ISO 13468-1 Total light luminous transmittance test of plastic

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ISO 13468-1 Standard | Single-Beam Total Luminous Transmittance Test Machine for Transparent Plastics | UnitedTest

UnitedTest is a professional manufacturer developing fully ISO 13468-1 compliant single-beam optical testing instruments for transparent plastic factories, packaging labs and optical component inspection centers worldwide.

ISO 13468-1 Plastics – Determination of the total luminous transmittance of transparent materials – Part 1: Single-beam instrument sets standardized laboratory procedures to calculate total luminous transmittance (τₜ) across the visible light spectrum. This test method relies on a calibrated single-beam photometer equipped with designated CIE standard light sources and matched photodetectors to capture precise light transmission data.

The standard’s testing scope covers flat, nearly colourless transparent plastic films, rigid sheets and molded plastic components with a maximum thickness of 10 mm. It also supports testing faintly tinted transparent plastic substrates to quantify their overall visible light passage performance. Total luminous transmittance values measured per ISO 13468-1 act as core quality benchmarks for packaging, optical plastic and injection molding product quality control and material R&D validation.

Our UnitedTest single-beam transmittance tester adheres strictly to all CIE light source calibration, specimen thickness limits, photometer setup and data calculation rules outlined in ISO 13468-1, delivering stable, repeatable luminous transmittance measurement results for global polymer manufacturers and third-party compliance testing labs.

Core Test Principle

Total luminous transmittance describes the percentage of human-eye-weighted visible luminous flux passing through a plastic sample, including both straight collimated light and wide-angle scattered light.

Optical compensation logic (Annex A mathematical basis):

The integrating sphere’s light collection efficiency fluctuates when ports are covered/uncovered. The dual-port (entrance + compensation) design cancels this error by taking two symmetric flux readings:

τ₁ measures baseline flux with the specimen covering the compensation port to account for sphere reflectance loss.

τ₂ measures total transmitted flux with the specimen covering the entrance port.

Shared efficiency variables in the two readings cancel out in the division formula, eliminating systematic instrument bias without external calibration standards.

Measurement physical logic: Mounting the specimen directly against the sphere entrance port captures all hemispherical transmitted light (direct + diffuse), which is the definition of total luminous transmittance (distinct from regular collimated transmittance measured with specimens spaced away from the sphere).

Test Methods

ISO 13468-1 defines one unified single-beam integrating sphere compensation method with only two primary light flux measurements required for calculation.

Core design feature: Built-in compensation port eliminates measurement errors caused by integrating sphere efficiency loss from covered ports, removing mandatory calibration with reference plaques for routine testing (mathematical compensation cancels sphere efficiency variables)ISO.

Two-measurement workflow:

τ₁: Baseline full incident luminous flux (specimen covers compensation port, light trap on entrance port; instrument set to read τ₁ = 100%)

τ₂: Total transmitted flux (specimen covers entrance port, light trap on compensation port)

Calculation formula for total luminous transmittance (τₜ, %):

τₜ = (τ₂ / τ₁) × 100

Method positioning: Designed for factory daily QC screening; paired with ISO 14782:2021 haze testing to fully characterize plastic optical clarity.

Test Specimen Requirements

Source	Cut from film, sheet, or injection/compression‑moulded articles
Surface	Free of defects, dust, grease, protective‑film adhesive, scratches, blemishes, visible internal voids/particle
Size	Large enough to cover entrance + compensation ports. For 150 mm sphere → ⌀ 50 mm or 60 mm disc (or square of same side) recommended
Quantity	3 specimens per sample unless otherwise specified
Thickness measured	3 points: ±0.02 mm (sheet), ±1 µm (film)

Test Equipment Required for ISO 13468-1 Total light luminous transmittance test of plastic

