CEN/TS 16163:2014

SLOVENSKI STANDARD
01-julij-2014
2KUDQMDQMHNXOWXUQHGHGLãþLQH6PHUQLFHLQSRVWRSNL]DL]ELURXVWUH]QH
UD]VYHWOMDYH]DUD]VWDYHY]DSUWLKSURVWRULK
Conservation of Cultural Heritage - Guidelines and procedures for choosing appropriate
lighting for indoor exhibitions
Erhaltung des kulturellen Erbes - Leitlinien und Verfahren für die Auswahl geeigneter
Beleuchtung für Innenausstellungen
Conservation du patrimoine culturel - Lignes directrices et procédures concernant le
choix d'un éclairage adapté pour les expositions en intérieur
Ta slovenski standard je istoveten z: CEN/TS 16163:2014
ICS:
91.160.10 Notranja razsvetljava Interior lighting
97.195 Umetniški in obrtniški izdelki Items of art and handicrafts
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CEN/TS 16163
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
April 2014
ICS 97.195
English Version
Conservation of Cultural Heritage - Guidelines and procedures
for choosing appropriate lighting for indoor exhibitions
Conservation du patrimoine culturel - Lignes directrices et Erhaltung des kulturellen Erbes - Leitlinien und Verfahren
procédures concernant le choix d'un éclairage adapté pour für die Auswahl geeigneter Beleuchtung für
les expositions en intérieur Innenausstellungen
This Technical Specification (CEN/TS) was approved by CEN on 14 October 2013 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 16163:2014 E
worldwide for CEN national Members.

Contents Page
Foreword .4
Introduction .5
1 Scope .6
2 Normative references .6
3 Terms and definitions .6
4 Symbols . 11
5 Sensitivity of cultural property to light . 12
5.1 General . 12
5.2 Mechanisms of damage . 12
5.2.1 General . 12
5.2.2 Photochemical . 12
5.2.3 Radiant heating . 13
5.2.4 Biological effects . 13
5.3 Sensitivity and classification for cultural property . 14
5.4 Limitations for total luminous exposure . 14
6 Light measurement . 15
6.1 Measurement of illuminance . 15
6.2 Measurement of UV radiation . 16
7 Exhibition lighting. 16
7.1 General . 16
7.2 Viewing conditions . 16
7.3 Visual adaptation . 16
7.4 Contrast ratios . 17
7.5 Colour appearance . 17
7.6 Colour rendering . 17
7.7 Backgrounds to exhibits . 18
7.7.1 General . 18
7.7.2 Luminance of backgrounds . 18
7.7.3 Colour of backgrounds . 18
7.8 Glare . 19
7.9 Modelling . 20
7.10 Historic furnishings & interiors . 21
7.11 Simulation and mock-ups . 21
Annex A (informative) Characteristics of light sources . 22
A.1 Daylight . 22
A.2 Electric sources . 22
A.2.1 General . 22
A.2.2 Incandescent lamps . 23
A.2.3 Fluorescent lamps . 24
A.2.4 Solid State Lighting . 24
A.2.5 Metal Halide lamps. 26
Annex B (informative) Glasses and films characteristics . 27
B.1 Glasses . 27
B.2 Window films . 27
B.3 Other protection . 27
Annex C (informative) Filters . 28
Annex D (informative) Relative damage . 29
Annex E (informative) Lamps and lighting attachments . 30
Bibliography . 31

Foreword
This document (CEN/TS 16163:2014) has been prepared by Technical Committee CEN/TC 346
“Conservation of Cultural Heritage”, the secretariat of which is held by UNI.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria, Croatia, Cyprus,
Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,
Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Introduction
Lighting is needed for many specific functions in museums and other cultural heritage buildings, for example,
for research, conservation and permanent or temporary exhibitions. Lighting is one of the most important
factors enabling visitors to fully enjoy works of art and other cultural property. In fact, lighting is a key medium
in which visitors interpret and appreciate cultural heritage. Enough light is needed to see well but this may
present a challenge when what is being viewed will deteriorate in the presence of light. Where cultural
heritage is judged to be worth preserving for future generations it is essential to consider the controlled use of
light. Indeed, light is an environmental factor, which is a threat to many objects. Alone or in combination with
