Embed Size (px)
Citation preview
Zumtobel basic knowledge
Damage causedby optical radiation
Ralf Müller, Dornbirn | AT
1 Changes in colour caused by optical radiation 4
2 Measuring device 7
3 Typical values and interpretations 9
Zumtobel basic knowledgeDamage caused by optical radiation
The lighting-related change in colour of materials typically displayed in museums is a visible fi nal product of the photochemical effects of optical radiation, which can be described by effective radiometric quantities. The most important factors for assessing the potential risk of optical radiation are explained below. The potential risk posed by a lighting situ-ation depends on the light source as well as on the material of the illumi-nated object.The overall context is described in the CIE 157:2004 technical report and in the 2006 “Museum Lighting” report of the "Fördergemeinschaft Gutes Licht" association.
Effective irradiance Edm, which causes damage to an object, is defi ned according to the formula:
With spectral irradiance Eeλ, relative spectral sensitivity sdm,rel(λ) and wavelength dλ.
Hence, spectral irradiance describes the amount of energy per wave-length emitted by a light source. As spectral radiation distribution differs between lamp types, this is precisely the decisive factor that has to be taken into account when selecting light sources for museum lighting. This is illustrated in the following two diagrams by the areas below the curves of spectral radiation distribution and of relative spectral sensitivity coloured in orange.
1 Changes in colour caused by optical radiation
XENO QT 12 100 W dimmed down to 30 % with UV/IR fi lter
ARCOS 3 TunableWhite 2 700 K
5
Relative spectral sensitivity is described according to the formula:
With material constant b.
The table below gives a summary of the material-dependent parameters for a variety of materials (according to CIE 157:2004):
Material Threshold radiation Material constant Hs,dm [Wh/m²] b
Newspaper 5 0.0380Rag paper 1 200 0.0125Oil colours on canvas 850 0.0115Textile materials 290 0.0100Water colours on paper rag 175 0.0115
Threshold radiation Hs,dm describes the amount of radiation energy that must act on an object until a visible change in the object's colour occurs. The values given in the table above are based on the investigations car-ried out by Aydinli at the Berlin Institute of Technology in 1983. The val-ues were obtained from radiation studies and comparisons of non-irradi-ated and irradiated materials.
Relative spectral sensitivity sdm,rel(λ), which is decisive for theobject's colour, can be obtained via an exponential function. The normal-ised value of the function is 1 at a wavelength of 300 nm, as radiation below this wavelength limit very rarely occurs in museum lighting involv-ing daylight or artifi cial lighting. The sequence of the function is described by material constant b, which determines a material's specifi c spectral absorptance. These values are also based on the investigations carried out by Aydinli at the Berlin Institute of Technology in 1983.The individual relative spectral sensitivity levels are displayed in the dia-gram.
It shows that all materials typical of sensitive museum objects, with the exception of newspapers, present a similar sequence of relative spectral sensitivity. To simplify things, we might say that the function of the mate-rials follows a material constant value of b=0.012.
Newspaper
Rag paper
Oil colours on canvas (as water colours)
Textiles
Water colours on rag paper
The potential damage Pdm is the fi xed proportion between effective irra-diance Edm and illuminance E and applies to one lighting situation and one object or material:
The potential damage is not connected to the illuminance level, which means that the potential damage remains constant at different illumi-nance levels. This makes it a factor well suited to describe the potential risk posed by a lighting situation.
These factors may be used to defi ne the threshold exposure or critical radiation time ts, after which there is a risk of visible damage:
With material-dependent threshold radiation Hs,dm.
In summary, the following can be said:The illuminance level alone is not suitable for assessing the levels of protection or damage to objects through optical radiation. It is neces-sary to know the effective irradiance level which describes the poten-tial damage in combination with the level of illuminance.
72 Measuring device
As described above, the most signifi cant factor for assessing the poten-tial risk for damage due to optical radiation is the level of effective irradi-ance. However, the measuring devices usually available in museums today are only able to measure illuminance levels.For a signifi cant assessment to be made, the levels of both Edm and E should be measured at the same time. For this purpose, it became nec-essary to develop a new measuring head that is able to make spectral measurements, once evaluated in correspondence with v(λ) [lx] and once evaluated in correspondence with the relative spectral sensitivity sdm,rel(λ).This is exactly what the new measuring device developed by the Berlin Institute of Technology in collaboration with Zumtobel does.
