Plastic Light Transmittance Testing Specification: Standards, Methods and Quality Requirements

Plastic light transmittance testing is an essential quality control procedure for evaluating the optical performance of transparent and translucent polymeric materials. This specification defines the sample requirements, testing items, instrumental methods, and acceptance criteria in accordance with internationally recognized standards such as ASTM D1003, ISO 13468-1, and GB/T 2410. Understanding these testing specifications enables manufacturers to verify material consistency, meet regulatory requirements, and ensure end-product optical quality across packaging, automotive, optical, and construction applications.

Technical Overview

Light transmittance is defined as the ratio of luminous flux passing through a plastic specimen to the luminous flux incident upon it, expressed as a percentage. It is one of the most critical optical properties for transparent plastics such as polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), styrene-acrylonitrile (SAN), cyclic olefin copolymer (COC), and polyethylene terephthalate (PET). This specification establishes a uniform procedure for measuring total luminous transmittance and haze, ensuring reproducible results between laboratories and production facilities.

The governing reference standards for this specification include:

• ASTM D1003 – Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
• ISO 13468-1 – Plastics: Determination of the total luminous transmittance of transparent materials, Part 1: Single-beam instrument
• ISO 13468-2 – Plastics: Determination of the total luminous transmittance of transparent materials, Part 2: Double-beam instrument
• ISO 14782 – Plastics: Determination of haze for transparent materials
• GB/T 2410 – Determination of light transmittance and haze of transparent plastics
• JIS K 7361-1 and JIS K 7136 – Japanese national standards aligned with the corresponding ISO methods

Unless otherwise specified in the material data sheet or customer drawing, all tests shall be performed in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 10 % relative humidity, with specimens conditioned for a minimum of 40 hours prior to measurement.

Testing Samples

Specimen Geometry and Dimensions

Specimens shall be flat, parallel-surfaced plaques or sections free from sinks, flow lines, bubbles, scratches, and other visible defects that could bias the optical reading. The recommended specimen size is 50 mm × 50 mm (2 in × 2 in), or a disk of 50 mm diameter, sized to fully cover the instrument aperture. Test specimens representing films may be 60 mm × 60 mm to allow proper mounting in film holders.

Thickness Requirements

Because transmittance decreases with optical path length, the nominal thickness of the specimen must be recorded and reported with every result. Unless otherwise agreed, the reference thickness for molded plaques is 3.0 mm (1/8 in) for rigid plastics and 0.1 mm for thin films. When the finished part thickness differs from the reference thickness, measurements shall be taken on specimens of the actual part thickness and clearly identified as such.

Sample Preparation and Conditioning

• Molded plaques shall be produced under the recommended processing conditions for the resin, with mold temperature, melt temperature, and cycle time documented.
• All specimen surfaces shall be cleaned with lint-free wipes and, where appropriate, isopropyl alcohol or deionized water, then dried completely before testing.
• Protective films shall be removed no earlier than one hour before measurement to minimize surface contamination and electrostatic dust attraction.
• Antistatic treatment is permitted only where it does not alter the surface optical properties; the treatment shall be noted in the report.
• A minimum of three specimens per material lot shall be tested, and the arithmetic mean shall be reported together with individual values.

Testing Items

This specification covers the following optical performance characteristics of transparent plastic materials:

• Total Luminous Transmittance (Tt) – The percentage of incident luminous flux (photopic response of the human eye, CIE V(λ)) transmitted through the specimen, including both regular and diffuse components.
• Haze (Turbidity) – The percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam, caused by surface texture, internal inclusions, or crystallinity.
• Regular (Specular) Transmittance – The undeviated component of transmitted light, calculated as the difference between total transmittance and diffuse transmittance, relevant for glazing and lens applications.
• Diffuse Transmittance – The scattered component of transmitted light, relevant for lighting diffusers and backlighting panels.

Typical acceptance benchmarks, to be confirmed against the specific material grade and application, are provided below for guidance:

• PMMA optical grade: total transmittance ≥ 92 %, haze ≤ 1.0 % at 3 mm
• PC optical grade: total transmittance ≥ 88–90 %, haze ≤ 1.5 % at 3 mm
• General-purpose PS: total transmittance ≥ 88 %, haze ≤ 3.0 % at 3 mm
• PET packaging film: total transmittance ≥ 90 %, haze ≤ 2.0 % at 0.1 mm
• Lighting diffuser PC/PMMA: haze typically ≥ 70 % with total transmittance ≥ 75 %, as specified by the design requirement

Testing Methods

Method A – Hazemeter (Broad-Band Source)

Method A uses a hazemeter, which is a spectrally corrected, single-beam instrument equipped with an integrating sphere, a light source filtered to approximate CIE Standard Illuminant A, and a detector matched to the CIE 1931 standard colorimetric observer (2-degree field). This method, specified in ASTM D1003 Method A and GB/T 2410 Method A, measures total transmittance and haze simultaneously with high repeatability and is the preferred method for routine quality control.

