# ANALYSIS OF ROOM ILLUMINANCE AND

TELEVISIONS WITH AUT OMATIC BRIGHTNESS CO NTROL :

ENERGY EFFICIENCY PROGRAM FOR CONSUMER

PRODUCTS:

Television Sets

March 2012

U.S. Department of Energy

Assistant Secretary

Office of Energy Efficiency and Renewable Energy

Building Technologies Program

Appliances and Commercial Equipment Standards

Washington, DC 20585

### This Document was prepared for the Department of Energy

by staff members of

Lawren ce Berkeley National Laboratory1 

### ANALYSIS OF ROOM ILLUMINANCE AND

TELEVISIONS WITH AUT OMATIC BRIGHTNESS CONTROL

TABLE OF CO NTENTS

1.1 INTRODUCTION ...............................................................................................................3

1.2 COMPARISION OF ROOM ILLUMINANCE STUDIES .................................................5

1.2.1 Time of Day .........................................................................................................................5

1.2.2 Range of Illuminance Measurements per Event ..................................................................7

1.2.3 Range of Illuminance Measurements per Hour ...................................................................9

1.2.4 Comparison Between Weekday and Weekend ..................................................................10

1.2.5 Room Illuminance with the TV On or Off.........................................................................13

1.3 TESTING TELEVISIONS WITH ABC ............................................................................17

1.3.1 Ideal Behavior ....................................................................................................................17

1.3.2 Testing Results ...................................................................................................................18

1.4 DISCUSSION ....................................................................................................................26

1.5 SUMMARY .......................................................................................................................29

APPENDIX: LATEST TES TING METHODOLOGY .................................................................31

LIST OF TABLES

Table 1.2.1 Day and night time hours in the CLASP study by location .....................................6

Table 1.2.2 Mean room illuminance vs. cumulative event fraction ............................................8

Table 1.2.3 Mean room illuminance vs. cumulative viewing hours .........................................10

Table 1.3.1 Summary table of DOE, ENERGY STAR and CLASP TV power and

luminance testing. No color: Power measured at 0, 10, 100, 150, and 300

lux, no luminance measurements; Blue: Power and luminance measured at

0, 10, 30, 50, 100, 150, and 300 lux; Green: Power and luminance

measured at 10, 50, 150 and 300 lux. ....................................................................19

Table 1.4.1 Power measured at additional room illuminance levels between 0-300 lux

for seven 2011 TV models. ....................................................................................28

Table 1.4.2 Percent change in power calculation methods from ENERGY ST AR

methodology. .........................................................................................................292 

### LIST OF FIGURE

Figure 1.2.1 Time of day distribution in the CLASP data ...........................................................5

Figure 1.2.2 Time of day distribution in the LBL data ................................................................6

Figure 1.2.3 Time of day distribution in the CEA data ................................................................6

Figur e 1.2.4 Distribution of television viewing times from the 2010 ‘American Time

Use Survey’ ..............................................................................................................7

Figure 1.2.5 Comparison of room illuminance cumulative distributions of the 3 sets of

data. Data are averaged over viewing events. ..........................................................8

Figure 1.2.6 Room illuminance per hour of TV viewing .............................................................9

Figure 1.2.7 CLASP study data points by type of day ...............................................................11

Figure 1.2.8 Normalized CLASP study data points by type of day ...........................................11

Figure 1.2.9 LBL data points by type of day..............................................................................12

Figure 1.2.10 Normalized LBL data points by type of day ..........................................................12

Figure 1.2.11 CLASP lux by time and type of day when TV was on ..........................................13

Figure 1.2.12 LBL lux by time and type of day when TV was on ...............................................13

Figure 1.2.13 Room illuminance when TV is on or off ...............................................................14

Figure 1.2.14 CLASP Room illuminance when TV is on or off on Weekdays ...........................14

Figure 1.2.15 CLASP Room illuminance when TV is on or off on weekends ............................15

Figure 1.2.16 LBL average room illuminance while TV on and off............................................15

Figure 1.2.17 LBL average room illuminance on a weekday while TV on and off.....................16

Figure 1.2.18 LBL average room illuminance on a weekend while TV on and off.....................16

Figure 1.3.1 Ideal TV ABC curves show an “S

- shaped” change in luminance as room

illuminance increases. ............................................................................................18

Figure 1.3.2 Screen luminance and power consumption vs. room illuminance for a TV

with an incremental approach t o ABC. ..................................................................20

Figure 1.3.3 Screen luminance and power consumption vs. room illuminance for a TV

with a single step approach to ABC. ......................................................................21

Figure 1.3.4 Screen luminance and power consumption vs. room illuminance for a TV

that reduces luminance when room illuminance increases beyond 150 lux ..........21

Figure 1.3.5 Power consumption vs. room illuminance for a single manufacturer that

implements ABC as a single step response across six TVs of various sizes

and technologies.....................................................................................................22

Figure 1.3.6 Power consumption vs. room illuminan ce for TV sizes 23” – 42”. ......................23

Figure 1.3.7 Power consumption vs. room illuminance for TV sizes 46” – 47”. ......................24

Figure 1.3.8 Power consumption vs. room illuminance for TV sizes 51 and above. .................25

Figure 1.4.1 Distribution of measurements in CLASP, LBL, and CEA data sets. The

lux values are the mid -points of logarithmic bins. .................................................27

Figure 1.4.2 Power consumption vs. room illuminance at additional test points. All TVs

are 2011 model year. ..............................................................................................28

Figure 1.5.1 Light source directed at the room illuminance meter to confirm

illuminance (left) and placement of the light source over the ALS on the

TV bezel (upper and lower right)...........................................................................313 

### ANALYSIS OF ROOM ILLUMINANCE AND

TELEVISIONS WITH AUT OMATIC BRIGHTNESS CONTROL

1.1 INTRODUCTION

This report provides a comparison of three recent U.S.-based studies on typical room

illuminance levels during television viewing events. The purpose of these investigations was to

det ermine the appropriate room illuminance levels at which to test the effectiveness of automatic

brightness control (ABC), an energy-saving feature increasingly found in new TVs. A TV with

ABC enabled w ill reduce its screen luminance a 

### automatically in response to lower ambient

lighting conditions (termed room illuminance). Currently, ENERGY STAR requires TVs with

ABC to be tested at 0 and 300 lux, and often times the variation in screen luminance occurs in a

single step; therefore TVs viewed at 10 lux could b e at the same brightness as those in a 300 lux

room. A Japanese study b 

### which included room illumanince measurements in Japanese homes

provided some indications that 0 and 300 lux were extreme conditions, though television viewing

preferences may be differe nt in Japan than in the U.S. Anecdotal evidence indicated that 0 lux,

i.e. total darkness, was unusual in the U.S. as well. These studies were initiated in order to obtain

a better understanding of actual room illuminance conditions in the U.S.