The measuring head of the measuring device is fi tted with 4 sensors. 1 sensor (white) for illuminance (lux), 3 sensors (reddish, bluish, greenish) for measuring the irradiance level in specifi c wavelength ranges. Corre-sponding to an exponential function with a material constant of b=0.012.
The evaluation unit has a built-in display showing three values.
E Illuminance given in lux [lx]Edm Effective irradiance given in watts per square metre [W/m²]Pdm The potential damage is calculated from the two previously stated (measured) values, given in milliwatts per lux and square metre [mW/lx m²] or milliwatts per lumen [mW/lm].
Wavelength [nm]R
el. s
ensi
tivity
OperationThe device is switched on by pressing the on/off button.After switching on, the three values will be displayed after just a few seconds. The measuring device measures and displays the current val-ues on an ongoing basis. The arrow buttons on the housing have no function and can be disregarded.For operation, a standard 9 V monobloc battery is used, which is insert-ed into the battery compartment at the back of the device.
PrecisionThe objective of the measuring device is to assess the risk posed by the lighting situation or the risk of damage through light, i.e. radiation in the optically visible range. Measurement precision has a tolerance of ±10 %. This is a measuring device of quality class C according to DIN 5032 Part 7.
9
Potential damageThe potential damage can be defi nitely attributed by measurement of the spectral radiation distribution and evaluation depending on the relative spectral sensitivity typical of a luminaire. The table below shows the val-ues applying to luminaires from our product range.
Expressed in simplifi ed terms, this means:In case of LEDs, the potential damage decreases with declining colour temperature.
3 Typical values and interpretations
Colour temperatureLuminaire 2 700 K 3 000 K 4 000 K 5 000 K 6 500 K
Potential damage Pdm [mW/lm] 1)
ARCOS 3 TunableWhite 0.14 0.15 0.17 0.23
ARCOS 2 LED 12 W (15°) 0.15
ARCOS 2 LED 12 W (25°) 0.16
ARCOS 2 xpert 22 W CRI >90 2) 0.16
SUPERSYSTEM 2.5 W CRI >90 0.14
SUPERSYSTEM 2.5 W CRI >80 0.16
MICROTOOLS 1.1 W CRI >80 0.15
VIVO L LED Ess+ CRI >90 0.16
PANOS infi nity CRI >80 0.15 0.19
Xicato XSM Artist 0.15 0.16 0.21
Standard lighting A 0.22
Standard lighting D65 0.61
1) Determined using a material constant of b=0.012, normalised to 100 lx2) ARCOS 2 Xpert fi tted with Philips Luxeon S LED module from July 2013
Threshold exposureThe information provided in the table and diagram below shall give you a sense of how threshold exposure ts will be reduced or extended due to changes in the levels of potential damage or illuminance.
The threshold exposure levels show that the fi gures are correlated with simple proportions:
• Doubling the potential damage will reduce threshold exposure by half• Doubling the illuminance level will reduce threshold exposure by half
The diagram below shows the curves of these correlations for rag paper.
Material: Rag paper
Illuminance E [lx]
50 100 150 200 250 300
Pdm Threshold exposure [mW/lm] ts [h]
0.10 240 000 120 000 80 000 60 000 48 000 40 000
0.11 218 182 109 091 72 727 54 546 43 636 36 364
0.12 200 000 100 000 66 667 50 000 40 000 33 334
0.13 184 615 92 308 61 538 46 154 36 923 30 769
0.14 171 429 85 715 57 143 42 857 34 286 28 572
0.15 160 000 80 000 53 333 40 000 32 000 26 667
0.16 150 000 75 000 50 000 37 500 30 000 25 000
0.17 141 176 70 588 47 059 35 294 28 235 23 530
0.18 133 333 66 667 44 444 33 333 26 667 22 222
0.20 120 000 60 000 40 000 30 000 24 000 20 000
0.23 104 348 52 174 34 783 26 087 20 870 17 392
0.27 88 889 44 445 29 630 22 222 17 778 14 815
0.54 44 444 22 222 14 815 11 111 8 889 7 408
11
Colour rendering index vs. potential damageAnother important information component can be derived from the cor-relations of the laws of thermal radiation. The higher the colour rendering index of a light source, the closer its potential damage to that of stand-ardised lighting A (temperature spotlight, halogen spotlight). The dia-grams below show the spectral radiation distribution levels of various LED luminaires / LED modules at approximately the same colour temper-atures. The potential damage level and colour rendering index are indi-cated as well.