The measurement sequence shall be executed as follows:

• Set the instrument to zero with the light trap in position and verify calibration using reference standards traceable to a national metrology institute.
• Measure the incident luminous flux T1 with no specimen and the sphere wall in the reference position.
• Place the specimen at the entry port and measure total transmitted flux T2.
• With the light trap in position, measure the instrument and surface scattered flux T3 (without specimen) and T4 (with specimen).
• Calculate total transmittance as Tt = 100 × T2 / T1 and haze as Haze = 100 × [(T3 / T1) − (T4 / T2)].

Method B – Spectrophotometer with Integrating Sphere

Method B employs a double-beam UV-Visible spectrophotometer fitted with an integrating sphere accessory. Transmittance is scanned across the visible spectrum, typically from 380 nm to 780 nm, and the total luminous transmittance is computed by weighting the spectral data with the chosen illuminant and observer functions, commonly CIE Standard Illuminant D65 with the CIE 1964 (10-degree) observer. This method, described in ASTM D1003 Method B, ISO 13468-2, and GB/T 2410 Method B, offers spectral information useful for material development and color analysis.

Instrument Calibration and Verification

• The instrument shall be calibrated at least daily, or before each measurement session, using certified transmittance and haze reference standards.
• Calibration records shall be maintained, and reference standards shall be re-certified at intervals not exceeding 12 months by an accredited calibration laboratory.
• Repeatability verification shall be performed by measuring a stable reference specimen five times; the range of readings shall not exceed 0.5 % for transmittance and 0.3 % for haze.
• The measurement port geometry and sphere condition shall be inspected regularly, as sphere wall contamination directly affects accuracy.

Report Content

Each test report shall include the following information: material identification and grade, specimen preparation method, nominal thickness and thickness tolerance, conditioning environment, test standard and method used (A or B), illuminant and observer, individual and mean transmittance values, individual and mean haze values, instrument model, and the date of testing and operator identification.

Applications

Light transmittance testing in accordance with this specification supports quality assurance and material qualification across a broad range of industries:

• Rigid and Flexible Packaging – Verification of clarity in PET bottles, thermoformed clamshells, and flexible films where shelf appeal and product visibility are essential.
• Automotive – Qualification of PC and PMMA glazing, headlamp lenses, light guides, and instrument panel covers against OEM optical specifications.
• Optics and Display – Incoming inspection of optical-grade resins used in lenses, prisms, touchscreen covers, and backlight modules.
• Lighting – Characterization of LED diffusers, lamp covers, and light pipes where a defined balance of transmittance and haze controls illumination uniformity.
• Construction and Glazing – Evaluation of transparent roofing sheets, safety glazing, and greenhouse films for daylighting performance and energy efficiency.
• Medical and Laboratory Ware – Confirmation of optical clarity for diagnostic consumables, cuvettes, and transparent enclosures where visual inspection of contents is required.

Where certification for regulatory submission is required, testing may be performed by accredited third-party laboratories operating under ISO/IEC 17025 management systems, using the methods defined in this specification.

FAQ

What is the difference between transmittance and haze? Transmittance quantifies how much visible light passes through the specimen as a percentage of the incident light, while haze quantifies how much of that transmitted light is scattered away from the direct beam. A material can exhibit high transmittance yet high haze, as in lighting diffusers, or high transmittance with very low haze, as in optical lenses.

Why does specimen thickness matter so much? Transmittance losses from absorption and bulk scattering accumulate along the optical path, so a thicker specimen of the same resin will generally show lower transmittance and higher haze. Comparisons between materials are only valid at equal, documented thicknesses.

Which standard should be selected: ASTM D1003 or ISO 13468? Both methods are technically equivalent in principle but differ in default illuminant and observer geometry. The choice is typically dictated by the customer specification, the target market (North American specifications commonly cite ASTM, while European and Asian specifications commonly cite ISO or the equivalent national standards), or contractual requirements.

What causes out-of-specification haze in production? Common root causes include excessive moisture in the resin leading to hydrolysis or silver streaks, contaminated regrind, high melt temperatures causing degradation, excessive mold release agent, poor polishing or texture on tool surfaces, and embedded particulates from inadequate filtration of the melt.

How often should transmittance testing be performed? For incoming material inspection, each resin lot should be verified against the specification limits. For production control, testing frequency is defined by the control plan, typically per shift or per production batch, with tightened sampling whenever a process change occurs.