Single-Beam Photometer with Integrating Sphere	UnitedTest Transmission and Haze testing machine can easily realize ASTM D1003 non compensating method, ISO 13468, ISO 14782 compensating method, full transmittance and haze testing. The open sample chamber can be tested vertically or horizontally to adapt to more tested samples. Any sphere diameter allowed; recommended minimum 150 mm for standard 50/60 mm specimens. Total port area ≤3.0% of sphere internal reflective surface area. Entrance and compensation ports are identical circular size; entrance, compensation and detector ports cannot share the same great circle of the sphere. Inner sphere walls and baffles: Y₁₀ tristimulus reflectance ≥90%, variation ≤±3%.
Light source & photodetector optical filters	Matches CIE D65 standard illuminant and CIE standard colorimetric observer (ISO 11664-1/-2). Photodetector linearity error ≤1% across full working flux range; light source output must remain stable during all specimen tests. Optical design prevents specimen temperature rise during measurement.
Collimated parallel beam system	Maximum ray divergence angle relative to beam axis ≤0.087 rad (5°). Beam diameter = 0.5 ~ 0.8 × entrance port diameter; no vignetting at sphere ports.
Photodetector assembly	Equipped with light baffles to block direct light from specimen hitting the detector.
Light traps	Minimum 95% light absorption efficiency for blocking collimated beam during baseline calibration.
Specimen holder	Fixes specimen perpendicular to light beam within ±2° tolerance, mounted tightly against sphere entrance port to capture all scattered transmitted light. Flexible thin films: double-ring edge clamp or double-sided adhesive tape to eliminate wrinkling; vacuum plate is also an acceptable mounting solution.

Mandatory Test Parameters and stipulation:

Instrument performance fixed parameters

Repeatability standard deviation ≤0.2% transmittance within the same lab.

Long-term within-laboratory reproducibility shall not exceed repeatability by a factor of 3.

Light trap absorption efficiency ≥95%.

Sphere inner wall reflectance ≥90% Y₁₀ value, variation limited to ±3%.

Geometric optical constants

Collimated beam maximum divergence: 0.087 rad (5°)

Total sphere port area cap: 3.0% of internal reflective surface

Specimen perpendicularity tolerance relative to beam: ±2°

Standard Test Procedures ISO 13468-1 Total light luminous transmittance test of plastic:

Specimen preparation and cleaning

Cut samples to standard 50/60 mm size, wipe all surface contaminants, inspect for internal flaws; prepare three replicate specimens. Measure thickness at three points per specimen and calculate average thickness.

Specimen conditioning

Place all replicates in ISO 291 climate chamber for the required duration (16 h for ultra-thin films, ≥40 h for thick sheets) at 23±2 °C / 50±5% RH.

Instrument warm-up

Power on the single-beam hazemeter/photometer and wait for full thermal equilibrium of light source, detector and integrating sphere.

Baseline measurement τ₁

Mount specimen over the compensation port, install light trap on the entrance port; adjust the instrument to set τ₁ reading equal to 100%.

Transmittance measurement τ₂

Move the specimen to cover the entrance port, place light trap on the compensation port; record τ₂ flux value.

Uniformity validation

Reposition the specimen to multiple positions and repeat τ₁/τ₂ readings to check optical consistency across the sample surface.

Repeat full measurement sequence for all three replicate specimens.

Result calculation

Compute total luminous transmittance τₜ for each replicate using the standard formula, average the three values and round to the nearest 0.1% as the final test result.

Industry Application Fields

ISO 13468-1 is the primary international single-beam transmittance test standard for global plastic manufacturing, widely adopted across EU, Asia, Oceania and most export supply chains, covering these core sectors:

Flexible & rigid packaging: PET food films, transparent cosmetic containers, pharmaceutical sterile blister packs, transparent food storage mouldings

Automotive plastics: Headlight lenses, interior transparent instrument panels, automotive window films, sunroof glazing

Optoelectronics & consumer displays: Touch screen protective films, display cover substrates, LED transparent light diffuser sheets, optical filter plastic substrates

Construction & architectural plastics: Polycarbonate window glazing, transparent PVC roof panels, anti-UV clear building sheets

