Product Light Transmittance Testing: Standards, Methods, and Applications

Product light transmittance testing measures the percentage of visible light that passes through transparent and translucent materials, providing essential data for quality control, regulatory compliance, and product development. This technical guide explains the principles of transmittance and haze measurement, applicable international standards, sample requirements, and typical industry applications. Whether you manufacture optical plastics, packaging films, automotive glazing, or display covers, understanding light transmittance testing helps ensure your products meet precise optical performance specifications.

Technical Overview

Light transmittance testing is a quantitative optical measurement that determines how efficiently a material allows visible light to pass through it. Transmittance is expressed as the ratio of transmitted luminous flux to incident luminous flux, typically reported as a percentage. A perfectly transparent material would theoretically achieve 100 percent transmittance, while real-world materials scatter, absorb, and reflect a portion of the incoming light.

The measurement is typically performed using the photopic response of the human eye, defined by the CIE standard observer and CIE standard illuminant A or D65. In practice, a spectrophotometer or hazemeter equipped with an integrating sphere collects both directly transmitted light and diffusely scattered light, allowing the instrument to calculate total luminous transmittance, regular transmittance, and haze simultaneously.

Transmittance is closely related to haze, which quantifies the percentage of transmitted light that is scattered by more than 2.5 degrees from the incident beam direction. High transmittance combined with low haze indicates a clear, optically pure material, while high transmittance with high haze indicates a diffusing or milky material. Together, these two parameters define the optical quality of transparent products across nearly every manufacturing sector.

Testing Samples

Rigid Transparent Plastics

Thermoplastic sheets and molded parts are among the most frequently tested sample types. Common materials include polymethyl methacrylate (PMMA, acrylic), polycarbonate (PC), polystyrene (PS), polyethylene terephthalate (PET), styrene-acrylonitrile (SAN), and cyclic olefin copolymer (COC). These materials are widely used in lenses, light guides, appliance windows, and protective covers where optical clarity is a critical performance attribute.

Flexible Films and Sheets

Packaging films, optical films, agricultural films, and adhesive films can be tested either as single layers or as multilayer laminates. Because thin films may curl or wrinkle, samples are typically mounted flat in a specialized film holder to ensure reproducible measurement geometry.

Glass and Coated Glass

Architectural glass, automotive glazing, cover glass for electronics, and anti-reflective or conductive coated glass products are tested to verify compliance with building energy codes, automotive safety regulations, and display performance requirements. Coated samples must be measured with the coating orientation documented, since coatings are often directionally sensitive.

Optical Components and Lenses

Camera lenses, LED diffusers, light pipes, protective windows, and display panels may be tested for transmittance and haze. Curved or thick components require careful fixturing to ensure the light beam passes through the sample consistently, and thickness must always be reported alongside the result.

Liquids and Coatings on Substrates

Transparent liquids, varnishes, and coating layers can be evaluated by measuring transmittance through a standard quartz cuvette or by comparing coated substrates against uncoated references to isolate the contribution of the coating itself.

Testing Items

Light transmittance testing programs typically include the following measurable parameters:

• Total luminous transmittance (Tt): the overall percentage of incident visible light that passes through the sample, including both direct and scattered components.
• Regular (direct) transmittance: the percentage of light transmitted without deviation from the original beam path, calculated as total transmittance minus diffuse transmittance.
• Diffuse transmittance (Td): the percentage of transmitted light scattered by angles greater than 2.5 degrees from the incident direction.
• Haze: the ratio of diffuse transmittance to total transmittance, expressed as a percentage and used to quantify milkiness or cloudiness.
• Spectral transmittance curve: transmittance values measured across a defined wavelength range, such as 380 to 780 nanometers for visible light, or extended into ultraviolet (UV) and infrared (IR) regions.
• UV transmittance and IR transmittance: wavelength-specific blocking performance relevant for sunscreen packaging, eyewear, and energy-efficient glazing.
• Clarity: a parameter describing the ability of a material to resolve fine image detail, sometimes measured for high-precision optical applications.