The firs t study c 

### was conducted by the Lawrence Berkeley National Laboratory (LBL) in

9 homes, 5 in Colorado and 4 in the San Francisco Bay area of California, during May and June

of 2011. An initial set of one- time room illuminance measurements were taken at 5 points: the

center of the room, the viewing location, the top of the TV cabinet, the center of the TV screen,

and at the location of the ABC sensor d 

### . This was done in order to establish the variance in

illuminance within a TV viewing room. Then a power meter was attached to the TV and an

illuminance meter placed at the center of the bottom bezel of the TV for up to 2 weeks, and a

simultaneous measurement of TV power and room illuminance recorded every 10 minutes in

order to monitor room illuminance during actual TV viewing. Although a useful pilot study, the

measurements were limited by the sample size, length of data collection, time of year (e.g.,

seasonality), geography, and the use of multiple measurers.

a The terms “luminance” and “illuminance” are potentially confusing. Luminance, typically measured in cd/m 2 , is a

measure of light intensity; it is used to measure the amount of light emitted from a source such as a TV screen.

Illuminance, typically measured in lux, is a measure of the intensity of incident light from all directions; it is used to

measure the level of ambient lighting in, e.g., a room.

b Matsumoto et al., 2011, Appropriate Luminance of LCD

- TV Screens under Actual Viewing Conditions at Home,

Journal of the Society for Information Display, Volume 19, Issue 11, pp. 813

- 820

.

c The full report on this study may be found under the current test procedure rulemaking activity at

http://www1.eere.energy.gov/buildings/appliance_standards/ residential/tv_sets.html

. d If the TV was not ABC

- enabled, the measurement was taken from either bottom corner of the TV.4 

### The second study e 

### , by the Consumer Electronics Association (CEA), took measurements

in 234 homes betwe en September and December 2011. Of these measurements, 101 were

collected by a consultant while 133 were collected by volunteers. The measurements were more

geographically diverse, although the majority (62%) were in California. This study only took a

single measurement at the center of the bottom bezel of the TV, asking participants to set up the

room as they would during typical television viewing (i.e., whether the blinds would be drawn

and what artifi cial lights would be on). This study therefore did not capture any variation in room

illuminance while the TV was being viewed at different times of day. Also, due to various

considerations, 35 of the measurements were deemed unreliable by the CEA and excl uded from

the analysis.

The third study f 

### was conducted by the Collaborative Labeling and Standards Program

(CLASP), and took measurements in 60 homes evenly split between Sacramento, California and

Washington, D.C., during October and November 2011. The television -viewing environment

was sketched and photographed to document natural and artificial light sources and other major

physical characteristics. Similar to the LBL study, the five point illuminance measurements were

taken and these were also mapped on to the sketch of the room. The TV was then fitted with an

illuminance meter and a power meter. The illuminance meter was located in the middle of the

bottom bezel of the TV. Data were recorded at 5 -minute intervals for approximately 7 days.

CLASP wo rked with Shugoll Research to select a diverse sample of homes in order to

obtain a broad range of lighting conditions. A screening criterion was used to achieve a

demographic mix of household size, age, gender and income, as well as a variety of housing

t ypes including single -family homes, apartments and row houses. However, the sampling was

still limited geographically and seasonally. Note that CLASP excluded 6 of the households from

the final dataset, due to either faulty metering equipment or the househ old failing to view

television during the data collection period.

In addition, to determine the appropriate room illuminance levels at which TVs with

automatic brightness control should be tested, this report also examines how current TVs respond

to dif ferent lighting levels. Testing the current implementation of ABC by manufacturers

demonstrates both what type of response is technically possible and at what lighting levels TVs

adjust their brightness and therefore their power consumption. Because the ma jority of TV power

is associated with producing light, ABC is a key method used for decreasing reported power.

The re is a close relationship between luminance and power, as shown in more detail in the later

sections of this report. Examining a TV’s luminan ce at various lighting levels can reveal if a TV

is too dim, meaning it is over -utilizing ABC to save power, or too bright, meaning it is underutilizing ABC and missing energy savings opportunities.

Section 1.2 describes th e comparative analysis of the 3 recent room illuminance studies.

Section 1.3 discusses testing performed on televisions with ABC enabled. Section 1.4 provides

some discussion on the results, and Section 1.5 summarizes the main results in this report.

e See comments submitted by the CEA to the Department of Energy, Docket No. EERE

- 2010

- BT

- TP

- 0026.

f The full report on the CLASP stud y is available for download at

http://www.clasponline.org/en/ResourcesTools/Resources/StandardsLabelingResourceLibrary/2 011/Background

Illuminance

- Levels5 

### 1.2 COMPARISION OF ROOM ILLUMINANCE STUDIES

1.2.1 Time of Day

In order to determine the comparability of the three studies it was important to consider

the time of day at which measu rements were recorded, due to the expected influence of bright

sunlight on room illuminance. The distribution of time of day at which measurements were

recorded is illustrated in Figure 1.2.1

, Figure 1.2.2 , and Figure 1.2.3 . As can be seen from these

figures, the majority of viewing events occur in the evening. However, the CLASP data has some

more significant values in the earlier part of the day. Deeper investigation re vealed that this was

specific to measurements recorded in Washington, D.C., as shown in Table 1.2.1 , and does not

appear to be representative of average behavior. Further comparison with the American Time

Use Survey g 

### , which sur veys a representative cross -section of the population, indicates more

significant TV viewing in the evening (see Figure 1.2.4 ). The three studies are therefore

considered reasonably representative.

