Can LEDs help with art conservation? – Impact of different light spectra on paint pigment degradation

The impact of the spectral composition of light on the discoloration of paint pigments has been investigated for the case of lead chromate sulfate, an unstable yellow pigment used by Vincent van Gogh and other painters. With LEDification, museum lighting is moving from using halogen to LED lamps. LED light sources have a significantly different spectral composition than halogen lamps. To understand the impact of these differences on pigment stability, the wavelength dependence of pigment discoloration was determined. Contrary to the expectation that lower wavelength photons induce more damage than higher wavelength ones, UV (394 nm), blue, and cyan light all lead to similar levels of discoloration of a pigment for the same level of radiant power. By understanding this wavelength dependence, it becomes possible to create white light LED lamps with a spectral composition tuned to minimize the degradation effect. An existing LED solution with a modified emission indeed resulted in 30% less color change in the experiment than halogen. Furthermore, a method is proposed to optimize the LED spectra by tuning to the properties of each specific artifact. Simulations show that this can reduce the damage of the light source by 45% in specific cases.本研究针对铬酸硫酸铅（lead chromate sulfate）这一由文森特·梵高及其他画家曾使用的不稳定黄色颜料，探究了光的光谱组成对涂料颜料褪色的影响。随着博物馆照明向LED化转型，当前正逐步从卤钨灯切换为LED灯具。相较于卤钨灯，LED光源的光谱组成存在显著差异。为明确此类光谱差异对颜料稳定性的影响，本研究测定了颜料褪色的波长依赖性。与"低波长光子相较于高波长光子会造成更严重损伤"的固有预期相悖，在相同辐射功率条件下，紫外线（394 nm）、蓝光及青光对该颜料的褪色程度均相近。明晰这一波长依赖性后，即可研发出光谱组成可调节的白光LED灯具，以最大限度抑制颜料的光致降解。实验中，一款经过发射光谱优化的现有LED照明方案，其引发的颜色变化量较卤钨灯低30%。此外，本研究提出了一种可针对每件特定文物的属性调节光谱的LED光谱优化方法。模拟结果表明，在特定场景下，该方法可将光源造成的损伤降低45%。