A scientific study on the effects of Ambilight in flat-panel displays

Prof. Dr. Ir. S.H.A. Begemann , Technische Universiteit Eindhoven ( Tue), Netherlands - July 22, 2005


Summary
Based on internal tests Philips has formulated and communicated claims about positive effects of Ambilight. The TUe has been requested to scientifically validate these claims. The experiments conducted by the TUe in a tightly controlled environment with a low overall room lighting level, using balanced assessment methodologies, show the following results:

In a (dark) home cinema room lighting condition (7 lux room lighting level) Ambilight can reduce eye strain in 60-90% of the people dependent on the Ambilight setting and the nature of the film/programme. Ambilight, in particular the active Ambilight- relaxed mode can improve the overall viewing experience, the degree of which depends on the nature of the programme. The active Ambilight – relaxed setting also gives the possibility to add a new overall positive psycho-fysiological experience to certain types of film/ programmes.

1. Introduction
Philips Consumer Electronics (Philips) has conducted internal “viewing” tests with test persons in Germany, Belgium, USA and China using a flat TV 42PF9986 equipped with an Ambilight system.

Test protocol and questionnaires used in the Hamburg and Brugge experiments were made available to the Technical University Eindhoven (TUe) research team as well as the test results. Furthermore Philips indicated that similar tests were conducted in the USA and China. Based on these tests Philips has formulated (and communicated) the following claims about Ambilight:

  1. Viewing with Ambilight is experienced by most viewers as more pleasant and comfortable for the eyes than without it
  2. Ambilight is more relaxing for the eyes (and less tiring for the body)

Philips approached the TUe (Chair: Lighting Science, Engineering and Design of Prof. Dr. Ir. Begemann, Faculty of Architecture) via the Stichting Onderzoek Licht en Gezondheid (SOLG) to conduct a scientific study to verify the claims. Prof. Begemann has both the facilities and measuring techniques/tools to conduct vision- and visual – assessment studies in addition to know-how and equipment to measure bio- physical as well as psychological parameters. The TUe used the test facilities and test protocols* adapted to the specific requirements for the Ambilight research.

* Test protocols developed by TUe can not be used by Philips, WMC or other parties without written permission from Tue

2 Test facilities and –protocols
All viewing experiments with test persons were conducted in a test room measuring 3.6 * 4.8 m with simple furnishing (figure 1). The distance wall - Ambilight strip was 15 cm, which resulted in a relatively large ‘light footprint’ on the wall.

Figure 1, the test room (dimensions in mm)

With this set-up a “neutral” living room condition with representative viewing distance was created. Walls and ceiling were soft white, carpeting was even blue/grey to avoid any “visual distraction“. The test person sat on a comfortable couch in front of the TV, while the researcher sat next to this couch at a small desk with a laptop.

With a dimmable halogen up lighter the overall room lighting level could be set from 0- 200 lux.

The TV set used was a regular Philips 42PF9986. The only modification made at the explicit request of the TUe was in the Ambilight remote control system so that it was possible to remotely change Ambilight settings without onscreen display of the different Ambilight settings and the chosen setting.

In the internal Philips experiments this was not done so that all test persons were influenced by seeing this info (further reducing the scientific value of their judgement).

To scientifically validate the Ambilight viewing effects/experience, stills as well as film scenes were used. They have been selected to enable the best possible detection of an effect. Still pictures by their nature/composition can enhance “focussing” the eyes on a specific area (pictures 1-5 , see below) or the extreme opposite, “scanning“ the whole screen because of the abundance/diversity of visual information

Three different film scenes were used to assess the effects of Ambilight on dynamic viewing experience and eye strain (see below).

Picture 1, red flower

Picture 2, American football

Picture 3, yellow flower

Picture 4, feathers

Picture 5, toy shop

Overall room lighting level
The experiments were conducted at 7 lux ambient lighting level. This is not representative for a normally lit living room but represents a “home cinema” lighting environment that will optimise the experience of Ambilight effects.

Eye tests
Prior to an assessment session the test person was subjected in the test room to a visual acuity test (Landolt-C) and a colour vision test (The Richmond HRR Pseudoisochromatic Plates) to determine the test person’s vision.