Figure 1.2.1 Time of day distribution in the CLASP data

g The Bureau of Labor Statistics’ American Time Use Surveys are available to download at http://www.bls.gov/tus/

going back to 2003

. Last accessed 1/30/2012

. 0 10 20 30 40 50 60 70 80 90

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of data points

Hour of day 

# CLASP Time Distribution6 

### Figure 1.2.2 Time of day distribution in the LBL data

Figure 1.2.3 Time of day distribution in the CEA data

Table 1.2.1 Day and night time hours in the CLASP study by location

Daytime Nighttime Total

hours

D.C. 951 615 1566

Sacramento 662 747 1409

Total 1613 1362 2975 0 2 4 6 8 10 12 14 16

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of data points

Hour of day 

# LBL Time Distribution

0 5 10 15 20 25 30 35

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of data points

Hour of day 

# CEA Time Distribution7 

### Figure 1.2.4 Distribution of television viewing times from the

2010 ‘American Time Use Survey’

1.2.2 Range of Illuminance Measurements per Event

A comparison of the range of room illuminance measurements is shown in Figure 1.2.5

below. The x- axis indicates mean room illuminance for each measured viewing event (defined as

a time period during which the TV was continuously on), for the CLASP and LBL studies, and

each single measurement in the CEA study. The y

- axis indicates the cumulative fraction of the

measurements at or below that illuminance level. 0 1000 2000 3000 4000 5000 6000 7000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of data points

Hour of day8 

### Figure 1.2.5 Comparison of room illuminance cumulative

distributions of the 3 sets of data. Data are averaged

over viewing events.

The y -axis is also divided into even quartiles, and Table 1.2.2 shows the mean room

illuminance in the middle of each quartile as well as at each quartile boundary. Interestingly, the

CEA and CLASP results are closely related at lower lux levels, with almost identical

distributions below the median point (50% of cumulative events). Above the median point, the

CLASP and LBL results are more similar.

Table 1.2.2 Mean room illuminance vs. cumulative event fraction

Cumulative events (%)

12.5 25 37.5 50 62.5 75 87.5

Study Room illuminance (lux)

CEA 1.0 5.9 9.7 13.3 20.2 35.6 69.9

CLASP 2.0 5.8 9.9 16.4 27.5 43.4 85.8

LBL 3.9 9.2 12.9 16.9 32.7 50.4 107.8

The CEA study generally found lower lux levels than the other two studies, with 75% of

measurements below 36 lux. The LBL dataset consistently found the highest lux values in all

quartiles, only coming close to the CLASP study at the median point. This result is unusual given

that more daytime viewing events were recorded in the CLASP study; however, some of the

viewing events in this survey were very long, spanning daylight hours into the evening. (For

example, one home in the D.C. area explained that they keep the TV on for most of the day for

background noise, and the lux level in the room varied considerably during that time). Ave raging Lower Quartile

Upper Quartile

Median

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

0 1 10 100 1000 10000Cumulative fraction

Mean room illuminance (lux) CLASP

LBL

CEA

Lower Quartile

Upper Quartile

Median9 

### over individual viewing events may therefore lead to reduced accuracy, but was necessary in

order to directly compare the continuous measurements of the LBL and CLASP studies with the

one- time measurements of the CEA study.

1.2.3 Range of Illuminance M easurements per Hour

Given the above observations, the mean lux per hour (while viewing TV) may be a more

representative measurement than the mean lux per viewing event. The LBL and CLASP data

were therefore reanalyzed using the mean lux per hour, shown in Figure 1.2.6 . The CEA did not

continuously record room illuminance during viewing events; those data are therefore included

on the same one-time measurement basis as above, for comparison.

Figure 1.2.6 Room illuminance per hour of TV viewing

Table 1.2.3 shows the room illuminance measurements in each quartile. The CLASP

study still shows significantly lower lux levels than the LBL study in a given quartile. This may

just be a reflection of the difference in dataset size: only 9 homes were measured for the LBL Lower Quartile Median Upper Quartile

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

0.01 0.1 1 10 100 1000 10000Cumulative viewing hours

Room illuminance (lux) CEA

CLASP

LBL

Lower Quartile

Median

Upper Quartile10 

### survey, and data were only recorded for 7-14 days. A few viewing events in bright conditions

might therefore easily skew the data towards higher values, even though the majority took place

at more com monly-found low lux levels.

Another factor that may explain the difference is seasonality. The LBL survey took place

in late spring when daylight hours are longer and conditions brighter, while the CLASP study

took place in late autumn, when hours of daylight are shorter. Collection of room illuminance

data over a several -month period in the same locations would be helpful to resolve how much

seasonality affects average lux levels.

All 3 datasets indicate that the majority (more than 75%) of viewing occ urs at less than

50 lux, which is much lower than 300 lux, the upper illuminance level currently required by the

ENERGY STAR program. In addition, these studies confirm that while a significant fraction of

viewing occurs in low-lux conditions, 0 lux is ext remely rare. The CLASP study is the most

comprehensive and recorded lux levels to two decimal points, and less than 0.2% of

measurements were at exactly 0 lux

.