other environmental factors (temperature, humidity, pollution, etc.) light causes fading, discoloration and
embrittlement of a wide range of materials. This damage is cumulative and irreversible: no conservation
treatment can restore change of colour or loss in strength of materials damaged by light. Therefore, the
challenge of museum exhibition lighting is to find an appropriate compromise between the long term
preservation of the exhibit and the needs of visitors to view them within a suitable exhibition design. As an
integral part of exhibition lighting, the following aspects should be considered:
— the conservation aspect, related to the sensitivity of the exhibit at different wavelengths of the incident
radiant energy, the spectral composition of the light source and the total luminous exposure,
— the visual aspect, related to the impact of lighting on the visitor experience: lighting has to allow visitors to
see exhibits on display, with the correct colour perceptions without glare, reflections or insufficient
illumination,
— the design aspect related to the concept and position of the exhibition architecture, the point of view of
the curator and all others involved in the scenographic and/or didactic objectives of the exhibition.
Due to its non-technical nature the last mentioned aspect cannot be dealt with in this Technical Specification.
This Technical Specification uses terms defined in European (EN 12665 and EN 15898) and International
(CIE International lighting vocabulary) terminology standards, but their definitions have been adapted to the
intended users of this specification.
1 Scope
This Technical Specification defines the procedures as well as the means to implement adequate lighting, with
regard to the conservation policy. It takes visual, exhibition and conservation aspects into account and it also
discusses the implications of the lighting design on the safeguarding of cultural property. This Technical
Specification gives recommendations on values of minimum and maximum illumination levels. It aims to
provide a tool for setting up a common European policy and a guide to help curators, conservators and project
managers to assess the correct lighting that can assure the safeguarding of the exhibits. This Technical
Specification covers lighting for heritage objects on exhibition in both public and private sites and does not
consider lighting in other cultural heritage contexts such as open-air collections, etc.
2 Normative references
Not relevant.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
accent lighting
lighting focused on an exhibit or a group of exhibits to emphasize them
[SOURCE: CIE S 017/E:2011]
3.2
annual luminous exposure
H
m
total luminous exposure per year (unit: lux hours per years, lx h / a)
Note 1 to entry: One year of museum display is approximately 3 000 h. See also 3.35.
3.3
blue wool test: test for light fastness
certified set of eight pieces of wool each dyed with a different specific blue dye graded to fade after a set
exposure to light
[SOURCE: ISO 105-B08:1995]
Note 1 to entry: This system is usually referred as Blue Wool Standard (BWS) and it is used in museums to assess the
radiation exposure of materials. The eight wool pieces are numbered #1 to #8, each about 2 to 3 times as sensitive as the
next. High sensitivity is defined as materials rated #1, #2, or #3; medium as #4, #5, or #6; and low as #7, #8. A panel of
selected blue wool samples is left at the measurement point and after a period it can be seen which samples have faded
and the dose of light received determined.
3.4
colour rendering
effect of an illuminant on the colour appearance of exhibits by conscious or subconscious comparison with
their colour appearance under a reference illuminant
[SOURCE: CIE S 017/E:2011 or IEC-IEV:1987, 845-02-059]
3.5
colour rendering index
R
a
derived from the colour rendering indices for a specified set of 8 test colour samples
Note 1 to entry: Ra has a maximum of 100, which generally occurs when the spectral distributions of the light source
and the reference light source are substantially identical.
