Polarizer Light Transmittance Testing: Standards, Methods and Key Optical Parameters

Polarizer light transmittance testing measures how efficiently polarizing optical films transmit light, a decisive quality parameter for LCD panels, OLED displays, and other photonic devices. This technical guide explains the core transmittance metrics—single, parallel, and crossed transmittance—along with polarization efficiency, haze, and chromaticity, and summarizes the internationally recognized standards and laboratory methods, such as ASTM D1003 and ISO 13468, used by accredited third-party laboratories to qualify polarizer products.

Technical Overview

A polarizer is a multilayer optical film that converts unpolarized light into linearly polarized light. In its most common construction, a stretched and iodine- or dye-stained polyvinyl alcohol (PVA) layer is laminated between triacetyl cellulose (TAC) or cycloolefin polymer (COP) substrates, and the composite is finished with adhesive, protective, and release films. Because the polarizer sits directly in the optical path of every liquid crystal display, its light transmittance directly determines panel brightness, power consumption, and contrast performance.

Light transmittance is defined as the ratio of transmitted luminous flux to incident luminous flux, evaluated over the visible spectrum (380–780 nm) using the CIE photopic response function and a standard D65 illuminant. For polarizers, transmittance cannot be described by a single number: it must be characterized in three distinct optical configurations—single-plate, parallel-pair, and crossed-pair—and interpreted together with polarization efficiency, haze, and chromaticity to fully describe film quality.

Transmittance testing is typically performed by accredited third-party laboratories or in-house optical characterization facilities using ultraviolet-visible (UV-Vis) spectrophotometers equipped with integrating spheres and polarization fixtures. Consistent, standards-based measurement is essential for comparing supplier lots, verifying conformance to purchase specifications, and supporting quality control in display manufacturing.

Testing Samples

Bare Polarizing Film

Unlaminated or base polarizing film is tested to evaluate the intrinsic optical performance of the PVA polarization layer. Specimens are cut to the required aperture size, surface contamination is removed with clean compressed air or lint-free wipes, and protective/release liners are peeled immediately before measurement to prevent contamination and moisture uptake.

Functional Composite Polarizers

Production-grade polarizers often integrate additional functional layers such as anti-glare (AG), anti-reflection (AR), wide-view compensation, and brightness enhancement films. These composites are tested in their delivered configuration because the functional coatings measurably alter total transmittance, haze, and color coordinates.

LCD Panels and Display Modules

Assembled cells and modules can be measured to verify the combined transmittance of the two internal polarizers together with the liquid crystal layer, supporting module-level brightness qualification and failure analysis.

Sample Preparation and Conditioning

• Specimen size: typically at least 50 mm × 50 mm, or sufficient to fully cover the instrument aperture; multiple specimens are recommended for uniformity assessment.
• Conditioning: 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 24 hours to stabilize the hygroscopic PVA layer.
• Handling: powder-free gloves, dust-free environment, and avoidance of fingerprints, scratches, bubbles, and wrinkles, all of which bias transmittance and haze readings.

Testing Items

A complete polarizer transmittance evaluation typically includes the following measurable parameters:

• Single-plate transmittance (Ts): transmittance of one polarizer measured with unpolarized incident light, typically 42–46% for commercial iodine-type films.
• Parallel transmittance (Tp): transmittance of two identical polarizers with their transmission axes aligned at 0°, typically 34–40%.
• Crossed transmittance (Tc): transmittance of two polarizers with transmission axes rotated 90° to each other; high-grade films achieve values below 0.05%, directly linked to display contrast.
• Polarization efficiency (PE): the degree to which the film converts light into a single polarization state, typically required to be ≥ 99.5% or ≥ 99.9%.
• Spectral transmittance curve: wavelength-dependent transmittance from 380 nm to 780 nm, used to detect absorption bands and color non-uniformity.
• Haze: wide-angle scattering ratio, generally specified below 1.0% (or 0.5% for optical-grade films).
• Chromaticity: CIE color coordinates (a*, b*) and yellowness index, evaluated with a D65 illuminant and a 2° or 10° standard observer.

Testing Methods

Instrumentation

Measurements are performed with a double-beam UV-Vis spectrophotometer fitted with an integrating sphere, preferably 150 mm in diameter to satisfy haze measurement geometry. Polarization test fixtures and precision rotating holders allow two specimens to be mounted with controlled relative angles of 0° and 90°. The system is verified with certified transmittance and haze reference standards before each test session.