Table 1.2.3 Mean room illuminance vs. cumulative viewing hours

Cumulative viewing hours (%)

12.5 25 37.5 50 62.5 75 87.5

Study Room illuminance (lux)

CLASP 0.9 4.5 8.8 15.1 26.4 40.6 87.4

LBL 2 8 12 16 28 49 119.5

1.2.4 Comparison Between Weekday and Weekend

An interesting consideration was how TV viewing habits vary on the weekend compared

to weekdays, and in particular, whether more viewing occurs in daylight hours on the weekend,

and therefore if viewing occurs at higher room illuminance levels. Figure 1.2.7 shows the

number of data points that were recorded separated by weekday and weekend for the CLASP

study. A very clear preference for evening viewing is obvious, and weekday and weekend follow

very similar patterns in relation to the time of day at which the television is viewed.11 

### Figure 1.2.7 CLASP study data points by type of da y

In order to determine whether there was a preference for watching TV during the daytime

on the weekend, the two subsets of data were normalized to a single day, by dividing the

weekday data by 5 and the weekend data by 2. The result, shown in Figure 1.2.8 , indicates that

viewing is greater on weekends between 9 am and 5 pm, but that viewing is greater on weekdays

at all other times. Overall, total weekend viewing time is equivalent to an average of 7.1 hours

per household, only slightly greater than the total weekday viewing time of 6.8 hours. These

viewing hours are close to those for a primary TV as derived from Nielsen metered viewing data

for an average U.S. household in 2010. h



### Figure 1.2.8 Normalized CLASP study data points by type of day

The LBL data are shown in Figure 1.2.9 , and also demonstrate more viewing during the

evening than the day. The data normalized to a single day are shown in Figure 1.2.10 . The

daytime w eekend peak is more pronounced, especially from 11am to 4pm. Overall, total

weekend viewing time is equivalent to 3.6 hours per household, while weekday viewing time is

h Average monthly viewing time (in minutes) from up to 21,000 households was collected by The Nielsen Company

from May 2007 to May 2011. The last full calendar year available (2010) was used in comparing to the room

illuminance data presented here. 0 500 1000 1500 2000 2500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of data points

Hour of the day 

# CLASP

Weekday

Weekend

0 50 100 150 200 250 300 350 400 450

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Normalized number of datapoints

Hour of day 

# Normalized CLASP Data

Weekday

Weekend day12 

### equivalent to 2.6 hours per household. The overall viewing hours here are much lower than those

derived in the CLASP study, and the national average derived from the Nielsen data. It is

important to note, however, that only 9 homes participated in the LBL study, and as such there

was less significant variation in demographics.

Figure 1.2.9 LBL data points by type of day

Figure 1.2.10 Normalized LBL data points by type of day

Figure 1.2.11 and Figure 1.2.12 show the average room illuminance by time of day while

the TV was on, separated by weekday and w eekend. The CLASP data show a clear relationship

between lux and time of day, peaking at approximately midday and being darkest before 6 am

and after 6 pm. At 6 am and 8 am on the weekend, however, there are spikes in lux levels that are

not evident elsewhere in the distribution. The cause of these spikes is unknown at this time. 0 20 40 60 80 100 120

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of data points

Time of day 

# LBL

Weekday

Weekend

0 5 10 15 20 25 30 35

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Normalized number of data points

Time of day 

# Normalized LBL

Weekday

Weekend13 

### Figure 1.2.11 CLASP lux by time and type of day when TV was on

The LBL study exhibits a clear decrease in lux from 3 pm onward during the week, and

from 4 pm onward on the weekend. There is significant variability in the distribution, however,

due to the fewer number of data points recorded at other times.

Figure 1.2.12 LBL lux by time and type of day when TV was on

Comparing the two figures, the LBL study shows higher lux levels than the CLASP

st udy. It is difficult, however, to draw any significant conclusions from this due to the small

number of homes that were measured in the LBL study. The most important thing to note is that

the majority of viewing, consistently across all three major studies , whether per event or per

hour, occurs at room illuminance levels of 50 lux or less.

1.2.5 Room Illuminance with the TV On or Off

Another interesting consideration is whether people typically alter room illuminance

conditions in order to watch TV (e.g., using blinds or artificial lighting). To provide an indication

of this, the illuminance values measured by CLASP were divided into TV-on or TV-off and are

presented in Figure 1.2.13 . In general, the room illuminance is higher while the TV is on, 0 50 100 150 200 250

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Average illuminance (lux)

Time of day 

# CLASP

Weekday

Weekend

0 100 200 300 400 500 600

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Average room illuminance (lux)

Time of day 

# LBL

Weekday

Weekend14 

### indicating the probable use of artificial lighting, with the exception of the hours from 8 am to

noon. The difference between the illuminance with the TV-on or TV-off is most pronounced for

the hours of 8 am to 10 am, indicating the possible use of window shades during TV viewing at

this time of day. The exact cause of this significant change in room illuminance is not known at

this time, but may be a result of the majority of rooms having east

- facing windows.

Figure 1.2.13 Room illuminance when TV is on or off

The data were further divided into weekday and weekend day, to see if this affected the

room illuminance while the TV was on or off. Figure 1.2.14 shows the weekday results, and it

can be seen that room illuminance is higher while the TV is on with the exception of 8 to 10 am,

similar to above. Figure 1.2.15 shows the weekend day results. In this case, the room illuminance

is higher with the TV on from 9 am to about 4 pm, indicating the probable use of window shades

during daytime viewing.

Figure 1.2.14 CLASP Room illuminance when TV is on or off on

Weekdays 0 50 100 150 200 250 300 350 400 450 500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Mean room illuminance (lux)

Hour of day 

# CLASP Total viewing times

TV off

TV on

0 100 200 300 400 500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Mean room illuminance (lux)

Hour of day 

# CLASP Weekday Viewing

TV off

TV on15 

### Figure 1.2.15 CLASP Room illuminance when TV is on or off on

weekends

The LBL data were also divided into TV on or off subsets, as shown in Figure 1.2.16

. The data are more scattered than the CLASP data due to the smaller number of households

sampled. The distributions suggest the probable use of artificial lighting in the evening and early

morning, and lower room illuminance during the day likely indicates the probable use of window

shades while watching TV. While there are generally lower room illuminance levels during the

day, however, indicating the probable use of window shades, there are other periods (e.g.,

between 2 p m and 7 pm) that do not seem to follow any easily-explained pattern.

Figure 1.2.16 LBL average room illuminance while TV on and off

The data were also separated into weekday and weekend as shown in Figure 1.2.17 and

Figure 1.2.18 respectively. The TV -off curves clearly follow daylight hours. The pattern is,

however, is less smooth during the weekday, indicating the possible use of window shades

during the day.

