# Advancing Sustainable Textile Metrology: Reflectivity Measurement with Controlled Light Sources
## 1 Introduction  
Reflective textile products are widely used in industries such as road safety, sportswear, and specialized uniforms [1]. Measuring their reflectivity is essential for determining their effectiveness under various lighting conditions [2, 3]. Traditional reflective threads are typically made from rigid polymer or metallized materials [4] and are primarily used in woven macrostructures, as the weaving process facilitates their integration into the fabric [5]. As a result, woven reflective textiles have limitations like low flexibility, limited comfort, and reduced drapeability [6, 7]. These limitations create the need for alternative structures that combine high reflectivity with improved flexibility and comfort. Fabrics with a knitted macrostructure offer precisely this possibility. There are several methods for evaluating the reflective properties of flexible textile products. Spectrophotometric analysis of light reflected from a textile macrostructure is a method used to determine the color characteristics and optical properties of textile materials [8]. This method allows for measuring the amount of light reflected from the textile surface at different wavelengths. A key aspect of spectrophotometric analysis is to measure spectral reflectance, determining what percentage of the incident light is reflected by the textile in the visible spectrum (400-700 nm) [9; 10]. This is crucial for assessing the perceived color and brightness of the material. Based on this, color parameters are also evaluated by calculating coordinates in different color spaces (e.g., CIELAB), allowing for an objective assessment of color [11; 12]. In practice, spectrophotometry enables comparisons (e.g., of production batches) with reference samples, ensuring consistency in the color and appearance of the textile product [13]. The advantages of the spectrophotometric analysis include high accuracy and repeatability, making it widely used [14]. It provides objective and quantitative data on the optical properties of the textile macrostructure [15]. Additionally, the method is non-destructive, which is important for preserving the integrity of valuable or delicate fabrics. The disadvantages of the method are related to the high cost of spectrophotometers, as well as the expense of replacing reference standards [13], which makes the method inaccessible for manufacturers or laboratories with limited budgets. The spectrophotometer requires regular calibration and a controlled environment to ensure accurate measurements [15; 16], as well as specialized training for operation. Goniophotometry is a method for measuring the reflective and light distribution characteristics of materials, including textiles with reflective properties [17]. Unlike traditional photometric techniques that measure the total reflected light, a goniophotometer records the intensity of light at different angles [18]. In addition to a light source that illuminates the sample at a controlled angle and a sensor for measuring the intensity of the reflected or scattered light, the system is also equipped with a rotational mechanism to rotate either the sample or the sensor to measure reflection at different angles [19]. It is particularly useful for studying retroreflective and reflective materials, such as textiles with reflective threads, road signs, and lighting fixtures [18; 20]. However, its use requires expensive equipment and specialized expertise for setup and data analysis, making it impractical for small laboratories. The Photometric method, using a lux meter, is a simple and accessible way to measure the reflective properties of textile materials. This method is based on measuring the intensity of reflected light using a device (lux meter) that records illumination in lux (lx) [21]. The intensity of the reflected light from a sample containing reflective threads is compared to a control sample (a textile without reflective threads) to determine the efficiency of the reflective material [22].