An optical transmittance change test report documents how the light transmission performance of transparent and translucent materials varies after exposure to environmental, thermal, or UV conditioning. This article explains the test principle, applicable standards, sample requirements, measurement methods, and typical applications of optical transmittance change testing performed by accredited third-party laboratories. Understanding this report helps manufacturers in the optics, display, automotive, and photovoltaic industries verify material stability and product durability.
Technical Overview
Optical transmittance change testing evaluates the ability of a transparent material to maintain its light transmission characteristics after being subjected to specified conditioning treatments, such as high temperature, high humidity, thermal cycling, ultraviolet (UV) irradiation, or abrasion. The test compares the luminous transmittance of a sample measured before and after treatment, and the resulting change value is expressed as a percentage. A professional optical transmittance change test report provides objective evidence of material stability, which is essential for product qualification, incoming material inspection, reliability validation, and regulatory compliance.
Transmittance is defined as the ratio of luminous flux passing through a specimen to the luminous flux incident on the specimen. In practice, measurements are typically performed over the visible spectrum (380 nm to 780 nm) or at a specified reference wavelength, such as 550 nm, using a UV-Visible spectrophotometer equipped with an integrating sphere. The report records the initial transmittance, the post-treatment transmittance, and the calculated change, allowing engineers to assess whether the material meets the acceptance criteria defined in product specifications or international standards.
Testing Samples
Optical Glass and Architectural Glazing
Clear glass, tempered glass, laminated glass, coated low-E glass, and patterned glass used in buildings, vehicles, and optical instruments. These samples are typically cut into standard specimens, such as 50 mm × 50 mm squares, with surfaces cleaned and free of defects before measurement.
Polymer Films and Sheets
Transparent plastic materials including PET, PC, PMMA, PVC, TPU, and optical adhesive films. These materials are widely used in display modules, protective films, solar encapsulants, and flexible electronics, where long-term optical stability is critical.
Coated and Functional Substrates
Specimens with anti-reflection (AR) coatings, hard coatings, indium tin oxide (ITO) conductive layers, or hydrophobic coatings. Because coatings may degrade under heat, humidity, or UV exposure, transmittance change testing is used to verify coating durability.
Display Cover and Touch Panel Materials
Cover glass, cover lens materials, and touch sensor substrates for smartphones, tablets, automotive displays, and industrial HMI panels. These components must retain high transmittance and low haze after environmental stress testing.
Testing Items
A comprehensive optical transmittance change test report typically covers the following measurement items:
- Initial luminous transmittance (T1) measured before any conditioning treatment.
- Post-treatment luminous transmittance (T2) measured after the specified environmental or durability test.
- Transmittance change rate, calculated as ΔT = (T2 − T1) / T1 × 100%, reported as an absolute or relative percentage.
- Total transmittance and parallel transmittance for materials where directional light transmission matters.
- Haze value and haze change, measured in accordance with ASTM D1003 or ISO 14782, to quantify light scattering caused by surface degradation or bulk clouding.
- Spectral transmittance curves across the visible wavelength range, providing full characterization of optical behavior.
- Optional items such as solar transmittance per ISO 9050, color coordinates, and yellowness index change after aging.
Testing Methods
The test sequence consists of baseline measurement, environmental conditioning, post-treatment measurement, and data analysis. All measurements should be performed by qualified personnel in accredited third-party laboratories using calibrated instruments, and the test report must clearly state the applied standards, equipment, conditions, and results.
Measurement Standards and Instrumentation
Luminous transmittance is commonly measured according to ASTM D1003, ISO 13468-1, ISO 13468-2, GB/T 2410, or JIS K 7361-1, depending on the material type and market requirements. For glazing products, ISO 9050 and the corresponding EN and GB standards apply. A double-beam UV-Visible spectrophotometer with an integrating sphere is used to capture both regular and diffuse transmitted light, ensuring accurate results for slightly hazy or scattering specimens. For solar transmittance, ASTM E424 may be referenced.
Conditioning and Durability Treatments
Transmittance change is evaluated after one or more conditioning procedures selected according to the intended application:
- Thermal aging: high-temperature storage, for example 85 °C or 120 °C for a defined duration, to simulate long-term heat exposure.
- Damp heat testing: 85 °C / 85% relative humidity, widely used for display and photovoltaic materials.
- Thermal cycling: repeated transitions between temperature extremes to induce stress and delamination.
- UV or xenon arc weathering: light exposure per ISO 4892-2, ISO 4892-3, or ASTM G155 to replicate sunlight degradation.
- Abrasion resistance testing: surface rubbing or falling sand methods, after which transmittance loss and haze increase are assessed.
Calculation and Acceptance Criteria
After conditioning, specimens are conditioned to equilibrium in a standard laboratory atmosphere and remeasured under identical instrument settings. The transmittance change is calculated and compared with the acceptance limit specified by the client or the applicable product standard. Typical acceptance criteria for high-quality optical materials require the absolute transmittance change to remain within a few percentage points, while display-grade components often demand even tighter limits. The report includes specimen photographs, spectral curves, and a clear pass or fail conclusion against the specified criteria.
Applications
Optical transmittance change testing supports quality control and certification across many industries:
- Display and touch panel manufacturing, where cover materials and optical films must maintain transmittance after thermal, humidity, and UV reliability tests.
- Automotive glazing and interior displays, where laminated windshields and instrument panel materials require verified optical durability.
- Photovoltaic modules, where encapsulant films and front sheets must retain high transmittance after damp heat and UV aging per IEC-related test sequences.
- Architectural glass and window films, where energy performance depends on stable light and solar transmittance values.
- Consumer electronics and wearables, including smartwatch cover lenses, camera windows, and protective coatings.
- Optical components and lighting products, such as lenses, diffusers, and light guides used in LED-based systems.
FAQ
What is an optical transmittance change test report?
It is a formal document that records the luminous transmittance of a material before and after a specified treatment, calculates the change value, and states whether the result complies with the defined acceptance criteria. The report is issued after testing in accredited third-party laboratories and can be used for supplier approval, customer submission, or certification purposes.
Which standards are most commonly applied?
Frequently referenced standards include ASTM D1003 and ISO 13468 for total luminous transmittance of transparent plastics, ASTM D1003 and ISO 14782 for haze, ISO 9050 for glazing transmittance, GB/T 2410 for the Chinese market, JIS K 7361-1 for Japan, and ISO 4892 or ASTM G155 for the light-exposure conditioning that precedes the transmittance remeasurement.
How is the transmittance change calculated?
The change is calculated as ΔT = (T2 − T1) / T1 × 100%, where T1 is the initial transmittance and T2 is the transmittance after treatment. Some specifications instead use the absolute difference (T2 − T1) expressed in percentage points, so the calculation method is always stated explicitly in the report.
What sample preparation is required?
Specimens are usually cut into flat pieces of an appropriate size for the spectrophotometer sample port, typically 50 mm × 50 mm. Surfaces must be clean, free of fingerprints, scratches, and dust, and multiple specimens are recommended so that measurement variability can be assessed. For films, a supporting frame or substrate may be used to keep the specimen flat.
What is a typical turnaround time?
Baseline and post-treatment transmittance measurements themselves can be completed within a few working days. However, when the report includes long-duration conditioning such as 500 or 1000 hours of damp heat or UV exposure, the total project time depends on the specified aging period, and the laboratory will confirm the schedule during project planning.