The weekday TV -on room illuminance is bright er than the TV -off in the early morning

and late evening, indicating the probable use of artificial lighting at these times, while between 9 0 100 200 300 400 500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Mean room illuminance (lux)

Hour of day 

# CLASP Weekend Viewing

TV off

TV on

0 50 100 150 200 250 300 350 400 450 500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Average illuminance (lux)

Hour of day 

# LBL Total

TV off

TV on16 

### am and 7 pm the reverse is true, indicating the possible use of window shades during viewing at

these times.

Figure 1.2.17 LBL average room illuminance on a weekday while

TV on and off

The weekend TV -on room illuminance is lower than the TV-off during the morning from

8 am to 2pm, and then the reverse is true for the rest of the day. This indicates the probable use

of window shades during morning viewing, and artificial lighting the rest of the day. The very

high room illuminance during TV viewing at 3 pm and 4 pm is likely due to the small dataset

and the result of a single viewing session.

Figure 1.2.18 L BL average room illuminance o n a weekend while

TV on and off

In general, all of these results indicate that many people adjust lighting levels while

watching TV (both up and down), although there is no way of knowing whether the room was

used for other activities when the TV was off , or was empty with room illumance levels simply

depending on the time of day. 0 100 200 300 400 500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Average illuminance (lux)

Hour of day 

# LBL Weekday

TV off

TV on

0 100 200 300 400 500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Average illuminance (lux)

Hour of day 

# LBL Weekend

TV off

TV on17 

### One last consideration is whether, when the TV is on, the room illuminance can actually

be 0, given that the TV itself generates light which is reflected off surfaces and wa lls back to the

ABC sensor. The LBL study used meters that recorded integer lux values, which are not precise

enough to answer this question. The CLASP study recorded lux levels to 2 decimal places (with

tolerances on the accuracy of the meter). Of the 348 27 measurements with the TV on, only 58

are recorded as 0. This is less than 0.2% of the measurements. This suggests that 0 lux levels,

while possible, are highly unlikely in actual TV- viewing conditions.

1.3 TESTING TELEVISIONS WITH ABC

1.3.1 Ideal Behavior

The h uman eye perceives light logarithmically. That is, it perceives every doubling of

brightness as a subjectively similar degree of increase in lighting levels. Therefore, an increase

from 10 to 20 lux seems the same as an increase from 100 to 200 lux, for ex ample. As the light

levels increase, it takes more and more of an increase for the human eye to notice. For TVs, this

means that ABC needs to be more responsive to room lighting at lower levels to maintain the

contrast between the room illuminance and the TV brightness for our eyes to more comfortably

watch TV. Figure 1.3.1 shows this ideal relationship. Generally speaking, TVs with ABC

responses close to this pattern (example also included in Figure 1.3.1 ) are more comfortable to

watch than ones which maintain the same luminance at lower room illuminance levels. It has

been shown in the previous section that most TV viewing occurs at these lower illuminance

levels. The ideal TV luminance levels for d ark room conditions in Figure 1.3.1 are based on

Imaging Science Foundation’s (ISF) recommended brightness level for TVs in a dark room

setting i 

### , while the luminance levels for brighter conditions are based on a 2010 study j 

### on appropriate luminance levels , which found that at 100 lux, subjects preferred a TV brightness

range from 160 to 248 cd/m 2



### .

i Personal communication, Joel S ilver, Imaging Science Foundation, March 17, 2010

. j Matsumoto et al., 2011, Appropriate Luminance of LCD

- TV Screens under Actual Viewing Conditions at Home,

Journal of the Society for Information Display, Volume 19, Issue 11, pp. 813

- 820

.18 

### Figure 1.3.1 Ideal TV ABC curves show an “S

- shaped” change in

luminance as room illuminance increases.

1.3.2 Testing Results

DOE, ENERGY STAR , and CLASP k 

### have conducted TV luminance and power testing at

various lighting levels between 0 and 300 lux ( Table 1.3.1 ). All power measurements were taken

using the 10 minute IEC video test clip referenced in IEC 62087. DOE and ENE RGY STAR

luminance measurements were conducted using the 3

- Bar test pattern specified in ENERGY

STAR’s current (5.3) test method. Luminance measurements for TVs tested by CLASP were

made using the 9-Point test pattern (highlighted in green in Table 1.3.1 ).

For 8 of the 21 DOE TVs, no luminance measurements were taken and power

measurements at 30 and 50 lux were not taken ( see Table 1.3.1 ). CLASP TVs were measured at

10, 50, 150 and 300 lux only for both power and luminance. Because of the incomplete (and

varied) luminance measurements and methodologies, this report concentrates on power

measurements, though as shown below, there is a clear relationship between television

luminance and power. In the figures below, dotted lines are used to connect measurement points,

k The full CLASP report is available for download at:

http://www.clasponline.org/en/ResourcesTools/Resources/Standar dsLabelingResourceLibrary/2011/Analysis

- of

- tv

luminance

- and

- power

- consumption19 

### but are not meant to represent any interpolation. No assumptions are made about the ABC

response in between measurement points.

Table 1.3.1 Summary table of DOE, ENERGY STAR and CLASP TV power and

lu mi nance testing. No color: Power measured at 0, 10, 100, 150, and 300

lux , no luminance measurements ; Blue: Power and luminance measured

at 0, 10, 30, 50, 100, 150, and 300 lux ; Green: Power and luminance

measured at 10, 50, 150 and 300 lux.

