Haze meter detects the transparent scattering characteristics of optical coatings.

This article introduces how a haze meter detects the transparency and scattering characteristics of optical coatings. Optical coatings are used in fields such as displays and packaging, where their transparency and scattered light affect product performance. Haze is the ratio of scattered light to total transmitted light. Haze meters measure this parameter using the integrating sphere principle and conduct tests in accordance with international standards. Factors such as particles within the coating and surface roughness can influence haze values, so sample preparation must be standardized. The measurement results can be used to optimize coating processes and quality control, with practical applications in industries such as displays and packaging. Current technology is advancing toward higher precision and online detection.

Overview

Optical coatings are widely used in displays, packaging, optical components, and functional films, and their transparency and scattering characteristics directly affect product visual quality and optical performance. Transparency typically refers to the proportion of light passing through the coating, while scattering characteristics describe how much light deviates from its original direction of propagation. Haze, the ratio of scattered light flux to transmitted light flux, is a key parameter for quantifying this property. The haze meter can accurately measure the haze and transmittance of the coating by simulating standard lighting and observation conditions, providing data support for coating process optimization and quality control.

Detection principle

Haze meters work on the integrating sphere principle. The parallel beam emitted by the light source is incident vertically to the coating sample, and the light passing through the sample consists of two parts: direct transmitted light and scattered transmitted light. The integrating sphere inside the instrument collects all the transmitted light and separates the direct light from the scattered light through a structure such as a light trap, and the detector measures its luminous flux separately. The haze value H can be calculated by the following formula:

H = (T_d / T_t) × 100%

Among them, T_dis the scattered transmitted light flux, T_tis the total transmitted light flux. At the same time, the instrument can directly measure the total transmittance T_t。 Domestic and international standards such as ASTM D1003 and ISO 14782 specify the geometric conditions, sample preparation and calibration procedures for testing to ensure consistency and comparability of measurement results.

Sample preparation

Coating haze is affected by a variety of factors. The internal particles, micropores, interfacial refractive index differences and surface roughness will cause light scattering. The haze of the substrate itself also needs to be taken into account in the analysis. Samples should be prepared to ensure clean, scratch-free surfaces and cut to fit the size of the instrument's sample window according to standards. For flexible coatings, they should be fixed flat to avoid the introduction of additional scattering into the folds. Before testing, the sample needs to be conditioned in a standard temperature and humidity environment to eliminate errors caused by environmental fluctuations.

Application scenarios

Haze detection has clear application value in many industrial fields. In the display industry, it is used to evaluate the visual clarity of anti-glare coatings; In the field of packaging, measure the transparent visual effect of the film; In optical manufacturing, it is related to the performance of functional coatings such as anti-reflection films. The measurement data not only provides the absolute values of haze and transmittance, but also the spectral dependence or trend of change at different angles of incidence, which can also reveal the uniformity and defect information of the coating structure.

Influencing factors	Typical effect on haze
Internal particles/micropores	Increased body scattering
Surface roughness	Increased surface scattering
Uniformity of coating thickness	Affects scattering consistency
The haze of the substrate itself	Contribute background scattering values

Operational precautions

To ensure measurement accuracy, the instrument needs to be calibrated regularly using a standard haze plate. The sample should be completely covered with the test hole to avoid ambient light leakage. For samples with high transmission or low haze, the number of measurements can be increased to average to improve the signal-to-noise ratio. The inner wall of the instrument integrating sphere should be kept intact with a high reflectivity coating to avoid contamination or aging. When not used for a long time, it should be stored and periodically verified according to the manufacturer's guidance.

Technology development trends

At present, haze detection technology is developing towards higher accuracy, multi-angle measurement and spectral resolution. Combined with image analysis technology, it is possible to visualize the haze distribution of the coating. In addition, the development of a high-speed haze measurement system suitable for online inspection to meet the needs of real-time quality control of production lines is also an important research direction. These advances will further enhance the dimension and efficiency of optical coating performance characterization.

Cited Literature

ASTM D1003-21, Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics.

ISO 14782:1999, Plastics — Determination of haze for transparent materials.

Optical Thin Film Technology, edited by Lu Jinjun et al.

Modern Optical Testing Technology, edited by Liu Jiarong et al.