Medical transparent plastics: IV fluid containers, transparent surgical device housings

Related Standard:

ASTM D1003	Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
GB/T 2410	Determination of light transmittance and haze of transparent plastics
UNI 8028	Transparent plastics sheets and films. Determination of the total luminous transmittance and haze.
ASTM D1044	Abrasion resistance test for transparent plastics (narrow-angle scattering measurement for scratched samples)
ASTM E2387	Goniometric Optical Scatter Measurements (for high-haze >30% diffusing plastics)
ISO 13468-1	Plastics – Total luminous transmittance of transparent materials
ISO 14782	Plastics – Haze measurement of transparent materials
JIS K 7136	Plastics -- Determination of haze for transparent materials

Keywords: UnitedTest ISO 13468-1 tester, ISO 13468-1 single-beam total luminous transmittance machine, transparent plastic visible light transmittance testing equipment, single-beam photometer plastic optical tester, total luminous transmittance τₜ measurement for planar plastic, CIE standard light source single-beam transmittance analyzer, ≤10mm thick transparent plastic film sheet molded part test, faintly tinted plastic light transmission inspection instrument

Transmission and Haze testing machine (General type) can easily realize ASTM D1003 non compensating method, ISO 13468 compensating method, full transmittance and haze testing. The open sample chamber can be tested vertically or horizontally to adapt to more tested samples.

Q1: What optical property does ISO 13468-1 measure, and what is its core testing principle?

A1: It measures total luminous transmittance (τₜ), the percentage of human-eye-weighted visible light that passes through flat transparent plastics, including both straight direct light and wide-angle scattered light. It uses a single-beam integrating sphere with a compensation port to eliminate sphere efficiency errors via two flux readings for simple, fast calculation: τₜ = (τ₂/τ₁) × 100.

Q2: What materials are excluded from ISO 13468-1 testing?

A2: Two main exclusions:

Plastics containing fluorescent additives (fluorescence distorts light flux readings and generates false high transmittance values).

Specimens thicker than 10 mm can be measured instrumentally, but their results cannot be compared with data from specimens ≤10 mm for compliance or specification acceptance.

Q3: What is the difference between ISO 13468-1 and ISO 13468-2?

A3: ISO 13468-1: Single-beam instrument, only two measurements, fast, low-cost, designed for daily factory quality control.

ISO 13468-2: Double-beam spectrophotometer, full spectral data, higher precision for R&D, lab research and complex material analysis, slower operation.

For routine production QC, ISO 13468-1 is the preferred method.

Q4: Can ISO 13468-1 replace ISO 14782 for haze testing?

A4: No. ISO 13468-1 only measures total luminous transmittance (overall light throughput). ISO 14782:2021 is a separate standard dedicated to haze (wide-angle light scattering that causes blurriness). They are complementary and must both be tested to fully evaluate plastic optical clarity.

Q5: What is the key function of the compensation port required by ISO 13468-1’s integrating sphere?

A5: The integrating sphere’s light collection efficiency changes when ports are covered or uncovered, which creates systematic measurement bias. The compensation port cancels this error mathematically by taking symmetric readings (specimen on compensation port for baseline τ₁; specimen on entrance port for transmitted τ₂). Shared efficiency variables cancel out in the formula, removing the need for frequent calibration with reference standards.

Q6. How precise is the method?

A6:

Material	τₜ	s_Rw	s_R
PMMA 2 mm	92.6 %	0.05	0.11
PMMA‑I 2 mm	92.3 %	0.06	0.13
PVC 2 mm	87.0 %	0.04	0.17
PS 2 mm	89.6 %	0.06	0.15
MABS 2 mm	89.8 %	0.05	0.10
PC 3 mm	88.3 %	0.04	0.23
PP film 50 µm	92.4 %	0.06	0.23
PP(SiO₂) 50 µm	92.1 %	0.04	0.24
PE‑HD 30 µm	90.7 %	0.04	0.23
PVDC 10 µm	90.3 %	0.08	0.22

Q7: How to mount thin flexible plastic films to avoid inaccurate transmittance readings?