[SOURCE: CIE S 017/E:2011 or IEC-IEV:1987-845-02-61 and CIE 015:2004]
3.6
colour temperature
T
c
temperature of a Planckian radiator whose radiation has the same chromaticity as that of a given stimulus
(unit: kelvin, K)
[SOURCE: CIE S 017/E:2011 or IEC-IEV:1987, 845-03-049; see also CIE 015:2004]
3.7
cultural heritage
tangible and intangible entities of significance to present and future generations
Note 1 to entry: The term “exhibit” is used in this standard for cultural heritage. In specific professional contexts, other
terms are used: e.g. "artefact", “cultural property", “item”.
[SOURCE: EN 15898]
3.8
damage potential
Pdm
ratio of effective damaging irradiance and the illuminance at a point on the surface for a specific light source
(unit : W/lm)
3.9
daylight
visible part of global solar radiation
Note 1 to entry: When dealing with actinic effects of optical radiation, this term is commonly used for radiations
extending beyond the visible region of the spectrum.
[SOURCE: IEC-IEV:1987, 845-09-84]
3.10
daylighting
lighting for which daylight is the light source
[SOURCE: CIE S 017/E:2011]
3.11
daylight factor
D
ratio of the illuminance at a point on a given plane due to the light received directly or indirectly from a sky of
assumed or known luminance distribution, to the illuminance on a horizontal plane due to an unobstructed
hemisphere of this sky, excluding the contribution of direct sunlight to both illuminances
Note 1 to entry: Glazing, dirt effects, etc. are included.
Note 2 to entry: When evaluating the lighting of interiors, the contribution of direct sunlight needs to be considered
separately.
[SOURCE: CIE S 017/E:2011 and IEC-IEV, 1987, 845-09-087]
3.12
dosimeter
indicator measuring total irradiant exposure during a given time
Note 1 to entry: The above definition is valid in the context of the present Technical Specification and concerns with
the light measurement only.
3.13
effective damaging irradiance
E
dm
radiant flux per unit area at a point on the surface weighted by the relative damage action spectrum (unit: watt
-
per square metre, W m ²)
3.14
effective irradiance
E : E = ∫ Ε s(λ) dλ
eff eff e,λ
irradiance weighted on the spectral sensitivity of the materials constituting the exhibit
3.15
exhibit
object on display illuminated by natural and/or artificial light
3.16
filter
any device that modifies or reduces a portion of the electromagnetic spectrum
Note 1 to entry: Common filters are: coloured and neutral filters, conversion temperature blue (CTB) and conversion
temperature orange (CTO) filters, UV or IR absorbing filters. Neutral-density filters decrease the transmitted light by a
known amount without selecting any particular wavelength.
3.17
illuminance (at a point of a surface)
E
ratio of the luminous flux dΦ incident on an element of the surface containing the point, to the area dΑ of that
-2
element (unit: lux, lx = lm⋅m )
Note 1 to entry: It represents the quantity of light impinging on a surface.
[SOURCE: IEC-IEV, 1987, 845-01-038]
3.18
infrared radiation
IR
part of the electromagnetic spectrum with wavelength longer than those of the visible radiation, from about
780 nm to tens of micrometres
3.19
irradiance
E
e
-
radiometric quantity; the radiant flux per unit area at a point on the surface (unit: watt per square metre, W m ²)
3.20
lamp
source made in order to produce an optical radiation, usually visible
Note 1 to entry: This term is also sometimes used for certain types of luminaires (see below).
[SOURCE: CIE S 017/E:2011 and IEC-IEV, 1987, 845-07-003]
3.21
light
radiation that is considered from the point of view of its ability to excite the visual system
Note 1 to entry: It corresponds to the so-called visible radiation in the range between 380 nm and 780 nm.
Note 2 to entry: In the field of conservation, this term sometimes extends the range outside the visible portion,
including parts of the ultraviolet (UV) and near infrared (IR) regions.