Still picture assessment protoco
The following pictures were selected and presented for visual evaluation in the sequence indicated:

  1. Red flower; with Ambilight settings: relaxed/ red
  2. Football; with Ambilight settings: relaxed/warm white/ blue
  3. Yellow flower; with Ambilight settings: relaxed /warm white / blue
  4. Toyshop; with Ambilight settings; relaxed /warm white /blue / red

The picture was shown for 10 seconds under an Ambilight setting. Then Ambilight was turned off for 10 seconds. Then Ambilight was turned on again and a series of questions were asked. Setting was changed to the next condition. After 5 seconds a series of questions were asked about brightness of the TV picture, luminance ratio TV picture – (Ambilight) background and viewing experience. If the test person requested, Ambilight was switched off and on in order to better answer the questions. The questions for one setting took approximately 2.5 min.

Video (moving pictures) assessment protocol Three different kinds of video scenes were used for the assessment of Ambilight effects on dynamically changing visual information.

  1. Part of a soccer match representative for action in/against a relatively constant background with the need to follow small details (ball, players).
  2. Part of a “nature” film which represents a relatively slow changing visual environment that “pleases” the eye
  3. .
  4. Part of a thriller film with fast changing, dramatic scenes with lots of different actions and varying backgrounds requiring a high degree of visual - alertness, -adaptation and -scanning. The different scenes shown had relatively large variations in brightness.

They were shown in the following sequence with Ambilight settings relaxed and warm white:

Sport (1:53 min): - relaxed, off and relaxed - warm white, off and warm white
Nature (1:14 min): - relaxed, off and relaxed - warm white, off and white
Action (2:15 min): - relaxed, off and relaxed - warm white, off and warm white

Participants were asked to answer questions about, luminance ratio TV picture- background, viewing experience and preference for a specific Ambilight setting. To determine if Ambilight had a relaxing effect on the eye and may be overall (on the body) as well, subjective assessment was used. A typical example of such a question is shown in Table 1 below.

Using a Dutch version of the Thayer [Thayer, 1988]Activation - Deactivation Adjective Checklist developed by Kerkhof [Kerkhof, 1988] to “measure” the psychofysiological factors tension and relaxation, an attempt was made to find out whether Ambilight had any noticeable short term non-visual relaxing effects.

Beoordeling helderheidverhoudingen tussen tv-beeld en omgeving

Table 1: example of a 5-point balanced scoring question (original Dutch version, translation see 6 )

Most subjective questions were based on a balanced 3 or 5 point scoring system with a neutral center (representing no change/don’t know etc) and equal positive and negative scoring opportunities. (see e.g. table 1). A few “exploring” questions were used for typical personal experience effects (see e.g. fig.1)

Selection of test persons and test procedure Within the short time period available in the vacation period (July 12th - August 6th, 2004) 87 persons (2/3 male, 1/3 female) were recruited for the test sessions. Age ranged from 22 years to 81 year, with an average of 43 years for males and 42, 5 years for females. As an incentive all test persons would enter a lottery for a Philips 32 inch Flat TV.

One researcher did the tests with 72 persons. During her vacation a second researcher did 15 persons. All answers and remarks during the tests were directly stored in a laptop by the researcher. From the eye tests at the beginning of the test session it appeared that 6 persons had a mild-serious colour defect. They were not eliminated beforehand but completed the whole test session. Their results did not differ in a statistically significant way from the other participants. A total of 46 Persons were shown a still-film order and 41 persons a film-still order. The results of these two groups show no significant difference also.

3. Results
(Graphic representation of examples of typical results shown in fig. 2-4 are given in the original Dutch version to avoid loss of information in translation. Translation is given in 6.)

3.1 General
The answers to all questions of the research protocol of all 87 test persons (total 31407 data points) were statistically analysed using SPSS 12.0.1 (Statistical Package for the Social Sciences) and MS Excel.

Eye tests
Visual acuity test results identified 2 males and 2 females with a score < 0.80="" (considered="" the="" lower="" limit="" for="" seeing="" sufficient="" detail).="" all="" others="" scored=""> 0.80 and had therefore good vision (for TV watching). Four males and one female had mild to serious red/green colour defects. One male had a blue/yellow colour defect.

3.2 Results stills
Overall picture “experience” stills:

The question whether Ambilight “adds“ something extra to the overall picture viewing experience clearly demonstrates that the “right” Ambilight setting can enhance the viewing experience for certain picture compositions (and vice versa !!!).