ID Year Size /Tech Power (W) Luminance (cd/m2)

0

lux 10

lux 30

lux 50

lux 100

lux 150

lux 300

lux 0

lux 10

lux 30

lux 50

lux 100

lux 150

lux 300

lux

DOE 1 2010 23" LED 19 19

- - 27 27 27

- - - - - - -

DOE 2 2010 32" LED 42 83 84 84 83 83 83 41 297 296 296 297 298 299

DOE 3 2010 32" LED 29 29 30 39 43 43 47 128 128 142 203 238 247 259

DOE 4 2010 40" LED 59 113

- - 113 113 113

- - - - - - -

DOE 5 2010 42" LED 62 63 63 74 87 91 90 94 98 130 159 231 248 234

DOE 6 2010 42" LED 46 56

- - 101 101 101

- - - - - - -

DOE 7 2010 46" CCFL 104 104 108 110 130 130 130 232 234 241 247 283 300 299

DOE 8 2010 46" LED 28 66 66 66 66 66 66 29 236 236 236 236 236 236

DOE 9 2011 46" LED 44 46 54 62 76 86 86 73 72 88 113 221 316 364

DOE 10 2010 46" CCFL 65 70

- - 126 124 12 4

- - - - - - -

DOE 11 2011 47" LED 37 79 79 80 80 79 79 18 286 282 283 285 284 284

DOE 12 2010 47" LED 71 74

- - 113 126 126

- - - - - - -

DOE 13 2010 52" CCFL 115 116 122 137 166 166 166 165 169 187 227 301 301 302

DOE 14 2010 52" LED 71 92 93 93 92 120 128 93 267 266 266 267 267 267

DOE 15 2010 54" Plasma 111 198 199 200 199 199 188 23 79 80 80 79 79 79

DOE 16 2011 55" Plasma 89 144 137 144 137 142 138 27 64 64 63 64 63 63

DOE 17 2010 55" LED 59 60 78 86 98 98 98 92 92 152 188 236 236 237

DOE 18 2010 55" LED 71 121

- - 151 151 151

- - - - - - -

DOE 19 2010 60" Plasma 246 435 433 433 435 434 435 68 75 80 81 80 80 80

DOE 20 2010 60" LED 60 61

- - 91 106 113

- - - - - - -

DOE 21 2010 63" Plasma 163 246

- - 246 247 247

- - - - - - -

ES 1 2011 46" LED 1 61 81 82 81 82 82 82 158 278 278 278 278 278 277

ES 2 2011 60" LED 49 116 116 116 116 116 116 116 407 408 407 407 408 409

ES 3 2011 46" LED 2 55 60 76 83 95 95 55 95 155 233 269 302 302 94

ES 4 2011 51" Plasma 85 123 123 123 123 124 123 38 63 6 3 63 63 63 63

CLASP 1 2010 42" Plasma

- 48

- 63

- 86 102

- 29

- 42

- 111 172

CLASP 2 2010 42" Plasma

- 112

- 122

- 122 122

- 78

- 79

- 79 79

CLASP 3 2010 46" LED

- 67

- 82

- 83 83

- 194

- 275

- 278 279

CLASP 4 2010 40" LED

- 88

- 109

- 123 123

- 126

- 177

- 202 205

CLASP 5 2010 55" LED

- 81

- 164

- 165 165

- 49

- 426

- 427 427

CLASP 6 2010 42" LED

- 52

- 54

- 113 114

- 38

- 44

- 326 326

CLASP 7 2010 37" LED

- 43

- 47

- 110 110

- 56

- 122

- 528 528

CLASP 8 2010 40" LED

- 38

- 47

- 61 61

- 68

- 130

- 207 208

CLASP 9 2010 40" LED

- 51

- 67

- 87 88

- 92

- 143

- 277 278

CLASP 10 2010 52" LED

- 47

- 56

- 84 84

- 82

- 123

- 217 218

CLASP 11 2010 32" LED

- 45

- 46

- 46 46

- 120

- 120

- 121 194



### Upon reviewing testing completed by DOE, ENERGY STAR and CLASP, several

patterns emerge. First, there are two ways in which TVs respond to a range of room iluminances

– with a gradual or incremental increase in luminance and power as the room brightness

increases ( Figure 1.3.2 ), or in a single step from low to high brightness ( Figure 1.3.3 ). This20 

### second response largely negates the viewing benefits of ABC by operating at a fixed screen

luminance under most ambient light conditions. Because the current ENE RGY STAR eligibility

criteria (v5.3) uses the weighted average of measured TV power consumption at 0 lux (45%) and

300 lux (55%) room illuminance with ABC enabled, the single step response results in an

unrealistically low value for average TV power consumption. A variation on these response

patterns is found in Figure 1.3.4 . Here, a TV reduced its brightness at some point after the room

illuminance reached 150 lux.

Figure 1.3.2 Screen luminance and power consumption vs. room

illuminanc e for a TV with an incremental approach

to ABC. 0 50 100 150 200 250 300 350 400

0 20 40 60 80 100

0 50 100 150 200 250 300 350Luminance (cd/m2)Power (W)

Room Illuminance (lux)

0 50 100 150 200 250 300

0 10 20 30 40 50 60 70 80 90

0 50 100 150 200 250 300Luminance (cd/m2)Power (W)

Room Illuminance (lux)21 

### Figure 1.3.3 S creen luminance and power consumption vs. room

illuminance for a TV with a single step approach to

ABC.

Figure 1.3.4 Screen luminance and power consumption vs. room

illuminance for a TV that reduces luminance whe n

room illuminance increases beyond 150 lux

Another pattern that emerges is that TV manufacturers tend to implement ABC in the

same fashion across different technologies and sizes , at a given point in time ( Figure 1.3.5 ).

The re were two exceptions to this pattern. One manufacturer moved from an incremental

approach to a single step approach in its single 2011 model represented in this dataset. The other

was a difference in a manufacturer’s approach to ABC from single step to i ncremental in two

TVs from the CLASP (non- US) TV dataset. 0 50 100 150 200 250 300 350

0 20 40 60 80 100 120

0 50 100 150 200 250 300Luminance (cd/m2)Power (W)

Room Illuminance (lux)22 

### Figure 1.3.5 Power consumption vs. room illuminance for a

single manufacturer that implements ABC as a

single step response across six TVs of various sizes

and technologies.

Fig ure 1.3.6 to Figure 1.3.8 show the relationship between power and room illuminance

for all TVs tested. Recall that some DOE TVs were not tested at 30 and 50 lux. Televisions in

the CLASP study were measured at 10, 50, 150, and 300 lux. Power levels were not assumed at 0

lux for the CLASP data.23 

### Figure 1.3.6 Power consumption vs. room illuminance for TV

sizes 23” – 42”.24 

### Figure 1.3.7 Power consumption vs. room illuminance for TV

sizes 46” – 47”.25 

### Figure 1.3.8 Power consumption vs. room illuminance for TV

si zes 51 and above.26 

### 1.4 DISCUSSION

Tracking the impact of ABC on a range of different TV technologies and sizes is difficult

because of their inherent efficiency differences. Nevertheless, there are a few general

conclusions.