[SOURCE: CIE S 017/E:2011]
3.22
luminaire
apparatus which distributes, filters or transforms the light transmitted from one or more lamps and which
includes, except the lamps themselves, all the parts necessary for fixing and protecting the lamps and, where
necessary, circuit auxiliaries together with the means for connecting them to the electric supply
[SOURCE: CIE S 017/E:2011 or IEC-IEV 1987-845-10-001]
3.23
luminance
L
quantity defined by the formula:
dΦ
L=
dAcosϑdΩ
where
is the luminance in a given direction or at a given point of a surface
L
is the luminous flux transmitted by an elementary beam passing through the given point and propagating in the
dΦ
solid angle dΩ containing the given direction
is the area of a section of that beam containing the given point
dA
is the solid angle
dΩ
is the angle between the normal to that section and the direction of the beam
ϑ
–2 –2 –1
(unit: cd·m = lm·m ·sr )
Note 1 to entry: It corresponds to the light coming from a surface.
[SOURCE: CIE S 017/E:2011 or IEC-IEV, 1987, 845-01-035]
3.24
luminous flux
Φ
photometric quantity derived from the radiometric quantity radiant flux (radiant power) by evaluating the
radiation according to the spectral sensitivity of the human eye (as defined by the CIE standard photometric
observer) (unit: lumen, lm)
Note 1 to entry: It is the luminous power emitted by a source or received by a surface.
Note 2 to entry: For the practical use of this document, in this definition, the values used for the spectral sensitivity of
the CIE standard photometric observer are those of the spectral luminous efficiency function V(λ) (photopic vision).
Note 3 to entry: See CIE S 017/E:2011 or IEC-IEV, 1987, 845-01-22 for the definition of spectral luminous efficiency,
845-01-23 for the definition of the CIE standard photometric observer and 845-01-56 for the definition of luminous efficacy
of radiation and ISO 23539:2005(E)/CIE S 010/E:2004.
3.25
luminous intensity
I
-1
luminous flux per unit solid angle in that direction (unit: candela, cd = lm sr ; sr = steradian)
Note 1 to entry: It is the luminous flux on a small surface, divided by the solid angle that the surface subtends at the
source (CIE S 017/E:2011 or IEC-IEV, 1987, 845-01-31).
Note 2 to entry: The candela is the base SI photometric unit. For its definition, see CIE S 17/E:2011 or IEC-IEV, 1987,
845-01-050 or the BIPM SI Brochure.
3.26
lux
symbol lx; SI unit of illuminance
Note 1 to entry: For more information see CIE S 17/E:2011 or IEC-IEV, 1987, 845-01-052 or the BIPM SI Brochure.
3.27
photometric quantities
quantities that are based on the perception of radiation by the human eye and are valid only for visible
radiation
3.28
radiant flux
Φ
e
radiometric quantity representing the radiant energy transported per unit time into a region of space by
electromagnetic waves (unit: watt, W)
3.29
reflectance
ρ
ratio of the reflected radiant or luminous flux to the incident flux in the given conditions
[SOURCE: IEC-IEV, 1987, 845-04-058]
3.30
relative damage potential
ratio of the damage potential of a specific light source and the damage potential of the CIE standard Illuminant
A (2 856 K) (equals to the incandescent lamp); it is dimensionless and assumes values between 0 and 1
3.31
relative damage action spectrum
s(λ)
dm,rel
describes the wavelength dependence of the photochemical damage properties, such as fading; it is
dimensionless and assumes values between 0 and 1
s(λ) =α(λ)⋅ ⋅ f(λ)
dm,rel
λ
where
is the spectral absorbance
α(λ)
is a function of wavelength determined by the receiving material
f(λ)
Note 1 to entry: It is normalised at 300 nm so that s(λ) = 1 for λ = 300 nm (see also Figure 1).
