1Laura Bellia, 1,2Alessia Pedace, 1Francesca Fragliasso, 1Emanuela Stefanizzi
1Dep. Industrial Engineering, University of Naples Federico II, [email protected], [email protected], [email protected]
2Dep. of Energy, Information Engineering and Mathematical Models, University of Palermo, [email protected]
1. Introduction
In recent years new interior design projects frequently feature walls painted with intense colours, both in residential and tertiary sector applications. Usually the choice of a given walls' colour is made basing on esthetical reasons, or marketing ones in case of tertiary applications. For example it may be decided to paint the walls of a new chain shop with the brand's trademark colour.
However this choice should be also performed according to that of the lighting system since it may have an impact on users' comfort. Indeed a given combination of light sources with a certain spectral power distribution (SPD) with a specific walls' colour may determine an unpleasant environment, visual discomfort or even affect mood and performances. Indeed several studies on the effect of walls' colour on performance, mood, etc. were carried out in the past [1,2,3,4].
The research project reported in this paper aims at analyzing the effects of the combination of different walls' colours and light scenes with different correlated colour temperatures (CCTs) on the spectral distribution of the light that hits users' eyes. Since this study represents the first step of a wider research project only electric light was analyzed, however future studies will also focus on daylight. The CIECAM02 colour appearance model [5] was also applied to investigate if and how the colour attributes of the walls vary when changing the light scene and the results obtained are reported in this paper.
Moreover a previous research by the authors [6] demonstrated that there is a good correlation between hue values calculated with the CIECAM02 colour appearance model and hue values reported by subjects. Therefore the application of this model may also provide indications about people's perception of the environment.
Future tests will be performed to fully investigate users' perception and to further verify the correlation with the CIECAM02 model. It is important to highlight that the CIECAM02 colour appearance model has been criticized by many researchers [7] but so far no modifications or new models were proposed; therefore in this paper the CIECAM02 will be applied since there is no better option.
2. Method
This study was carried out in a test room of the Photometry and Lighting Laboratory of the Department of Industrial Engineering of the University of Naples Federico II (Italy). The spectral reflectance of one of the test room's walls (the one in front of the desk) was changed by applying cardboards on it.
Figure 1 shows the test room's measured plan, the room's window was totally obscured during the study with a panel.
Fig. 1 - Test room measured plan.
The test room is equipped with LED luminaires controlled by a DALI system that allows to change light's intensity, CCT and also to save different light scenes once they are set up. Luminaires' technical specifications and photometry (as provided by the manufacturer) are reported in Figure 2.
Fig. 2 - Luminaires' technical specifications and photometry.
Four light scenes were set up with different CCTs: 2700 K, 3000 K, 4500 K and 6500 K. All light scenes determine an illuminance value equal to 300 lx on the desk.
Table 1 reports for each of them colour rendering index (CRI) values, CCTs and
∆uv values all detected with a Konica Minolta CS2000 spectroradiometer.
Light scene Measured CRI Measured CCT [K] ∆uv
2700 K 90 2626 - 0.0016
3000 K 92 3008 - 0.0035
4500 K 91 4561 - 0.0036
6500 K 90 6555 - 0.0038
Tab. 1 – Light scenes' characteristics
Figures 3a,b,c report the spectral reflectances, measured with a Konica Minolta CM-2600d spectrophotometer, of the test room's surfaces and furniture and of the front wall with the coloured cardboards on. Light scenes' normalized SPDs are also reported.
a)
b)
c)
Fig. 3a,b,c - Spectral reflectances of the test room's surfaces and furniture and of the front wall with the coloured cardboards on, light scenes' normalized SPDs.
Figure 4 shows photos of the front wall with the red cardboards on lit by the different light scenes.
Fig. 4 - Photos of the front wall with the red cardboards on lit by the different light scenes.
To apply the CIECAM02 model the adapting luminance (cd/m2) was calculated by dividing for π the illuminance detected by placing the spectroradiometer in the same position of the head of a person seated at the desk (at an height of 1.20 m, see Figure 4). The relative luminance of the surround was considered as average. The reference white is an A4 paper sheet placed on the front wall, its tristimulus values were measured with each light scene and coloured cardboard.
Tristimulus values of the coloured cardboards were also detected under each light scene.
3. Results
In the following graphs the results related to the front wall without the coloured cardboards will be referred to as "Base case". Figures 5a,b,c respectively show hue, chroma and lightness values calculated with the CIECAM02 model for each coloured cardboard under all light scenes.
a)
b)
c)
Fig. 5a,b,c - CIECAM02' s hue, chroma and lightness values calculated for each coloured cardboard and light scene.
It is interesting to observe that the greatest variation in hue angle values is found for the base case and with pale blue and white cardboards. Red and orange ones show almost null hue differences when changing the light scene whereas for violet cardboards they increase a little.
On the contrary, referring to chroma values, violet, orange and red cardboards are the ones showing the greatest differences. Orange and red cardboards are also the ones for which the greatest lightness variation was calculated, whereas for the other cardboards there is almost no difference when changing the light scene.
In addition, Table 2 reports colour differences calculated for each front wall's colour using the following equations and taking as reference the values related to the 2700 K light scene.
∆L = L2700K - Lx (Eq. 1)
∆H = H2700K - Hx (Eq. 2)
∆C = C2700K - Cx (Eq. 3)
Tab. 2 – Analysis of chromatic differences
It is interesting to highlight that red and orange cardboards are the only ones for which there is both a great difference in chroma and lightness values. Moreover the greatest colour differences are always those calculated between the 2700 K and 6500 K light scenes. Another interesting result is the great hue variation calculated for the base case. Since it is an almost neutral colour (see Figure 3b) this difference depends on the light scene's variation, whereas in the other cases differences are due to the combination of the cardboards' spectral reflectances and light scenes' characteristics.
4. Discussion and Conclusions
The results reported in this paper highlighted that there are significant variations in the colour attributes of the front wall with the coloured cardboards on when changing the light scene.
To understand if there are also strong differences in people's perception of this environment tests are required. A previous study [6] demonstrated that there is a good correlation between CIECAM02's hue values and hue perceived by people, but to confirm this finding further tests are required.
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