Test Procedure

• Calibrate the instrument with a blank air reference and certified reference materials for total transmittance and haze.
• Remove release and protective films from the conditioned specimens and mount them cleanly at the sphere port.
• Measure single-plate transmittance Ts of each specimen with unpolarized illumination.
• Mount two specimens with transmission axes parallel (0°) to obtain Tp, then rotate one specimen by 90° to obtain Tc.
• Scan the spectral transmittance from 380 nm to 780 nm and compute photopic (D65-weighted) values automatically.
• Repeat measurements at multiple positions or on multiple specimens and report mean values together with the observed range.

Calculation of Polarization Efficiency

Polarization efficiency is derived from the paired measurements using the relationship PE (%) = 100 × [(Tp − Tc)/(Tp + Tc)]^0.5. Because Tc appears directly in the numerator, even small measurement errors in the crossed configuration significantly influence the result, which is why low-photometric-noise instrumentation and meticulous sample alignment are mandatory for reliable PE values.

Applicable Standards

• ASTM D1003: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics.
• ISO 13468-1 and ISO 13468-2: Plastics — Determination of the total luminous transmittance of transparent materials.
• ISO 14782: Plastics — Determination of haze for transparent materials.
• GB/T 2410: Chinese national standard for light transmittance and haze of transparent plastics.
• JIS K 7361-1 and JIS K 7136: Japanese industrial standards harmonized with the corresponding ISO methods for total luminous transmittance and haze.
• IEC 61747 series: relevant optical measurement framework context for liquid crystal display devices.

Applications

Polarizer transmittance testing supports quality assurance and product development across the display and optics industries:

• Incoming inspection of polarizer rolls and sheets by LCD panel manufacturers before lamination.
• Outgoing quality control and lot release by polarizer producers against customer optical specifications.
• Verification of circular polarizers used on OLED displays, where transmittance balance affects reflection suppression and luminance.
• Qualification of automotive and avionics displays, where high single-plate transmittance is required for sunlight readability and energy efficiency.
• Research and development of advanced films, including dye-type, wide-band, low-haze, and ultra-high-transmission polarizers.
• Reliability studies that track transmittance degradation after damp heat, thermal cycling, UV exposure, and accelerated aging.
• Failure analysis of brightness defects, contrast loss, and yellowing in returned panels and modules.
• Optical component verification for sunglasses, camera filters, and polarization-based instrumentation.

FAQ

What is the difference between single, parallel, and crossed transmittance?

Single transmittance describes one film measured alone with unpolarized light and reflects overall brightness potential. Parallel transmittance is obtained with two films whose axes are aligned, while crossed transmittance is measured with the axes perpendicular. The parallel value drives maximum panel luminance, whereas the crossed value—ideally close to zero—determines dark-state leakage and contrast.

What transmittance values are considered acceptable?

Typical commercial iodine polarizers exhibit single-plate transmittance of 42–46%, parallel transmittance of 34–40%, crossed transmittance below 0.1% (below 0.05% for premium grades), and polarization efficiency of at least 99.5%. Exact limits are always defined in the customer's purchase specification.

Why must samples be conditioned before testing?

The PVA polarization layer is hygroscopic, and its thickness and iodine complex state vary with ambient humidity and temperature. Conditioning at 23 ± 2 °C and 50 ± 5% relative humidity stabilizes the film so that measured transmittance reflects the material rather than transient environmental effects.

Which standards govern the measurement?

Total luminous transmittance is measured according to ASTM D1003, ISO 13468, GB/T 2410, or JIS K 7361-1; haze is measured according to ASTM D1003, ISO 14782, GB/T 2410, or JIS K 7136. Polarization-specific paired measurements follow the optical geometry described in the relevant liquid crystal display device standards of the IEC 61747 series and customer-defined procedures.

How large should test specimens be?

Specimens must fully cover the integrating sphere aperture, which in practice means samples of at least 50 mm × 50 mm for common bench instruments. Multiple specimens cut from different regions of a sheet or roll are measured to assess spatial uniformity, and results are reported as averages with a measured range.

Can transmittance be tested on finished display modules?

Yes. Module-level photometric testing measures the combined effect of the backlight, both polarizers, liquid crystal layer, and any compensation films. While it does not isolate the polarizer contribution, it is valuable for module brightness qualification and for diagnosing optical defects traced to polarizer degradation or lamination faults.