dm,rel
[SOURCE: CIE 157:2004]
3.32
sensitive exhibits
museum exhibits, which can be more or less affected by electromagnetic radiations and/or other
environmental factors
3.33
source
object that produces light or other radiant flux
[SOURCE: CIE S 17/E:2011]
3.34
spectral sensitivity
s(λ)
describes the wavelength dependence of the material properties, such as fading; it is dimensionless and
assumes values between 0 and 1
3.35
total luminous exposure
H
photometric quantity; it is the product of the illuminance by the time of the exhibit exposure; it is measured in
lux·hours [lx·h]
3.36
ultraviolet radiation
UV
part of the electromagnetic spectrum with wavelengths from 10 nm to 380 nm
Note 1 to entry: In the museum context UV is usually considered to include wavelengths up to 400 nm.
4 Symbols
The notations adopted in this TS are summarized below.
Table 1 — Symbols
a
Symbol Quantity
Unit
H lux-hours per year, lx⋅h per year Annual luminous exposure
m
R 1 Colour Rendering Index
a
T kelvin, K Colour temperature
c
P watt/lumen, W/lm Damage potential
dm
D 1 Daylight factor
-2
E watt per square metre, W⋅m Effective damaging irradiance
dm
-2
E watt per square metre, W⋅m Effective irradiance
eff
-2
E lux, lx=lm⋅m Illuminance
-2
E watt per square metre, W⋅m Irradiance
e
-2 -2 -1
L candela per square metre, cd⋅m =lm⋅m ⋅sr Luminance
Φ lumen, lm Luminous flux
-1
I Luminous intensity
candela, cd= lm⋅sr
Φ watt, W Radiant flux
e
ρ 1 Reflectance
s(λ) 1 Relative damage action spectrum
dm,rel
s(λ) 1 Spectral sensitivity
H lux⋅hours, lx⋅h Total luminous exposure
a
non dimensional units are indicated by 1
5 Sensitivity of cultural property to light
5.1 General
Light is one of several environmental factors to be considered in establishing a conservation policy.
A prerequisite for optimal lighting is good knowledge of present environmental conditions in the exhibition
area. This can be obtained by regularly monitoring lighting conditions by means of regular measurements to
account for daily and seasonal variations. Regular monitoring is recommended also after the first set up to
provide information on the environmental conditions, so that corrective actions can be taken if necessary.
5.2 Mechanisms of damage
5.2.1 General
Light may damage vulnerable exhibits by three mechanisms:
— Photochemical,
— Radiant heating effect,
— Growth of biological organisms.
The extent to which materials deteriorate under given lighting conditions depends on their chemical
composition, the characteristics of the light source, the illuminance levels and the length of exposure.
5.2.2 Photochemical
The absorption of light by a molecule or an ion can induce chemical changes, which result in changes of the
mechanical properties and the colour of the material, thus altering the exhibit in an irreversible way. For the
majority of light sensitive exhibits the damage is caused by the quantity of light (luminous exposure) and its
spectral distribution. The effectiveness of damage exponentially increases with the decreasing wavelength.
This means that usually the energy radiation of UV is much more damaging than blue light; blue light is more
damaging than green light, and so on (see Figure 1).
Accordingly, it is recommended to minimize the presence of UV in display lighting. The maximum acceptable
relative level of UV is 75μW/lm. This figure was originally chosen as it represented the amount of UV
produced by tungsten lamps which were at that time regarded as safe for lighting exhibits. Indeed, lower
relative levels of UV (such as 10μW/lm) can be attained either by using UV absorbers, on windows and
electric light sources, or by employing sources with minimal or zero UV output, such as most white LEDs.
However, the elimination of UV for sensitive exhibits is not sufficient to avoid damage if visible light is not
controlled and maintained below the values given in Table 3.
Key
X wavelength in nm
-0.012 (λ/[nm] -300)
Y s(λ) = e
dm,rel
Figure 1 — Relative damage Y to photochemically sensitive surfaces versus wavelength X of incoming
radiation
NOTE This graph is applicable for all Cat 2,3 and 4 exhibits (except newspapers), see also Table 2.