“Football” with Ambilight = relaxed enlarges / widens the picture for 57% of the participants.

“Red flower” with Ambilight = relaxed enlarges the picture for 21% of the participants, while 40% indicate other, positive experiences (more pleasant, more natural, more sunny etc.)

“Yellow flower” with Ambilight = relaxed is assessed positive by some 90% of the participants of which 66% favours the “enlargement” effect.

However:
“Yellow flower” with Ambilight = warm white shows no change with more than 40% of participants and 28% a negative change.

“Toyshop” with Ambilight = red is judged no-change or negative by more than 70% of participants, despite the fact that the picture contains considerable red.

“Football” with Ambilight = blue also scores more than 65% no-change or negative.

Colour matching and personal preference appear to be important factors for the appreciation of Ambilight. This explains why the active Ambilight -relaxed mode that adapts and matches the Ambilight “colour impression” and intensity to the picture on the screen is highly appreciated.

TV-picture brightness stills:
The brightness ratio between TV and its surroundings is assessed as clearly improved. For the Ambilight - relaxed setting 78% sees slightly to strong improvement, 8% no improvement and 14% is slightly negative. The Ambilight – warm white setting shows a somewhat less strong improvement (60% improvement, 9% no change, and 31% negative).

3.3 Results film scenes
Ambilight background lighting
Two Ambilight settings were used; the active relaxed mode and the passive warm white mode. Each was compared with a situation with no Ambilight.

The results show that overall Ambilight is judged as more pleasant by 76%, with 6% indifferent and 18% less pleasant for the active – relaxed mode. Slightly less favourable (68%) is the passive warm white mode. There is however a significant difference between the nature and action film scene for the relaxed mode with nature scoring > 90% more favourable (with almost 70% of participants scoring the maximum positive scale = a lot more pleasant), but the action film scoring roughly 60% more favourable (with 40% of participants scoring somewhat more pleasant, 20% much more pleasant, and more than 30% less pleasant).

Brightness ratio TV picture – surroundings
The assessment of the effect of Ambilight on the brightness ratio between the TV picture and TV surrounding background is comparable to the above appreciation of the Ambilight background results.

Psycho-fysiological effects
The Activation- Deactivation Adjective Checklist was used to compare a situation with no- Ambilight with Ambilight – warm white or Ambilight- relaxed. There is a significant difference in the effect of Ambilight for the three different types of video films (fig.2).

Figure 2, Psycho–fysiological scoring results for Ambilight relaxed mode illustrating differences between the viewing of the sports and nature film. For the nature film Ambilight does invoke feelings of overall relaxation, feeling at ease, calmness. The effect is the strongest with the Ambilight – relaxed setting. For the soccer film a similar effect is found but somewhat less pronounced. However, people do feel more lively and active especially with the Ambilight – relaxed setting. For the action film effects are minimal and mixed.

Influence of Ambilight on viewing experience: Apart from psycho-fysiological effects, Ambilight does have (visual) effects on the viewing experience. It appears that there are differences between the experience of a certain Ambilight setting and the nature of the film. With passive Ambilight- warm white some 20% experience no change, 30% consider the viewing experience for sport and nature as negative and the action film scores worse (40%). A variety of positive experiences is mentioned by the remaining 50- 40% (more intense, more movie theatre experience, more “connected,” enlarging effect etc.).

Figure 3: Example of viewing experience results for the active Ambilight – relaxed mode The active Ambilight setting-relaxed scores better (see fig. 3) especially with the nature and soccer film. Remarkable is the very positive experience for the nature film (15% see no or negative change but 85% have positive viewing experiences). Sports ranks second with 35% no or negative change and 65% with a positive experience. The action film scores mixed: 50% no or negative change and the remaining positive.

Influence of Ambilight on eye strain:

Figure 4 Influence of passive Ambilight (warm white) on eye strain

For all three films, passive Ambilight – warm white is experienced as relaxing for the eyes by 72% of the participants (fig.4). The active Ambilight – relaxed shows a lower percentage (59% experience relaxation) for the thriller film, while the nature film scores very high ( 83% ) with the soccer match as a good second (78%).

Preference for active versus passive versus no- Ambilight:
There are significant differences in the preference for the different kind of moving video scenes.

