# Advancing Sustainable Textile Metrology: Reflectivity Measurement with Controlled Light Sources
## 1 Introduction
However, this can be a limitation of the method, as a control sample with the same macrostructure, composition, and characteristics as the specimen containing reflective threads is not always available. The accuracy of the method depends on the measurement angle and ambient light conditions, and, in all cases, it is inferior to methods using a spectrophotometer or goniophotometer [19; 23]. Nevertheless, the method has the important advantage of being efficient and quick for use in both laboratory and industrial settings. The equipment is affordable and easy to operate. Standardized tests are part of international standards that define methods for measuring the reflective properties of textiles. They ensure comparable and accurate measurements by establishing methodologies for evaluating reflectivity. Tests conducted according to specific standards are critical for quality control in the production of protective clothing, sports equipment, and other materials with reflective properties [24]. The main international standards in this field are the following:  
* ISO 20471:2013--Defines the requirements for high-visibility clothing used in work and road safety [25]. * ASTM E808/E809--Describes methods for measuring the retroreflection of materials using a goniophotometer [26]. * EN 471--European standard for high-visibility protective clothing, including tests for reflectivity [27]. EN 471:2003 has been superseded by ISO 20471:2013 [25], but it is good to be known for historical comparisons. The primary testing methods in standardized tests include goniophotometric analysis and spectrophotometry. Additional tests assess the durability of reflective textiles after washing [28], abrasion [29], and exposure to environmental conditions [30]. Standardized tests are essential for ensuring the reliability and effectiveness of reflective textile materials in real-world applications. Measuring the reflectivity of textiles using spectrophotometry and goniophotometric analysis is expensive and challenging for small laboratories, as well as for small and medium-sized companies aiming to produce fabrics, clothing, or wearable devices with reflective properties [31]. Standardized tests are also primarily based on the use of spectrophotometers and goniophotometers. The most accessible method is the use of a lux meter [32], but it has one major drawback--the reference sample. It is possible that the analysis of a textile product's reflectivity (fabric) may need to be conducted in the absence of a reference sample with the same macrostructure and characteristics but without reflective elements (threads, fibers, nanoparticles). This study introduces a method for objectively measuring the reflectivity of flexible textiles using a controlled lighting environment. The methodology employs a light booth with multiple illuminants and a lux meter to assess the reflective properties of knitted textile samples. The proposed approach provides both qualitative and quantitative evaluation of reflectivity, allowing for a systematic comparison of different knitted macrostructures. By considering the influence of fabric design (knitted pattern) on reflectivity, this study supports the development of sustainable, high-performance reflective textiles for protective and wearable applications.