1 Brightness Contrast and Visual Acuity in Daytime Museum Lighting Dewi Anisa Auriani Pribadi, Joice Sandrasari Architecture Department, Faculty of Engineering, University of Indonesia, Depok, 16424, Indonesia E-mail: [email protected]Abstract This research is based on a pursuit of theoretical explanation regarding inappropriate lighting condition in daytime museums located in Jakarta. The thesis focuses on brightness contrast between task and ambient lighting systems as the issue that has lessened the quality of vision inside such museums. The issue is further discussed by considering conservation guidelines, general perceived brightness, illuminance ratio, adaptation and glare. A relationship to visual acuity is also included to understand the contribution of brightness contrast in creating a relevant luminous museum environment. Analysis is based on comparison between museum lighting principles and data collected through observation and interviews in three case study museums, and visitor data collected through online questionnaire. The research shows that high task/ambient brightness contrast results in less visual comfort and less visual acuity. Adaptation and glare also contribute in determining visual acuity. The research also shows that none of all case study museums have successfully achieved relevant luminous museum environment. Keywords: museum lighting, brightness contrast, visual acuity, adaptation, glare Kontras Tingkat Terang dan Ketajaman Visual pada Pencahayaan Museum Abstrak Skripsi ini bertujuan untuk mencari penjelasan teoretis dari keadaan pencahayaan pada museum di Jakarta yang beroperasi pada siang hari. Penelitian ini berpusat pada kontras tingkat terang antara system pencahayaan Task dan Ambient yang mengurangi kualitas penglihatan di dalam museum tersebut. Pembahasan isu skripsi ini juga didukung dengan pedoman konservasi, tingkat terang umum, rasio illuminance, adaptasi, dan silau. Hubungannya dengan ketajaman visual juga dipertimbangkan untuk memahami kontribusi kontras tingkat terang dalam menciptakan lingkungan museum bercahaya yang relevan. Analisis didasarkan pada perbandingan antara prinsip pencahayaan museum, data observasi dan wawancara di tiga museum studi kasus, dan data pengunjung yang diperoleh melalui kuesioner online. Penelitian ini menunjukkan bahwa kontras tingkat terang yang tinggi pada sistem pencahayaan task/ambient mengurangi kenyamanan dan ketajaman visual. Adaptasi dan silau juga mempengaruhi ketajaman visual. Penelitian ini juga menunjukkan bahwa semua museum studi kasus belum berhasil menciptakan lingkungan museum bercahaya yang relevan. Introduction Conveying visual information regarding the exhibits is the main objective of a museum. Comfortable visual experience is a priority in creating an enjoyable journey inside the exhibition space. Therefore, it is important to provide appropriate lighting for the visitors. Appropriate lighting means creating a relevant luminous environment in which a visitor’s Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
15
Embed
Brightness Contrast and Visual Acuity in Daytime Museum ...
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Brightness Contrast and Visual Acuity in Daytime Museum Lighting
Dewi Anisa Auriani Pribadi, Joice Sandrasari
Architecture Department, Faculty of Engineering, University of Indonesia, Depok, 16424, Indonesia
This research is based on a pursuit of theoretical explanation regarding inappropriate lighting condition in daytime museums located in Jakarta. The thesis focuses on brightness contrast between task and ambient lighting systems as the issue that has lessened the quality of vision inside such museums. The issue is further discussed by considering conservation guidelines, general perceived brightness, illuminance ratio, adaptation and glare. A relationship to visual acuity is also included to understand the contribution of brightness contrast in creating a relevant luminous museum environment. Analysis is based on comparison between museum lighting principles and data collected through observation and interviews in three case study museums, and visitor data collected through online questionnaire. The research shows that high task/ambient brightness contrast results in less visual comfort and less visual acuity. Adaptation and glare also contribute in determining visual acuity. The research also shows that none of all case study museums have successfully achieved relevant luminous museum environment. Keywords: museum lighting, brightness contrast, visual acuity, adaptation, glare
Kontras Tingkat Terang dan Ketajaman Visual pada Pencahayaan Museum
Abstrak Skripsi ini bertujuan untuk mencari penjelasan teoretis dari keadaan pencahayaan pada museum di Jakarta yang beroperasi pada siang hari. Penelitian ini berpusat pada kontras tingkat terang antara system pencahayaan Task dan Ambient yang mengurangi kualitas penglihatan di dalam museum tersebut. Pembahasan isu skripsi ini juga didukung dengan pedoman konservasi, tingkat terang umum, rasio illuminance, adaptasi, dan silau. Hubungannya dengan ketajaman visual juga dipertimbangkan untuk memahami kontribusi kontras tingkat terang dalam menciptakan lingkungan museum bercahaya yang relevan. Analisis didasarkan pada perbandingan antara prinsip pencahayaan museum, data observasi dan wawancara di tiga museum studi kasus, dan data pengunjung yang diperoleh melalui kuesioner online. Penelitian ini menunjukkan bahwa kontras tingkat terang yang tinggi pada sistem pencahayaan task/ambient mengurangi kenyamanan dan ketajaman visual. Adaptasi dan silau juga mempengaruhi ketajaman visual. Penelitian ini juga menunjukkan bahwa semua museum studi kasus belum berhasil menciptakan lingkungan museum bercahaya yang relevan. Introduction Conveying visual information regarding the exhibits is the main objective of a museum.