Colour temperature index CCT 2 700 K
Colour temperature index CCT 3 000 K
Colour temperature index CCT 4 000 K
United KingdomZumtobel Lighting Ltd.Chiltern ParkChiltern Hill, Chalfont St. PeterBuckinghamshire SL9 9FGT +44/(0)1753 482 650F +44/(0)1753 480 [email protected] zumtobel.co.uk
USA and CanadaZumtobel Lighting Inc.17-09 Zink Place, Unit 7Fair Lawn, NJ 074103300 Route 9WHighland, NY 12528T +1/(0)845/691 6262F +1/(0)845/691 [email protected]
Australia and New ZealandZumtobel Lighting Pty Ltd333 Pacific HighwayNorth Sydney, NSW 2060T +61/(2)8913 5000F +61/(2)8913 [email protected]
ChinaZumtobel Lighting China Shanghai officeRoom 101, No 192 YIHONG Technology ParkTianlin Road, Xuhui DistrictShanghai City, 200233, P.R. ChinaT +86/(21) 6375 6262F +86/(21) 6375 [email protected]
Hong KongZumtobel Lighting Hong KongUnit 4319-20, Level 43,Tower 1, Metroplaza, 223 Hing Fong Road, Kwai Fong, N.T.T +852/(0)2503 0466F +852/(0)2503 [email protected]
IndiaZumtobel Lighting GmbHA 274, 1st Floor,Defence Colony,110024 New DelhiT +91/98 102 19 [email protected]
SingaporeZumtobel Lighting Southeast Asia5 Kaki Bukit Crescent, #04-02 Koyotech Building416238 SingaporeT +65 6844 5800F +65 6745 [email protected]
United Arab EmiratesZumtobel Lighting GmbH (Branch)Dubai Airport Free Zone, Building 6W, B Block, 233 PO Box 54302 DubaiT +971/(0)4 299 3530F +971/(0)4 299 [email protected]
Romania Zumtobel Lighting Romania SRLTipografilor 11–15, S-Park Office, Wing A1-A2013714 BucharestT +40 312253801F +40 [email protected] zumtobel.com
Hungary Zumtobel Lighting KftVáci út 491134 BudapestT +36/(1) 35 00 828F +36/(1) 35 00 [email protected] zumtobel.hu
Croatia, Bosnia and Herzegovina Zumtobel Licht d.o.o.Radnička cesta 80 – Zagrebtower10000 ZagrebT +385/(1) 64 04 080F +385/(1) 64 04 [email protected] [email protected]
Serbia Zumtobel Licht d.o.o.Karadjordjeva 2-4Beton Hala11000 Belgrade T +381/(0)11 65 57 657F +381/(0)11 65 57 [email protected]
Czech Republic Zumtobel Lighting s.r.o.Jankovcova 2Praha 7170 00 PrahaT +420/(2) 66 782 200F +420/(2) 66 782 [email protected]
Slovak RepublicZumtobel Lighting s.r.o Vlčie Hrdlo 1, 824 12 [email protected]
PolandZumtobel Licht GmbH Sp.z.o.o.Platinium IIIul. Wołoska 9a02-583 WarszawaT +48/(22) 856 74 31F +48/(22) 856 74 [email protected]
SloveniaZumtobel Licht d.o.o.Štukljeva cesta 461000 LjubljanaT +386/(1) 5609 820F +386/(1) 5609 [email protected]
RussiaZumtobel Lighting GmbHOfficial Representative OfficeSkakovaya Str. 17Bld. No 1, Office 1104125040 MoscowT +7/(495) 945 36 33F +7/(495) 945 16 [email protected]
NorwayZumtobel BelysningHoffsveien 4Postboks 1025 Hoff0218 OsloT +47 22 06 50 50F +47 22 06 50 [email protected]
SwedenZumtobel BelysningBirger Jarlsgatan 57113 56 StockholmT +46 8 26 26 50F +46 8 26 56 [email protected]
DenmarkZumtobel BelysningIndiavej 12100 KøbenhavnT +45 35 43 70 00F +45 35 43 54 [email protected]
HeadquartersZumtobel Lighting GmbH Schweizer Strasse 30Postfach 726851 Dornbirn, AUSTRIAT +43/(0)5572/390-0F +43/(0)5572/22 [email protected]
Zumtobel Licht GmbH Grevenmarschstrasse 74-7832657 Lemgo, GERMANYT +49/(0)5261 212-0F +49/(0)5261 [email protected]
zumtobel.com
zumtobel.com
