/25  20:39  dark  closed  on  on  20  50  15  15  3  6/4  15:22  light overcast  closed  off  off  71  120  52  58  4  5/26  17:00  sunny  open  off  off  43  35  23  40  4  6/2  21:35  dark  closed  on  on  4  8  1  3  5  5/26  18:45  Sunny  Open  Off  On  88  110  33  128  5  5/26  21:05  Dark  Closed  On  On  10  9  5  9  5  6/2  7:45  Sunny  Open  Off  Off  54  74  12  31  5  6/9  19:00  sunny  open  off  on  72  67  30  115  5  6/9  22:30  dark  open  on  on  4  76  5  8  5  6/9  7:30  sunny  open  off  on  90  60  40  155  6  5/23  17:00  sunny  open  off  on  215  230  289  259  6  5/23  21:00  dark  closed  on  on  22  29  10  9  6  5/23  17:00  sunny  open  off  on  215  230  289  259  6  5/23  21:00  dark  closed  on  on  22  29  10  9  7  6/3  21:30  dark  open  on  on  17  22  10  17  7  6/4  12:30  overcast  open  off  off  310  345  333  258  8  6/9  19:00  sunny  open  off  off  n/a  196  n/a  n/a  8  6/10  8:00  sunny  open  off  off  n/a  146  n/a  112  9  6/16  18:00  sunny  open  off  off  325  300  n/a  n/a  9  6/16  18:00  sunny  closed  off  off  38  38  12  12  9  6/16  21:00  dark  closed  on  on  25  39  11  11  9  6/16  21:00  dark  closed  on  off  24  38  12  12  9  6/16  21:00  dark  closed  off  on  3  1  1  1  

Mean              92  108  58  66  
10

Median              43  67  20  25  

Minimum              3  1  1  1  

Maximum              340  347  333  259  
11

2. TV Viewing Session Room Illuminance Measurements: measuring TV viewing

illuminance levels

Table 4 summarizes results of the TV viewing session room illuminance measurements, Table 5 

provides a breakdown of each viewing session recorded, and Figures 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 average 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 viewing sessions took place in the 

evening, with mean light levels much lower during evening (19 lux) 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 room illuminance to create a 

cumulative probability distribution. Because measurements are concentrated 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 also 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 brightness as a change from 100 to 200 lux. The point at which the 

cumulative probability reaches 50 percent indicates the median room illuminance level (17 lux). 

One sees that about 30 percent of the measurements were less than 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 four households, illustrating how 

room illuminance varies over the course of several days. For some households, room illuminance 

varied up to nearly 1,000 lux when the TV was off (e.g., Figure 10‐A). In Figure 10‐B, both room 

illuminance and TV power are shown to illustrate how the coincident data is used to identify TV 

viewing sessions. Appendix A shows the remaining time series data 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 lights (e.g., Figure 10‐B and 

Figure 10‐D). However, despite this tendency, mean nighttime room illuminance levels were 

significantly lower than during the daytime. We did not, however, 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 household, plotted so that each day is 

aligned over the same 24‐hour period to highlight daily variations in viewing times and 

illuminance levels. One sees clearly, for instance, frequent nighttime 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 illuminance  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  14 
13

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  253 
14

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  39 
15

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 57

Number of homes

Diagonal Screen Size (inches)

Diagonal Screen Size

0

1

2

3

4

5

CRT LCD LED LCD Projection CRT

Number of homes

Technology Type
16

Figure 5. TV Viewing Session Duration

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

(B) Total across all measurements (stacked by Daytime and Nighttime) 
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 measurements (stacked by Daytime and Nighttime) 
18

Figure 7. Viewing Time of Day of TV Viewing Sessions

Figure 8. Average Session Room Illuminance versus Viewing Time of Day

0

2

4

6

8

10

12

14

16

Number of data points

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 0:00

Average Illuminance (lux)

Time of Day

Room Illuminance by Time of Day
19

Figure 9. Cumulative Distribution of Average TV Viewing Session Room Illuminances

(A) Absolute room illuminance 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 indicates illuminance during TV viewing sessions.

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

off. 
21

(B) Household 2. Note the evening room lighting coinciding with TV viewing most nights, with 

occasional viewing at other times with higher illuminance levels (presumably natural light). 

Shown are: (i) Room illuminance and (ii) TV power. 

(i) 

(ii) 
22

(C) Household 7. In this example, viewers appear not to alter lighting when watching TV, and 

viewing occurs over a wide range of illuminance levels. 

(D) Household 9. Example of generally low room illuminance, but with clear use of room lighting 

for TV viewing in late evenings. 
23

Figure 11. Daily variation in room illuminance levels (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 A­1. Room illuminance time series for other households. Gray indicates room 

illuminance at all times, and black indicates illuminance during TV viewing sessions. 

(A) Household 1 (second metering week) 

(B) Household 3 (note light meter generally only switched on during TV viewing). 
25

(C) Household 4

(D) Household 5 (first metering week) 
26

(E) Household 5 (second metering week) 

 (F) Household 6 (first metering week ) 
27

(G) Household 6 (second metering week) 

(H) Household 8