A gradual (non- single

- step) ABC response curve has the potential to save a significant

amount of power relative to a single- step implementation. For all TVs measured at 0 lux, there

are considerable savings. However, from the earlier discussion of reported room illuminances,

this was fo und to be an unlikely condition while TV was being viewed. Power savings are also

evident at 10 and 30 lux. To a lesser extent, savings occur at 100 lux as several of the TVs

measured did not achieve maximum power until the room lighting was increased further.

Significantly, these TVs exhibit the more ideal “s

- shaped” response function, with respect to

power and room illuminance. Finally, the testing revealed that not all TVs reach maximum

luminance at 100 lux.

Some stakeholders have commented publicly that, while more lux levels should be

incorporated in the testing of ABC (e.g., 10 lux), the current requirements of 0 and 300 lux

should be maintained. l 

### There is a buildup of historical data that can be used for comparisons of

future developments of the technology. Stakeholders have further argued that 0 lux provides a

lower limit of the ABC and is easy to measure, minimizing testing burden, while for an upper

limit, the ABC is likely to saturate at around 100 to 150 lux, so it would not matter which value

is measured beyond this. Some stakeholders therefore recommend that the test should stay at 300

lux. As was shown above, however, 100 lux does not necessarily represent maximum luminance.

Some stakeholders have further suggested that 12 lux and 35 lux b e added as two interim

data points based on the results of the CEA study. The motivation for these illuminance values

can be seen in Figure 1.4.1 , which shows distribution s of the data from all three studies using

logarithmic b ins, rather than the cumulative fraction as is done in this report. Logarithmic bins

were chosen since the human eye perceives light on a logarithmic scale. The distribution shows a

peak at approximately 12 lux (though 12 lux is a midpoint of a logarithmic bin), and 35 lux is

simply the approximate logarithmic mean between 12 and 100 lux (the value at which the ABC

sensor is assumed to saturate according to some stakeholders ). The distributions are roughly

consistent across all three studies.

l See stakeholder comments for Draft 1 Version 6.0 ENERGY STAR Televisions Specification.

http://www.energystar.gov/index.cfm?c=revisions.television_spec27 

### Figure 1.4.1 Distri bution of measurements in CLASP, LBL , and

CEA data sets . The lux values are the mid -points of

logarithmic bins.

The CLASP report, on the other hand, states that only 0 and 300 lux should not be used.

Their findings indicated insignificant TV viewing occurred in 0 lux conditions, and that the vast

majority was below 100 lux. CLASP tested televisions for both power and luminance at 10, 50,

150, and 300 lux. They also emphasize the importance of requiring more than 2 measurement

points, in order to ensure ABC o perates as a gradual change in TV luminance with changing

room illuminance, avoiding a step profile. They also state, however, that due to the geographical

limitations of their study, further analysis would be necessary before making a final decision

regar ding appropriate illuminance levels. The ir preliminary recommendation was to test at 3

points between 10 and 100 lux.

According to the CLASP and LBL room illuminance studies, which gathered continuous

measurements during actual TV viewing, room illuminan ce values are approximately

1/5/10/15/30/45/100 lux at the 12 th 

### /25 th 

### /37 th 

### /50 th 

### /62 nd 

### /75 th 

### /87 th 

### percentiles. One possible set of

testing levels could therefore be 5/15/45/135, based on the 25 th 

### , 50 th 

### , and 75 th 

### percentiles (plus an

additional point to represe nt maximum luminance). Another possible set of testing levels could

be 1/10/30/100/300, based on the 12 th 

### , 37 th 

### , 62 nd 

### , and 87 th 

### percentiles (plus an additional point to

represent maximum luminance).

DOE performed some additional testing to determine t he significance of adopting any of

the above illuminance level recommendations . The additional testing was performed on the

seven 2011 model year TVs in the sample, to represent the latest ABC implementations. The se

test results are shown in Figure 1.4.2 and summarized in Table 1.4.1 below. Table 1.4.2 shows

the percent change in power calculation methods from the ENERGY STAR methodology

(except for ENERGY STAR, all room illuminance points are weighted equally). For the one TV

that implements a gradual and monotonically increasing ABC response curve, all of the proposed

ABC calculations result in a more favorable reported energy consumption valu e compared to the - 5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0

0.5 1.5 3 6 12 24 48 96 192 384 768 1536number of records

Room Illuminance (lux) CLASP

LBL

CEA28 

### other TVs, relative to the existing ENERGY STAR calculation. This is incentivizing the correct

ABC behavior.

Figure 1.4.2 Power consumption vs. room illuminance at

additional test points. All TVs are 2011 model year.

Table 1.4.1 Power measured at additional room illuminance levels between 0 -300 lux

for seven 2011 TV models.

46" LED

(DOE) 47" LED

(DOE) 55" Plasma

(DOE) 46" LED 1

(EPA) 60" LED

(EPA) 46" LED 2

(EPA) 51" Plasma

(EPA)

Power @ 1 lux (W) 43.9 79.2 89.8 76.0 48.9 54.5 85.3

Power @ 5 lux (W) 43.9 79.3 137.3 81.3 77.1 54.6 10 4.2

Power @ 10 lux (W) 45.5 79.4 143.5 81.3 115.7 59.7 123.2

Power @ 12 lux (W) 47.2 79.5 137.2 81.4 115.9 61.6 123.5

Power @ 15 lux (W) 48.9 79.4 137.2 81.3 115.9 62.2 123.1

Power @ 30 lux (W) 53.8 79.3 137.0 81.5 115.9 75.6 123.4

Power @ 35 lux (W) 55.4 79.5 141.1 81.3 115.8 76.8 123.8

Power @ 45 lux (W) 60.2 79.4 136.6 81.3 115.9 80.8 123.5

Power @ 50 lux (W) 61.8 79.5 143.7 81.4 115.9 82.7 123.1

Power @ 100 lux (W) 75.6 79.5 137.3 81.6 115.8 94.9 123.4

Power @ 135 lux (W) 85.9 79.7 133.2 81.6 1 16.1 95.2 123.2

Power @ 150 lux (W) 85.8 79.4 142.2 81.7 116.0 95.3 123.7

Power @ 300 lux (W) 85.8 79.3 137.7 81.7 116.0 54.6 122.829 

### Table 1.4.2 Percent change in power calculation methods from ENERGY STAR

methodology.