It has to be stressed that molecules, which make up the material, shall absorb radiation for a photochemical
process to occur. For example, with a blue exhibit the blue light is being reflected from it and all other
wavelengths absorbed by the material, so in this instance, green radiation will affect the exhibit more than blue
or violet radiation. Accordingly, the spectrum of the lighting source has to be considered in comparison with
the absorption spectrum of the more light sensitive molecules that occur in the material constituting the
artefact by evaluating the effective irradiance.
Photochemical action of light by itself is independent of the surrounding environment, but the subsequent
photochemical processes can be affected by other environmental factors such as temperature and relative
humidity, oxygen and atmospheric pollutants.
5.2.3 Radiant heating
The energy supplied by radiation raises the temperature of the surface on which radiation impinges,
depending on the amount of radiation that is absorbed, thermal conductivity within the exhibit, and convective
exchanges. This may lead to expansion and thermal stress on the artefact, and desiccation, which can be
caused by a decrease in local relative humidity due to the temperature rise. A higher temperature accelerates
chemical reactions and photochemical processes. Radiation just beyond the visible red is called infrared
radiation (IR) and is simply radiant heat. Thus, choosing light sources with little or no IR will reduce heat stress
on the material being lit. However, it needs to be stressed that intense light could also produce heating effects.
5.2.4 Biological effects
Some phototrophic micro-organisms may live under specific wavelengths, particularly when combined with
high relative humidity. Biological problems should be addressed by a team of specialists.
5.3 Sensitivity and classification for cultural property
Table 2 lists materials in four categories according to their sensitivity to light, but it does not consider possible
damage due to heating effects.
Table 2 — Light Sensitivity classification of cultural property from CIE 157:2004
Category Material description
1. No sensitivity The exhibit is entirely composed of materials that are insensitive to light. Examples;
most metals, stone, most glass, ceramic, enamel, most minerals.
2. Low sensitivity The exhibit includes durable materials that are slightly light sensitive. Examples; most
oil and tempera painting, fresco, un-dyed leather and wood, horn, bone, ivory, lacquer,
some plastics.
3. Medium sensitivity The exhibit includes fugitive materials that are moderately light sensitive. Examples;
most textiles, watercolours, pastels, prints and drawings, manuscripts, miniatures,
paintings in distemper media, wallpaper, and most natural history exhibits, including
botanical specimens, fur and feathers.
4. High sensitivity The exhibit includes highly light sensitive materials. Examples; silk, colorants known to
be highly fugitive, most graphic art and photographic documents.
5.4 Limitations for total luminous exposure
The photochemical effect is cumulative and it is closely related to the total radiation absorbed by the exhibit. In
the usual museum conditions the net photochemical effect on exhibits is the result of the total exposure. In
other words, it is the cumulative effect on the exhibit lifetime, which matters. To assess the overall impact of
light on an exhibit the annual luminous exposure is considered (expressed as lx•h per year).
Table 3 gives the recommended values of limiting illuminance and annual luminous exposure for the different
classes of light sensitive exhibits. When more than one class of material is present, the limit to be considered
corresponds to the most sensitive class.
Table 3 — Limiting illuminance and annual luminous exposure for different classes of light sensitive
exhibit interpreted from CIE 157:2004
Material classification ISO Blue Wool Upper limit annual Annual exposure time Illuminance
Standard luminous exposure
(BWS)
1. Insensitive
- no limit (for no limit (for no limit (for
conservation) conservation) conservation)
2. Low sensitivity 7 & 8 600 000 lx·h per year a 200 lx
3 000 h per year
3. Medium sensitivity
4, 5 & 6 150 000 lx·h per year a 50 lx
3 000 h per year
4. High sensitivity 1, 2 & 3 15 000 lx·h per year b 50 lx
300 h per year
a
Typical annual opening hours
b
Resulting annual hours using 50 lx
The recommended limiting illuminances are based on the recommendations of diverse international
authorities, such as AFE (Association Française de l’Eclairage), CIBSE (The Chartered Institution of Buildings
Services Engineers) and IESNA (Illuminating Enginering Society of North America). These figures are a
practical compromise between presentation and protection of exhibits in indoor exhibitions with lighting. If the
limiting illuminance is exceeded, the rate of fade and damage to materials will increase. On the contrary, it has
to be considered that lighting levels much below 50 lx, suggested for the Class 3 and 4, will result in poor
viewing conditions and loss of perception of colour and surface details.