Comfortable visual experience is a priority in creating an enjoyable journey inside the
exhibition space. Therefore, it is important to provide appropriate lighting for the visitors.
Appropriate lighting means creating a relevant luminous environment in which a visitor’s
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
2
need of activity and biological visual information needs are being fulfilled. This requires
considerations not only for visual acuity in observing the exhibits and reading written
explanations. Lighting design for museum environment also requires considerations of
illuminants for the surrounding in order to create an overall comfortable environment.
However, the needs for lighting in a museum must be kept in balance with the requirements
of conservation. This calls for attention to deterioration caused by UV radiation and visible
light spectrum. Therefore, both relevant lighting design and protection for conservation need
to be considered in the discussion of museum lighting design.
Unfortunately, the benefits of lighting design are yet to be fully experienced in museums
located in Jakarta. According to personal observation made during previous visits to these
museums, the interior spaces are rarely accommodated with appropriate lighting. Most of
these museums operate during work hours (between 8.00 a.m. to 5.00 p.m.). However, natural
light is hardly used appropriately as a light source. On the other side, artificial light installed
can hardly provide adequate lighting inside the museums. Dark spaces are commonly found
inside the exhibition space. Observing the exhibits and reading written explanations become a
struggle most of the time. Glare is also commonly found on the surface of glass on the
showcase.
The research objective is to find theoretical explanation of inappropriate lighting condition in
daytime museums found in Jakarta. Relationship between quantitative value of illuminance
ratio and qualitative value of brightness contrast is to be clarified in this research.
Relationship between brightness ratio, adaptation, glare, visual comfort and visual acuity is
expected to be understood by the end of this research.
The extent of this research includes basic understanding of lighting design, museum lighting
design principles and the perception of brightness contrast. Topics regarding human eye
adaptation, glare as distraction, as well as visual acuity are also considered. Visual acuity is
discussed in relation to the comfort level in observing exhibits and in reading written
explanations related to the display.
The case study includes three different museums located in Jakarta. The museums are
Museum Nasional Building A, Museum Nasional Building B and Museum Asmat Taman
Mini Indonesia Indah. The case study museums are chosen due to their similarities of daytime
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
3
operation hours and natural history exhibits. However, the three museums have
distinguishable lighting design character, which makes an interesting discussion. Data
collection of the museums includes current lighting condition, interviews and visitor past
experience inside the museums.
Literature Review Lighting design involves a series of distribution and manipulation of light sources to enhance
intended activity inside a space. However, museum lighting design must equally consider the
need of conservation to ensure safety of exhibits. On the other hand, visual comfort and visual
acuity of visitors must be maintained at all time. Therefore, understanding museum lighting
design must include a study of lighting design in general, museum conservation lighting
principles and basic understanding of visual perception. Specific to this research,
understanding of visual perception will be focusing on the perception of brightness.
Lighting determines how a space is perceived by the human eye. This perception can be
formed by receiving visual signals from both natural and artificial light sources. Natural light
source includes daylight from the sun and the sky. Artificial light source includes adjustable
sets of lamps, luminaires and mounting strategies which can be used to create different
lighting systems (Lechner, 2001).
Both natural and artificial lighting are available for use inside daytime museums. However,
specific to museum environment, visual needs for lighting must be balanced with protection
from deterioration for the exhibits. This applies strongly for fugitive materials which include
organic materials originating from living organisms. Protection from ultraviolet and visible
light must be appropriately assigned to exhibition space. Lessening exposure by reducing
illuminance and/or period of contact with visible light is preferable. Thomson (1978)
described that the standard maximum illuminance level for fugitive materials is 50 lux and the
standard maximum illuminance level for stronger materials is 150 lux. Artificial light is more
preferable in both cases since strong daylight is more dangerous yet less manageable.
