Definition
Haze meter is an instrument used to quantify the optical properties of transparent or translucent materials, and its core measurement parameter is haze, which is the ratio of the luminous flux passing through the specimen deviating from the direction of the incident light to the total transmitted luminous flux, expressed as a percentage. Haze reflects the degree of visual blurring caused by scattering inside or on the surface of the material, and is a key indicator for evaluating optical transparency, uniformity and surface quality. This definition is based on the International Illumination Council and a number of domestic and foreign standards, such as the American Society for Testing and Materials standard D1003 and the Chinese national standard GB/T 2410.
Measurement principle
The working principle of a haze meter is based on the physical process of light scattering and transmission. The instrument typically consists of a standard light source, such as an A or C light source, which is collimated and directed vertically to the specimen surface. Light passing through the specimen enters the integrating sphere, which is coated with a highly reflective material on the inner wall to collect transmitted light in all directions. The detector measures the total transmitted light flux while passing through a movable trap or diaphragm to measure only the parallel transmitted light flux without scattering. Haze values are calculated by the following formula:
H = [ ( Ts - Tp ) / Tt ] × 100%
where H stands for haze, Tsis the transmittance corresponding to the scattered light flux, TpThe compensation value caused by the scattering of the instrument itself, Ttis the transmittance corresponding to the total transmitted light flux. During the measurement process, the stray light influence in the optical path is also deducted to ensure the accuracy of the results.
Measurement method
Haze measurement usually follows a standardized process, mainly divided into two types: direct method and compensation method. The direct method is suitable for uniform transmitted materials, and the total incident luminous flux without the specimen is measured during operation, and then the total transmitted luminous flux and scattered luminous flux after the specimen are put into the specimen, and the formula is substituted for calculation. The compensation method is used in the case where the specimen body may affect the optical path, and a blank specimen needs to be introduced for baseline calibration. Modern haze meters are mostly computer-controlled, capable of automatically completing multiple scans within seconds and outputting haze values and light transmittance. Before measuring, ensure that the surface of the specimen is clean and free of scratches, and adjust the ambient temperature to about 23 degrees Celsius and the humidity below 50% to reduce environmental disturbances.
Influencing factors
Haze measurements are influenced by a combination of factors. Internal factors include molecular structure, crystallinity, packing distribution, and bubble defects, which can cause volume scattering. Surface factors such as roughness, stains, or uneven coatings can enhance surface scattering. In terms of geometric conditions, the angle of incident light and the angle of view of the receiving field directly affect the acquisition range of scattered light, and the standard usually stipulates that the receiving angle is within 0.5 degrees. Among environmental factors, changes in temperature and humidity can lead to fluctuations in the material's refractive index or surface condensation, introducing measurement deviations. In addition, specimen thickness is also a key variable, as the haze value tends to increase nonlinearly as the thickness increases under the same material, so the specimen thickness needs to be indicated in the report.
Applications:
Haze meters have a wide range of uses in several non-medical industries. In the plastics and film industry, it is used to evaluate the optical uniformity of packaging films, display protectors, and glass mounting materials. In the optical glass and lens industry, haze metrics are used to measure lens clarity and image clarity. In the field of new energy, such as solar photovoltaic module packaging materials, low haze can ensure light transmittance to improve power generation efficiency. In the food and beverage packaging industry, the haze values of plastic bottles and containers need to comply with food safety packaging standards to avoid visual defects. In the coatings and inks industry, surface gloss and coverage are verified by measuring coating haze. In the field of architectural and automotive glass, haze control is an important part of ensuring clear vision and traffic safety.
Selection guide
The following points should be considered when choosing a haze meter. First, the characteristics of the material being measured are clarified, including the range of light transmittance, thickness, and the presence of color or texture. Secondly, pay attention to the type of light source, the common ones are A light source and D65 light source, and the haze value may be different under different light sources, which should be matched according to the application standard. Third, check the integrating sphere diameter and receiving optical path design, and select a model that can effectively suppress stray light and is suitable for sample types. Fourth, considering the resolution and repeatability of the instrument, the repeatability of the haze measurement is usually required to be less than 0.05%. Fifth, evaluate the ease of operation, including the presence of automatic calibration functions, data output interfaces, and software compatibility. Finally, confirm that the equipment complies with relevant domestic and international standards, such as ASTM D1003, ISO 14782, or GB/T 2410, and has traceable certifications. It is recommended to validate the instrument using standard haze sheets before formal procurement to ensure that its actual performance meets the testing needs.