It should be taken into account that other physical or chemical factors (relative humidity, temperature,
pollutants) can increase the adverse effects of light, so that in critical environmental conditions the above
reported limits are strictly recommended. It has to be noted that in case 4 of the Table 3 15 000 lx•h /a
corresponds to just 300 h exposure per year at a 50 lx illuminance (the minimum light level for discernment of
colour and detail on an exhibit). Therefore, exhibits of high sensitivity to light should be removed from display
into dark storage when their exposure limit is reached. Thus, a silk dress may be on permanent display at 50
lx, for eight hours per day, six days per week, for less than two months before reaching its annual exposure
limit and needing to be put into dark storage. If the same dress was in a display case at 10 lx , but boosted by
a proximity sensor to 50 lx when someone approaches, then the display period could be extended.
The actual damage potential of the spectrum of light from a particular light source on a particular material can
also be taken into account to allow some flexibility in the annual exposure limits given in the Table 3. Annex D
provides a summary of the relative damage potential for various combinations of light sources and filters.
6 Light measurement
6.1 Measurement of illuminance
Illuminance is measured with illuminance-meters, usually called lux-meters, using sensors that have a spectral
response that matches that of the human eye. Several types of devices are available to measure indoor light
levels, from simple hand-held meters to small units that transmit their readings back to a central data logger.
Many of the hand-held meters have the measuring sensor on a lead that allows it to be placed on the surface
being measured whilst the meter itself can be held close to the user so the readings can be easily seen.
Meters should have a ‘hold’ button that allows a reading at arm’s length to be held until the meter can be
brought close enough to be read. Measuring ranges for indoor illuminance-meters for conservation use should
be in the range 10 lx to 10 000 lx and comply with CIE 69-1987 and EN 13032-1:2004+A1:2012. The devices
should be calibrated annually to ensure accuracy.
When measuring light, the measuring sensor of the device should be placed at a number of positions where
the light is perceived to be brightest: this will give a good guide to the peak illuminance on the exhibit. The
measuring sensor’s surface should be placed on or very close to the surface of the exhibit being measured. It
should be oriented parallel to the exhibit (flat on the surface) as the measuring sensor is calibrated to
compensate for the varying angles that the light strikes the surface (cosine law). If the exhibit is not flat, the
sensor should be parallel to the most exposed or vulnerable surface.
If the room is lit with electric light only, it is sufficient to take one set of measurements to determine the peak
illuminance. The readings should be repeated and recorded periodically to take into account possible
variations of lighting conditions. Special lighting during cleaning works and similar shall also be measured and
taken into account in calculating the total annual luminous exposure.
If the room is lit with daylight, one set of measurements is not enough because light levels change with the
weather, time of day and season. To establish the annual exposure in day lit spaces the monitoring should be
done throughout one year to take into account the daily and seasonal variations. To do this readings have to
be taken at regular intervals during each day of the year and the readings properly evaluated to arrive at the
annual exposure expressed in lx·h per year. To make this process easier, automated data loggers are
available that can log the light levels from one or more light sensors over the year and provide an annual
figure.
The use of pre-existing data from external sources, such as meteorological offices, and modelling can be
adopted if an early estimate of annual exposure is required.
The effective damaging irradiance can be measured with an adapted irradiance sensor in consideration of the
definition of the relative damage action spectrum s(λ) . Another possibility is to calculate the effective
dm,rel
damaging irradiance by using the irradiance of the light source at the different wavelengths.
