Wood discoloration patterns depending on the light source

Abstract

The wood photodegradation, including discolouration caused by exposure to UV and solar radiation, has been intensively studied, while the effect of artificial lighting on wood has been little investigated. In the present study, the effect of three types of artificial light sources (LED, incandescent, and fluorescent lamps) on the colour changes of wood was evaluated. LEDs with high (6500 K) and low (3000 K) correlated colour temperature were employed in the experiments. Wood colour was assessed by spectrophotometric measurements of reflectance spectra, which were converted into colour parameters of the CIELAB colour system. The total discolouration as well as the changes in colour lightness, chroma (saturation), and hue were evaluated for two hardwood species (birch, oak) and two softwood species (spruce, pine - sapwood and heartwood) depending on the irradiation dose. Visually perceivable changes in colour of all woods were observed already at relatively low irradiation doses, indicating a high sensitivity of the wood to radiation emitted by artificial light sources. Comparing the softwoods and hardwoods included in the study, the latter proved to be more resistant to discolouration caused by the tested light sources. Overall, greater colour changes in long-term exposure were caused by incandescent and fluorescent lamps, although more rapid discolouration developed in the early stage irradiation with LEDs. A substantial difference between the effect of the tested LEDs was only observed in the initial phase, when the cool LED (6500 K) caused more discolouration. The changes in the colour parameters were complex and varying in directions, including a reversal with the accumulation of the irradiation dose, indicating that the exposure to artificial light sources resulted in continuous alteration in the shade of the wood colour.

Aging of Wood for Musical Instruments: Analysis of Changes in Color, Surface Morphology, Chemical, and Physical-Acoustical Properties during UV and Thermal Exposure

“…The spruce darkened more compared to the sycamore maple samples, recording a total color variation of around 15 when compared to the sycamore maple, whose total color variation was around 10, as can be seen in Table 1 . The results obtained are in agreement with those reported by [ 21 , 39 , 40 ], where the change in color for spruce was the largest among all the investigated species. Some researchers [ 10 ] found that the sycamore maple that was subjected to a long simulated natural aging process indoors suffered from a dramatic decrease in brightness after 4–5 months of exposure.…”

“…Due to different light spectrums, the photodegradation processes of indoor wood are not the same as those for outdoor wood. The studies carried out by artificial aging procedures on different wood species have shown that the color changes are rapid in the first 12 h of exposure for hardwoods and for the first 24 h for softwoods [ 9 , 20 , 21 , 22 ]. A continuation of the exposure time beyond these limits has shown a decrease in the fading speed.…”

Light-Induced Colour Changes in Wood Surfaces in Indoor Conditions Determined by an Artificial Accelerated Test: Influence of Wood Species and Coating Materials

“…The result is, therefore, that the light-induced colour changes in wood surfaces are significantly influenced by the wood species due to the differences in their chemical composition, as proven by comparative research on more than two different species [1,[22][23][24]. Colour changes also depend on the type of light (natural/artificial), spectral range (wavelengths), type of light source, exposure conditions and duration [25][26][27]. Accordingly, data from different research publications are often difficult to compare.…”

“…More studies have focused on the exposure of wood in outdoor conditions where UV radiation acts in conjunction with rainwater [2,32,45], while the topic of light-induced colour changes in indoor conditions by the natural light passing through the window glass [1,22,23,36] or light from artificial sources [26,27] has been less addressed, especially for clear-coated wood with natural aspect [46,48].…”

Tensor decomposition for painting analysis. Part 2: spatio-temporal simulation

“…A wide range of materials manifests light-induced appearance changes. To name only a few: wood [1], paper [2], dyed textiles [3], pigments [4]. For this reason, it is of general interest to create models that are able to predict future degradation as a function of light exposure.…”