A plastic light transmittance test report documents the measured ability of transparent and translucent plastic materials to transmit visible light, providing critical data for material qualification in automotive, packaging, electronics, and construction industries. This article explains the key optical parameters, internationally recognized test standards such as ASTM D1003 and ISO 13468, sample preparation requirements, typical test results for common plastics, and how to correctly interpret an accredited third-party laboratory report.
Technical Overview
Light transmittance, also known as luminous transmittance, is defined as the ratio of luminous flux transmitted through a plastic specimen to the luminous flux incident upon it, expressed as a percentage. It is one of the most important optical performance indicators for transparent and translucent polymeric materials, directly determining whether a material is suitable for applications such as glazing, display windows, lighting diffusers, and transparent packaging.
A complete plastic light transmittance test report typically contains two related optical parameters: total luminous transmittance (Tt) and haze (H). While transmittance quantifies how much light passes through the specimen, haze measures the percentage of transmitted light that deviates from the incident beam direction by more than 2.5 degrees due to scattering. A material can exhibit high transmittance yet high haze, such as an opal lighting diffuser, or high transmittance with extremely low haze, such as optical-grade PMMA. Both parameters must therefore be evaluated together to fully characterize optical quality.
The measurement is performed using a hazemeter or a spectrophotometer equipped with an integrating sphere, operated under the illuminant A condition and the photopic response of the human eye (CIE 1931 standard observer). Specimens must be flat, free from scratches, fingerprints, and embedded bubbles, because surface defects and internal inclusions scatter light and distort the measured values.
Testing Samples
Light transmittance testing is applicable to a wide range of transparent and translucent plastic materials in sheet, film, or molded plaque form. Specimens are normally cut to a size compatible with the instrument aperture, typically 50 mm × 50 mm squares or 50 mm diameter discs, and conditioned to equilibrium before measurement.
Amorphous Transparent Plastics
Amorphous polymers are inherently transparent because their disordered molecular structure does not scatter visible light significantly. Common examples include polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and amorphous polyethylene terephthalate (APET). These materials achieve total transmittance values in the range of 88–93% for nominal 3 mm thickness, making them the preferred choice for optical lenses, sight glasses, and display covers.
Crystalline and Semi-Crystalline Plastics
Semi-crystalline polymers such as polypropylene (PP), polyethylene (PE), polyamide (PA), and crystalline PET contain spherulitic structures that scatter light at phase boundaries. Their transmittance depends strongly on crystallinity, orientation, and nucleation; highly clarified polypropylene grades can reach 85–90% transmittance with low haze, whereas natural unmodified polyethylene films often show lower clarity and higher haze values.
Transparent Films and Sheets
Thin flexible films made of PET, PVC, PE, PP, PLA, or cellulose acetate are widely tested for packaging and agricultural applications. Because transmittance is thickness-dependent, film specimens must be tested at their actual use thickness, and the report must state the measured thickness of each specimen.
Colored and Functional Glazing Materials
Tinted polycarbonate or acrylic glazing, IR-absorbing films, and anti-glare sheets are tested to verify that transmittance remains within specified limits while achieving the desired solar control or aesthetic function.
Testing Items
A standard plastic light transmittance test report includes the following measurable items:
- Total luminous transmittance (Tt): the percentage of incident visible light that passes through the specimen, including both regular and diffuse components.
- Regular transmittance (Tr): the percentage of light transmitted without deviation from the incident direction, calculated as Tt minus the diffuse transmittance.
- Diffuse transmittance (Td): the scattered portion of transmitted light, used for haze calculation.
- Haze (H): the percentage of transmitted light scattered more than 2.5 degrees from the incident beam axis, calculated as Td/Tt × 100.
- Clarity: the ability of a specimen to resolve fine image detail, applicable where see-through quality is critical, measured per ASTM D1746 for planar sheeting.
- Transmittance wavelength dependence: full spectral transmittance curves from 380 nm to 780 nm when spectrophotometric methods such as ISO 13468-2 are used.
Testing Methods
Several internationally recognized standards govern the measurement of light transmittance and haze of plastics. The choice of method depends on the target market, product specification, and customer requirements. All measurements should be conducted in an environment of 23 ± 2 °C and 50 ± 10% relative humidity after adequate conditioning, following ISO 291 or ASTM D618.