A qualitative evaluation of the total luminous exposure can also be obtained by disposable sensors such as
Blue Wool Standard cards or similar passive indicators or dosimeters, which fade or change their colour when
exposed to light in a pre-defined way. These allow a user-friendly and satisfactory indication of the light dose
received, expressed in terms of lx·h per year.
6.2 Measurement of UV radiation
The shorter wavelengths (UV and blue) have the highest energy and therefore cause the most damage to
exhibited materials. As UV light is not normally required for vision (except for the display of fluorescing
materials) it is advisable to filter this out or use low UV emitting light sources. To measure the level of UV light
falling on exhibits, special UV meters are needed. There are two types available: absolute UV meters and
relative UV meters. Some meters give both absolute and relative readings.
Absolute UV meters give a direct measurement in microwatt per square centimetre (μW/cm ) of the UV falling
on the measurement sensor. The relative UV meter was specially developed for museum use and measures
the proportion of UV radiation present in the light. It gives a reading in microwatts of UV per lumen of light
(μW/lm).
At present there is no standard for the spectral sensitivity of the measurement sensor used in relative UV
meters so meters from different manufacturers may be measuring slightly different regions of the UV
spectrum. The spectral sensitivity shall be verified to be suitable for museum use.
7 Exhibition lighting
7.1 General
The purpose of exhibition lighting is to present the exhibits in such a way that they may be studied and
appreciated. In most cases this means providing a lighting system that enables fine detail to be examined to
reveal the form, colour and texture of the exhibit. In some instances, the overall appearance of the display
may be more important than the visibility of the individual exhibits, in which case some form of “effects”
lighting may be required.
In general, exhibition lighting should provide a balance between a general wash of light and some form of
accent lighting. It will also require a balance between the luminance and colour of the exhibit and its
background. Exhibition lighting should also have good colour rendering properties and should be provided in
such a way that it is not intrusive or causes discomfort or disability glare. The techniques of exhibition lighting
may vary depending on the particular exhibits and whether they are freestanding or displayed in showcases.
The basic philosophy, however, will be the same.
7.2 Viewing conditions
Usually, we see exhibits because they contrast with their background or surroundings. This general
characteristic applies to everything we see, whether it is letters on a page or artefacts in a showcase. In
general, we are looking for the exhibits to be not only visible but also to attract attention, adding the element of
interest to visibility. Contrast should therefore be considered carefully when designing a display or a lighting
installation. Similarly, labels need to be produced where the text has a suitable size and contrast with the
background. Lighting then becomes a matter of providing the light on the labels that makes them as visible as
the exhibits without competing with them.
It is also necessary to consider the shape / form of the exhibits, and particularly any textural quality. Having
made the exhibit as a whole stand out, the detail should also be revealed. This will depend on the direction of
light falling onto the exhibit at the most appropriate angle. The correct contrast and direction of light flow are
therefore important in creating the best viewing conditions.
7.3 Visual adaptation
The eye reacts automatically to the brightness of a field of view adjusting rapidly for small changes in
brightness and more slowly to larger changes. The eye becomes adapted to the general brightness of a space
over a few minutes (for bright to dark) or several seconds (for dark to bright) and can then perceive exhibits
and surfaces lit over a reasonable range above and below that level, known as the adaptation level. Most
people have experienced this effect when moving from a brightly lit foyer into a dark cinema or theatre. In the
foyer all exhibits and surfaces can be seen well but when moving into the much darker space it is difficult to
find your way around. However, after a few minutes the eye adapts and all exhibits in the space become
visible.
In museums and galleries this can be a problem when moving from very brightly lit entrance halls into
exhibition spaces or when moving from a general gallery into one where extremely light sensitive exhibits,
such as works on paper and textiles, are displayed at very low light levels. Where possible the lighting
designer should d
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