Testing Methods

Testing is performed according to recognized international standards that define instrument geometry, illuminant conditions, and calculation procedures. The most commonly applied standards include:

• ASTM D1003: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, the dominant method in North America.
• ISO 13468-1 and ISO 13468-2: Determination of the total luminous transmittance of transparent materials, using single-beam and double-beam instrument configurations respectively.
• ISO 14782: Determination of haze for transparent materials, the international counterpart to the haze portion of ASTM D1003.
• GB/T 2410: Chinese national standard for the determination of light transmittance and haze of transparent plastics, widely referenced for products sold in the Chinese market.
• JIS K 7361 and JIS K 7136: Japanese industrial standards corresponding to total transmittance and haze measurement.

A typical test procedure begins with sample preparation, in which specimens are cut to the required size, cleaned with lint-free wipes and appropriate solvents, and conditioned in a controlled laboratory environment, usually at 23 degrees Celsius and 50 percent relative humidity. The instrument is then calibrated using a reference standard, and baseline readings are taken with the sample port empty or with a reference air path. The specimen is placed perpendicular to the light beam, and measurements of total transmittance, diffuse transmittance, and haze are recorded. Multiple readings at different positions on the sample are averaged to account for material non-uniformity.

Instrumentation is typically based on either a dedicated hazemeter or a UV-Vis spectrophotometer fitted with an integrating sphere attachment. Spectrophotometer-based methods provide full spectral data, while dedicated hazemeters offer fast, repeatable measurements well suited to production quality control. Measurement uncertainty generally falls within plus or minus 0.5 percent for transmittance and plus or minus 0.3 percent for haze on well-prepared samples, with results always reported together with sample thickness, color, surface condition, and the specific standard applied.

Applications

Light transmittance testing supports product development and compliance verification across a broad range of industries:

• Automotive: windshield and side glazing light transmittance verification, where regulations commonly require minimum visible transmittance values of 70 percent or higher for driver visibility zones.
• Packaging: ensuring transparent films and containers allow adequate product visibility while providing UV protection for light-sensitive foods, pharmaceuticals, and cosmetics.
• Electronics and displays: qualification of cover glass, touch panel substrates, polarizers, and diffusion films used in smartphones, monitors, and televisions.
• Construction and architecture: confirming that window glass, polycarbonate roofing, and skylight panels meet daylighting and energy-efficiency specifications.
• Lighting and LED: characterization of diffusers, lenses, and light guides to balance transmittance efficiency against glare control and uniformity.
• Medical and pharmaceutical: validation of transparent infusion components, blister packaging, and protective barriers where visual inspection of contents is required.
• Eyewear and safety equipment: certification of protective visors, goggles, and sunglass lenses against optical category and transmittance classifications.
• Agriculture: evaluation of greenhouse films to optimize photosynthetically active radiation transmission for crop growth.

FAQ

What is the difference between transmittance and haze?

Transmittance measures how much light passes through a material in total, while haze measures how much of that transmitted light is scattered away from the straight-through direction. A material can have high transmittance but poor clarity if haze is high, which is why both parameters are usually reported together.

What sample size and thickness are required for testing?

Most standards require a flat specimen large enough to cover the instrument aperture, commonly a disk or square of approximately 50 millimeters, though smaller apertures can accommodate small parts. There is no fixed thickness limit, but thickness must be reported with the result because transmittance decreases as thickness increases.

Does sample color affect the measurement?

Yes. Luminous transmittance is weighted to the photopic response of the human eye, so tinted or colored samples yield lower visible transmittance values than clear samples of the same material. For colored materials, a full spectral transmittance curve provides more complete characterization.

Can curved or textured samples be tested?

Curved lenses and textured surfaces can be measured, but results may be less reproducible due to beam deviation and surface scattering. Specialized fixturing and multiple position readings are used to improve reliability, and the geometry should be documented in the test report.

How should samples be prepared before testing?

Specimens should be clean, dry, free of fingerprints and scratches, and conditioned in a standard laboratory atmosphere before measurement. Both surfaces should be wiped with lint-free material, and any protective films that would not be present in the final application should be removed.

Which standard should be selected for a specific product?

The appropriate standard depends on the target market and product specification. ASTM D1003 is widely accepted in North America, ISO 13468 and ISO 14782 dominate in international trade, and GB/T 2410 is commonly required for the Chinese market. The standards are technically harmonized, so results are generally comparable when instrument geometry is consistent.