Adaptation schemes must also be provided accordingly. The human eye must be given at least
a minute or so to adjust to new brightness level (Thomson, 1978), and complete adaptation
takes about an hour (Lechner, 2001).
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
4
These requirements should also be equipped with lighting quality that can create a relevant
luminous environment. Lam (1977) explained that a relevant luminous environment provides
sufficient lighting for the main activity. The main activity of observing exhibits in museums is
best accommodated with Task Lighting System. However, fulfilling biological information
needs in the background is also as important to achieve relevant luminous museum
environment. Therefore, Task Lighting System is usually equipped with Ambient Lighting
System for the surroundings. This creates a foreground-background lighting systems
relationship known as Task/Ambient Lighting System. Emphasis on exhibits by task lighting
system on the foreground ensures that the eye can freely see what it needs to see without any
distraction.
Distraction can be in a form of uncomfortable darkness or brightness level created by
inappropriate brightness contrast between task and ambient lighting systems. Theoretically,
the perceived level of brightness does not have any linear relationship with the measured
value of illuminance. Brightness is a relative value, meaning that it is perceived based on the
comparison with other visible brightness level. Hence, brightness can be observed in terms of
brightness contrast. Two different brightness contrasts create simultaneous contrast, which
can also affect how brightness in general is perceived. High brightness contrast can result in
distracting glare. Glare in itself can also be an additional distraction due to very high level of
illuminance. The absence of these distractions can greatly enhance visual acuity. Visual acuity
is the sharpness of vision. Visual acuity is very important for the main activity in museums
which includes the ability to see details of exhibits and to clearly read their explanation cards.
Research Method Theory literatures are collected from various sources prior to case study observation. Theory
researched includes basic understanding of lighting design, museum lighting design principles
and the perception of brightness contrast. Topics regarding human eye adaptation, glare as
distraction, as well as visual acuity are also considered. Visual acuity is discussed in relation
to the comfort level in observing exhibits and in reading written explanations related to the
display.
Case study museums located in Jakarta are researched through a series of observation,
documentation and interviews. The case study includes three different museums located in
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
5
Jakarta. The museums are Museum Nasional Building A, Museum Nasional Building B and
Museum Asmat Taman Mini Indonesia Indah. The case study museums are chosen due to
their similarities of daytime operation hours and natural history exhibits. However, the three
museums have distinguishable lighting design character, which makes an interesting
discussion.
Quantitative data related to existing lighting condition of the museums are collected during
survey visits to the museums. Supporting qualitative data is also collected during these visits
from personal observation and experience as well as interviews with museum staffs.
Quantitative data regarding visitor visual experience in the museums is collected through
online questionnaire forms. The summary of questionnaire data used is based on the answers
of 20 respondents per case study museum.
The overall theory gathered is used as basic principles in analysing the case study museums.
The data collected during survey visits to case study museums will be compared to respective
questionnaire results. The analysis on the three museums results in the explanation of current
lighting conditions in daytime museums located in Jakarta.
Results and Discussion The case study museums are chosen based on three characteristics: (1) located in Jakarta, (2)
operates during daytime, and (3) displays natural history exhibits. Similarity in location
makes a more relevant sunlight distribution comparison. Daytime operation time makes sure
that both natural and artificial light sources are taken into account. Natural history exhibits is
chosen for the similarity of material strength, which determines 50/150 maximum illuminance
guideline to use.
The three chosen case study museums are Building A and Building B of Museum Nasional in
Central Jakarta, and Museum Asmat of Taman Mini Indonesia Indah in East Jakarta. The
explanation of each museum will include short history and background and current lighting
condition. Proportion of light sources, adaptation schemes and glare will be included.
The analysis will be focusing on brightness contrast between task lighting as foreground
lighting system and ambient lighting as background lighting system. General perception of
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
6
brightness inside the space will also be considered as qualitative measure. Task/Ambient
illuminance ratio will also be included as a comparison.