Power Calculation Method 46" LED

(DOE) 47" LE D

(DOE) 55" Plasma

(DOE) 46" LED

1 (EPA) 60" LED

(EPA) 46" LED

2 (EPA) 51" Plasma

(EPA)

ENERGY STAR

- - - - - - -

10, 50, 100, 300 0% 31% 21% 13% 35% 34% 16%

0, 12, 35, 300

- 13% 14% 9% 5% 16% 13% 7%

0,10,300

- 13% 8% 6% 3% 9% 3% 4%

5, 15, 45, 135

- 11% 32% 17% 12% 24% 34% 12%

1, 10, 30, 100, 300

- 9% 31% 11% 11% 19% 24% 9%



### Comparing with the other two room illuminance studies, the CEA data measured

consistently lower lux values. This may be a result of seasonality effects, or due to the nature of

the one-time measurement, as opposed to continuously monitoring during actual television

viewing. Concerns raised by other studies include setting a tolerance for each illuminance level;

specifying the light source during the test; and the angle at which light enters the sensor.

Currently the ENERGY STAR measurement is described as “directly into the sensor.”

Another important consideration raised by CLASP was that further studies were needed

in countries outside the U.S. Some studies have been carried out to date in Japan and Korea, and

it has been found that they tend to have much higher room illuminance levels than those found in

the U.S.

1.5 SUMMARY

The main purpose of this analysis is to help illuminate discussions on appropriate room

illuminance levels at which TVs with automatic brightness control should be tested. The current

ENERGY STAR test procedure requires TVs to be tested at 0 and 300 lux. The data presented

here indicate that these values are extreme compared to illuminance levels generally measure d

while watching TV. Less than 0.2% of measurements in the CLASP study are at exactly 0 lux,

and in all 3 studies, only a few percent of measurements are at 300 lux or greater. Testing at 0

lux allows for potentially artificial behavior during testing (wit h very low luminance), behavior

that was confirmed in recent testing. The current test requirements also allow manufacturers to

adjust the TV brightness in a single step to receive the ENERGY STAR endorsement label. ABC

measurements should occur at several room illuminance levels that are representative of actual

TV viewing habits

. In summary :

• The 0 lux level does not represent a typical room illuminance level. It occurs less than

0.2% of the time in the CLASP data.

• The 300 lux level (or greater) is an extreme conditioning occurring less than 5% of the

time.30 

### • The peak of the room illuminance distribution is between 10-15 lux, according to all

three studies. A significant fraction of TV viewing occurs at levels below 10 lux,

however, with a secondary peak at very low (but non-zero) lux values.

• According to the CLASP and LBL studies, which gathered continuous room illuminance

measurements during actual TV viewing, room illuminance values are approximately

1/5/10/15/30/45/100 lux at the 12 th 

### /25 th 

### /37 th 

### /50 th 

### /62 nd 

### /75 th 

### /87 th 

### percentiles. See Table

1.2.3 for more details.

• TV luminance is not necessarily maximized at 100 lux, and the ABC sensor is not

necessarily saturated. Maximum luminance is reliably achieved at 300 l ux, however.

• When implemented in an ideal “S” shape, ABC response has the potential to save a

significant amount of TV energy. When implemented in a step or staircase fashion, the

energy -saving benefits of ABC are reduced.

• For TVs that implement a gradual and monotonically increasing ABC response curve, all

the various proposals for revised room illuminance levels during ABC testing result in a

more favorable reported energy consumption value , as compared to TVs with a step

- wise

response curve.

• Further ro om illuminance testing is recommended to increase the current sample size. In

particular, future studies need to span a representative range of dates during the year, as

well as geography. As was shown here, seasonal effects do have an impact on average

ro om illuminance levels, as does the geographic location. The current studies completed

to date have been largely restricted to only a few cities.

• Future testing should ensure that weekdays and weekends are properly sampled (and the

data normalized) to ensu re final results are representative of a typical week. Initial results

suggest an important difference in weekday and weekend viewing conditions.

• Finally, the results presented here are applicable to the U.S. only. Preliminary studies in

other countries suggest that preferred room illuminance conditions vary from country to

country.31 

### APPENDIX: LATEST TES TING METHODOLOGY

The following test setup was used for the latest DOE measurements, in an effort to

address some potential issues, and create a repeat able and representative methodology.

To control the amount of room illuminance entering the TV’s sensor in a more

reproducible manner, DOE used a dimmable halogen incandescent lamp equipped with a hood

and short tube to direct light onto the ambient ligh t sensor (ALS) ( Figure 1.5.1 ). Before each test,

the lamp output was adjusted until a room illuminance meter measured the desired level of

illuminance ( Figure 1.5.1 , left). The lamp was then placed directly against the ALS on the TV

under test, making certain the lamp hood sat flush with the TV bezel ( Figure 1.5.1 , upper and

lower right). This ensured that the light source was the same distance and orientation in relation

to the illuminance meter as it was in relation to the TV’s sensor. Additionally, the light source

was plugged into a regulated power source to eliminate any drifting of lamp output, which was

noted in earlier testing and resulted in variations in illumina nce measurements of up to 10%. A

diffusing plate was also used inside the hood housing, in between the lamp and the short tube.

Without the diffuser, the ALS was very sensitive to the exact alignment of the lamp, making the

testing difficult to reproduce.

Figure 1.5.1 Light source directed at the room illuminance meter

to confirm illuminance (left) and placement of the

light source over the ALS on the TV bezel (upper

and lower right).