For the nature film 79% prefers the active – relaxed setting while only 8% prefers no Ambilight at all. For the thriller film opinions vary and 27% prefers no Ambilight at all, while the preference for active - relaxed versus passive – warm white is roughly the same (38% versus 35%).

For the sports film a small majority (52%) prefers the active – relaxed setting, 34% prefers the passive warm white setting. 14% prefers no Ambilight at all.

4. Discussion and conclusions
Under “home cinema” room lighting level (7 lux) by which the experiments were conducted Ambilight does improve the brightness ratio between the TV picture and the background surroundings significantly. Dependent on the Ambilight setting and the nature of the film 60 – 90% does rate the Ambilight favourable for reduced eye – strain. The Ambilight – relaxed setting is a clear winner. The explanation is simple: without Ambilight the ratio between picture -, immediate surrounding (side)- and overall wall luminance is e.g. for the soccer still 10: 0.4: 0.4. With Ambilight on (warm white setting) it becomes 10: 3: 0.7 which is very close to the ideal ratio of 10: 3: 1

The claim that Ambilight reduces eye – strain at home cinema – lighting conditions (7 lux) is generally correct in that 60- 90% of the people experience less strain dependent on the combination of Ambilight setting and the nature of the film/scene.

Ambilight can add a positive dimension to the viewing experience dependent on the nature of the film and the Ambilight setting. The active Ambilight –relaxed setting scores very positive with a nature film (85% of the people indicate a positive experience), positive with a soccer film (65%) and mixed (50%) with the action film. Most likely explanation for the low score for the action film is the “visual –desynchronization” between the Ambilight -changes and the brightness -changes and- distribution on the TV screen. Sometimes the edges of the screen are bright with Ambilight low and vice versa causing “unrest” and “visual confusion.”

For certain films/programmes that can be characterized by relatively “slow” changing backgrounds and overall picture brightness and brightness distributions within the picture the active Ambilight – relaxed setting is experienced as adding a very positive viewing experience.

In addition to the (visual) viewing experience the active Ambilight - relaxed setting does appear to have a positive effect on psycho-fysiological parameters that show a similar pattern as above mentioned viewing experience. With this setting the nature film induces a high degree of different kinds of “relaxing“ feelings compared to the other films, while sports shows higher scores for “active“ and “lively“ aspects. While overall the action film scores mixed for viewing experience it does show an increase for the parameters “active“ and “lively“ for the active Ambilight – relaxed setting, something that would be in line with the effects of an action film.

The active Ambilight – relaxed setting gives the possibility to add a new overall positive experience dimension to certain types of film/ programmes.

About the author
Dr. Ir. S.H.A. Begemann is a Philips professor at the Technische Universiteit Eindhoven ( Tue). He is based in the Netherlands at Ir. A.C. Westerlaken , Technische Universiteit Eindhoven ( Tue). He can be reached at ir.sha.begemann@philips.com.

5. Literature
1988, Tayer R. E., Takahashi, P.J. Pauli, J.A., Multidimensional arousal states, diurnal rhythms, cognitive and social processes, and extraversion, Personality and individual Differences, vol 9: 15 – 24 1988, Kerkhof G.A., Kerkhof, De Nederlandse versie van de Activation - Deactivation Adjective Checklist, Nederlands tijdschrift vd Psychologie, vol 53: 153 - 157

6. Translation table & figures

Table 1: Beoordeling helderheidverhoudingen tussen tv-beeld en omgeving = Judgment brightness ratioTV picture and surroundings Sterk verbeterd = strongly improved Iets verbeterd = somewhat improved Moeilijk te zeggen / geen verandering = difficult to say / no change Iets verslechterd = slightly deteriorated Sterk verslechterd = strongly deteriorated

Figure 2: Gevoelsaspecten = feelings/ sensations Meer = more Minder = less Geen verschil = no difference Ontspannen = relaxed Rustig = quiet/restful Op gemak = at ease Kalm = calm Vredig = peaceful Levendig = lively Vitaa l= vital Pittig = crisp/spirited Actief = active Krachtig = strong/robust Ingespannen = strenuous

Figure 3: Ja slechter = yes worse Nee = no Ja meer intens = yes more intense Ja ga er meer in op = yes become more involved/part of it Ja meer biooscoopervaring = yes more movie theatre experience Ja anders = yes different

Figure 4: Ja = yes Nee = no Kan niet zeggen = can not say Ontspannend voor ogen = relaxing for the eyes