Table 1: Summary of Case Study Observation
Values
Case Study 1 Case Study 2 Case Study 3
Indonesian Ethnography
Exhibition of Museum Nasional, Jakarta
Humanity and Science and
Technology and Economy
Exhibition of Museum Nasional,
Jakarta
Museum Asmat Taman Mini
Indonesia Indah, Jakarta
Adaptation before entering Sufficient in time span but not in standard illuminance* *scheme 2
Sufficient in time span and standard illuminance
Insufficient both in time span and standard illuminance
The visitor eye is not ready
The visitor eye is ready
The visitor eye is not ready
General Proportion of Light Sources Daylight is dominant Artificial Light is dominant
Daylight is dominant
Sumatera-Java Annex Java Bali-Papua
Section1,2 Section 3 Section 4a,4b
Section 1,2,3 Corridor A,B
General Proportion of Task/Ambient Brightness
Ambient is dominant Task is dominant Ambient is dominant
Sumatera-Java Annex Java Bali-Papua
Section 1 Section 2,3 Section 4a,4b
Section 1,2,3 Corridor A,B
General Brightness
Spread Mostly Darker and Standard
Mostly Darker and Standard
Mostly Darker and Standard
General Brightness in relation to Task/Ambient Brightness contrast
There is a linear relationship (The higher brightness contrast, the darker)
There is a linear relationship (The higher brightness contrast, the darker)
There is a linear relationship (The higher brightness contrast, the darker)
General Brightness in relation to Illuminance Ratio
No linear relationship
No linear relationship
No linear relationship
Illuminance Ratio
Spread Mostly too low or too high
Mostly standard and too low
Mostly too low
Illuminance ratio in relation to Task/Ambient Brightness Contrast
No linear relationship No linear relationship
No linear relationship
Illuminance Ratio in relation to General Brightness
No linear relationship
No linear relationship
No linear relationship
Breach of 50 lux Yes, in 3/5 Sections Yes, in 1/5 Sections
Yes, in 2/5 Sections
Glare Direct glare Discomfort Discomfort Discomfort
Indirect Glare on Showcase
Disability and Discomfort
Discomfort Discomfort
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
7
The comparison of the three case study museums is shown in Table 1. The lighting quality of
each museum seems to vary. Case Study 2 can be said to be the best of the three, since it has
the least breach of 50 lux maximum illuminance, preserves the dominance of task lighting and
artificial light source use, provides sufficient adaptation scheme, and manages to avoid
disability glare at the same time. Case Study 3 comes second since breach of 50 lux maximum
illuminance and disability glare is still avoided despite other lighting qualities similar to Case
Study 1.
The data collection has also answered some of the questions of the research. Firstly,
task/ambient illuminance ratio does not directly determine or have any linear relationship with
task/ambient brightness contrast. Hence, there must be other factors that help determine the
perception of brightness inside a space.
The pattern in each case study museum shows that where daylight is dominant, ambient light
appears much brighter to the observer. This is most likely because artificial light in most of all
three museums are specifically located to highlight the exhibits. Therefore, the observer’s
brain automatically categorizes daylight as ambient light. This assumption applies even more
in Case Study 1 and Case Study 3, since Case Study 2 does not readily have a large number of
windows compared to the other two. The strong ambient light hence makes the task artificial
light appears much darker.
This shows that brightness is indeed first and foremost a relative value. The perception of
brightness is largely determined by comparison of coexisting brightness levels inside the
space. The explanation also shows that strong daylight upsets the intended lighting system
priority. Visitors must be able to freely see the exhibits they need and want to see. However,
the strong daylight and therefore the strong ambient lighting it creates overpowered the more
relevant signal of task lighting. In other words, the background becomes a distraction for the
foreground. Case Study 2 shows that artificial light can still provide good quality of ambient
light as substitute for the less controllable daylight.
This is an important issue, since the focus selector is automatically attracted to unusual
qualities, in this case the brighter signal. This means that if the visitors would like to
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
8
consciously see the exhibits in Case Study 1 and Case Study 2, they have to concentrate
harder to ignore the bright ambient background. This is even harder to be done since there is
still adaptation and glare issues that the visitors have to deal with at the same time.
Therefore, in order to provide relevant luminous environment, light sources emitting extreme
brightness anywhere inside the space should be avoided. We must at least make sure that
brightness contrast is preserved constantly throughout the space to eliminate distracting
brightness contrast.
Secondly, the comparison also shows that the higher the brightness contrast between task and
ambient lighting, the darker the museum space is perceived. This is true despite of any
measured illuminance ratio, light source proportion, adaptation scheme and glare level. The
perception of general brightness has also shown the importance of simultaneous contrast.
Adjacent spaces with the same task/ambient brightness ratio is perceived similarly in terms of
general brightness. On the other hand, adjacent spaces with different brightness ratio will
have different general perceived brightness. This shows that visible brightness contrast from
adjacent spaces is added into the comparison in determining general brightness of the space
we inhabit.