A7: ISO 13468-1 permits three valid mounting methods: double-ring edge clamp, double-sided adhesive tape around specimen edges, or vacuum plate. The specimen must sit flat and perpendicular to the light beam within ±2° tolerance, tightly against the sphere entrance port to capture all scattered transmitted light.

Q8: What two core measurements (τ₁ and τ₂) do I need to collect, and how to set them up?

A8:

τ₁ (baseline flux): Specimen covers compensation port, light trap on entrance port; adjust instrument to set τ₁ = 100%.

τ₂ (total transmitted flux): Specimen covers entrance port, light trap on compensation port; record the reading.

Divide τ₂ by τ₁ and multiply by 100 to get percentage total luminous transmittance.

Q9: Why must the instrument warm up to thermal equilibrium before measuring?

A9: Light source brightness and photodetector sensitivity drift with temperature changes, which distorts τ₁ and τ₂ flux values and creates inconsistent transmittance results. Full thermal stabilization eliminates drift errors.

Q10: Is ISO 13468-1 equivalent to ASTM D1003-21? Can results be interchanged?

A10: No, they are not equivalent and results cannot be swapped for certification or customer acceptance. Key differences:

ISO 13468-1 uses a compensation port for error correction; ASTM D1003 has no compensation port design.

ASTM D1003 combines transmittance and haze into one standard; ISO separates transmittance (13468) and haze (14782).

Different sphere geometric tolerances, calculation formulas and upper thickness/haze limits.

North American projects typically require ASTM D1003 data; EU and global export chains follow ISO 13468-1 + ISO 14782.

Q11: Why is ISO 13468-1 testing essential for transparent plastic manufacturers?

A11: Global trade compliance: It is the primary international single-beam transmittance standard accepted across Europe, Asia and most export markets, required for nearly all cross-border plastic procurement contracts.

Efficient mass production QC: The two-step measurement process delivers rapid results, ideal for inline or daily batch screening compared to slower double-beam spectrophotometer testing (ISO 13468-2).

Quantify light throughput performance: Total luminous transmittance directly determines how much visible light passes through plastic. High transmittance is critical for automotive glazing, medical viewing parts and display covers; low transmittance reduces visibility and product functionality.

R&D formulation and process troubleshooting: Transmittance drop indicates root causes like resin impurities, additive agglomeration, uneven extrusion, coating defects or surface scratches, supporting optimization of polymer recipes and manufacturing processes.

Aging and durability validation: Measures transmittance loss after UV exposure, thermal cycling, chemical cleaning or abrasion to assess long-term weather resistance and product service life.

Contract acceptance evidence: Most international plastic material specifications reference ISO 13468-1 as the mandatory transmittance test method; standardized test reports act as objective pass/fail proof between suppliers and buyers.

Consistent cross-lab benchmarking: The compensation port design minimizes instrument-to-instrument systematic bias, ensuring uniform transmittance grading across multiple factories and third-party test laboratories.

Safety compliance verification: For safety-critical transparent plastics (automotive windows, medical devices, safety shields), stable high transmittance guarantees unobstructed vision and eliminates light-blocking hazards.

Q12: Which industries commonly implement ISO 13468-1 testing?

A12: Packaging: PET food films, cosmetic transparent containers, pharmaceutical sterile blister packs

Automotive: Headlight lenses, transparent interior panels, sunroof glazing, automotive window films

Optoelectronics: Touch screen protective films, display cover substrates, LED light diffuser sheets

Construction: Polycarbonate window sheets, transparent PVC architectural panels

Medical plastics: IV fluid containers, transparent medical device housings

Consumer goods: Eyeglass blanks, plastic tableware, appliance transparent panels

Coatings & surface finishing: Clear hard coat performance evaluation, post-aging light transmission loss testing

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