ASTM D1003
ASTM D1003, Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, is the most widely referenced method in North America. Method A uses a hazemeter with a standardized integrating sphere and an uncollimated light beam, while Method B uses a spectrophotometer, allowing spectral data acquisition across the visible range. The standard is technically equivalent to ISO 14782 for haze and ISO 13468-1 for transmittance in most respects, and interlaboratory results are generally comparable.
ISO 13468-1 and ISO 13468-2
ISO 13468 specifies the determination of total luminous transmittance of transparent materials. Part 1 describes the single-beam instrument method using an integrating sphere, suitable for routine quality control. Part 2 describes the double-beam spectrophotometric method, which provides higher accuracy by simultaneously compensating for source drift and is suitable for certification testing and thin-film measurements.
ISO 14782
ISO 14782 defines the precise method for measuring haze of transparent plastics using a hazemeter with collimated illumination. It specifies the 2.5 degree collection criterion, sphere geometry, and calibration procedures, and it includes a rigorous correction formula for instrument-measured haze and luminous transmittance of the empty sphere.
GB/T 2410 and JIS Standards
GB/T 2410 is the Chinese national standard for the determination of light transmittance and haze of transparent plastics, technically aligned with ASTM D1003 and widely specified in Chinese domestic supply chains. For the Japanese market, JIS K 7361-1 covers total luminous transmittance and JIS K 7136 covers haze, both harmonized with the corresponding ISO methods. Cross-referencing these standards is acceptable in most specifications, but the report should always identify which standard was actually applied.
Instrumentation and Calibration
The test equipment consists of a stabilized light source, illuminant A filter, photometric detector matched to the CIE photopic response, and a 150 mm integrating sphere with light trap and reference port. Calibration is verified before each test session using certified reference standards traceable to national metrology institutes. At least three specimens per material are measured, and the arithmetic mean, individual values, and standard deviation are reported.
Applications
Light transmittance test reports support material qualification, incoming inspection, and regulatory compliance across many industries:
- Automotive: headlamp lenses, panoramic roof glazing, instrument covers, and side windows require verified transmittance for safety and regulatory conformity.
- Construction and architecture: transparent roofing sheets, polycarbonate greenhouse panels, and architectural glazing rely on transmittance data for daylighting design and energy simulation.
- Lighting: LED diffusers, lamp shades, and light guides require controlled transmittance and haze balance to achieve uniform illumination.
- Consumer electronics and displays: touch panel covers, screen protectors, and optical windows must meet narrow transmittance tolerances, often above 91% with haze below 1%.
- Packaging: transparent films, blister packs, and rigid containers use transmittance and haze values to demonstrate product visibility and shelf appeal.
- Medical devices: transparent IV components, diagnostic cuvettes, and sterile packaging must transmit light adequately for visual inspection and optical detection.
- Agriculture: greenhouse films are characterized by total and PAR transmittance to optimize crop growth conditions.
FAQ
What is a good light transmittance value for plastics?
For transparent engineering applications, PMMA and PS typically achieve 92–93%, optical-grade PC reaches 88–90%, and clarified PP reaches 85–90% at comparable thickness. Values above 90% with haze below 1–2% are generally considered optical grade. However, acceptance criteria are always application-specific and should be defined in the product specification.
Does specimen thickness affect the test result?
Yes. Transmittance decreases and haze increases with thickness due to bulk absorption and scattering. A single material can show 93% at 1 mm but only 89% at 5 mm. The test report must therefore state the nominal and measured specimen thickness, and comparisons between materials are only valid at equal thickness.
Can ASTM D1003 and ISO 13468 results be directly compared?
In most cases the results are numerically very close and technically acceptable for cross-reference, because the optical geometry is harmonized. Nevertheless, subtle differences in beam geometry, sphere calibration, and haze correction equations can introduce small deviations, so certification testing should follow the exact standard named in the purchase specification.
What information should a complete test report contain?
A professional report should include: laboratory identification and accreditation scope; client and sample identification; material designation and color; test standard and method; specimen dimensions, thickness, and quantity; conditioning environment; instrument model and calibration status; individual and mean transmittance and haze values; test date; and a clear statement of measurement uncertainty where applicable.
How many specimens are required for a reliable test?
Most standards recommend testing at least three specimens from different locations of the sample, with the average value reported. For certification or borderline results, five or more specimens provide better statistical confidence.
How should samples be prepared and shipped for testing?
Specimens should be flat, clean, and representative of production material. Protective films should be removed, and surfaces must be free of dust, grease, and abrasion. Samples should be shipped with interleaving protection to prevent scratching, accompanied by material specifications, target thickness, and the required test standard.