Hence, it is important to understand that preservation of brightness contrast throughout the
exhibition space as a whole is very important. Preserved brightness contrast inside one
exhibition section can be upset by another section with different brightness contrast. This will
make the space appear darker or brighter than intended. When the space appears darker as a
result, biological comfort of visitors may be affected negatively. This will reduce the
relevance of the luminous environment.
In order to understand further about the effect of brightness contrast to visual experience of
visitors, a study of visual comfort and visual acuity will be discussed in the next chapter. The
relationship between brightness contrast, adaptation and glare will also be discussed further in
the next chapter.
Online questionnaire response from selected 20 respondents for each museum is used to
collect visitor data to support the analysis. The data will also be used to reassess data gathered
in the previous chapter. Questions regarding proportion of light sources proportion, adaptation
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
9
inside exhibition space, general perception of bright and dark areas, indirect glare on
showcase glass surface and inclination to revisit are also included as supporting data.
Table 2 shows that in general, artificial light gains more favour from the respondents. This
shows that daylight is indeed perceived as distraction due to its strong intensity. It seems that
respondents also associates daylight as ambient light, and therefore bothered when it takes
over the intensity of artificial light. It seems that the strong daylight in Case Study 1 makes
the artificial light appear less helpful, evident from the general perception of light sources
being distractive.
Table 2: Summary of Comparison between Case Study Observation and Questionnaire Respondent Answers
Values
Case Study 1 Case Study 2 Case Study 3
Indonesian Ethnography Exhibition of
Museum Nasional, Jakarta
Humanity and Science and
Technology and Economy Exhibition of Museum Nasional,
Jakarta
Museum Asmat Taman Mini
Indonesia Indah, Jakarta
Adaptation Prior to entrance to exhibition space
Sufficient in time span but not in standard illuminance* *scheme 2
Sufficient in time span and standard illuminance
Insufficient both in time span and standard illuminance
The visitor eye is not ready
The visitor eye is ready
The visitor eye is not ready
First Impression Dark Bright Bright**
Overall Impression
Dark* *one respondent changed to bright after visiting for more than an hour
Bright Bright** **two respondents mentioned dark upon entering and leaving, after visiting for less than 30 minutes
Light Sources General Proportion of Light Sources
Daylight is dominant Artificial Light is dominant
Daylight is dominant
Influence of light sources in General
Distracting Helpful Helpful
Artificial Light is more favoured
Artificial Light is more favoured
Artificial Light is more favoured
Task/Ambient brightness
General Proportion of Task/Ambient Brightness
Ambient is dominant Task is dominant Ambient is dominant
General perceived brightness
Spread Mostly Darker and Standard
Mostly Darker and Standard
Mostly Darker and Standard
General perceived brightness as mentioned by
More dark than bright areas
More dark areas than bright areas
More bright areas than dark
Kontras Tingkat..., Dewi Anisa Auriani Pribadi, FT UI, 2014
10
Case Study 1 and Case Study 2 shows that the better the adaptation scheme, the brighter the
space is perceived despite of the low illuminance level. However, Case Study 2 shows that
despite lack of adaptation, the space can still be perceived as bright. This is probably due to
the strong daylight distributed to the interior from open double-doors. Respondents have also
maintained their first impression of brightness until the end of their visit. However, one
respondent spending more than an hour inside Case Study 1 changed their impression to
bright. This shows that after the eye is given enough time to adjust inside exhibition space, the
perception of general brightness can still be altered.
The general brightness inside the space is perceived differently in each case study.
Respondents see more dark areas than bright areas in Case Study 2. One might argue that it is
due to the absence of extreme daylight distribution. However, respondents see more bright
areas than dark areas only in Case Study 3, although Case Study 1 also has strong daylight
distribution. Therefore, strong daylight might not be the only determinant. Most likely, the
other factor is the distributional pattern of daylight itself. Even though daylight is not
distributed evenly inside each section in Case Study 3, it is distributed in a consisted pattern
throughout the whole museum. Therefore, the consistent pattern set the general brightness
inside the museum by maintaining the same simultaneous contrast combination.
Case Study 1 suffers from the danger of disability glare on showcase glass covers. This is a
great concern, since disability glare means that visitors are unable to receive important visual
signal from the exhibits, let alone to observe detail and properly read explanation texts. Most
respondents Glare Direct glare Discomfort Discomfort Discomfort