Light transmittance testing is an essential quality control procedure for transparent and translucent packaging materials, verifying that films, sheets, and rigid containers meet optical performance requirements before they reach production lines. This article explains the complete packaging material light transmittance testing process, covering applicable standards such as ASTM D1003, ISO 13468, ISO 14782, and GB/T 2410, along with sample preparation, measurement procedures, calculation methods, and reporting requirements. Understanding this workflow helps manufacturers in the food, pharmaceutical, and consumer goods sectors maintain batch-to-batch consistency and demonstrate compliance with customer specifications.
Technical Overview
Light transmittance, also known as total luminous transmittance (Tt), is defined as the ratio of luminous flux transmitted through a specimen to the luminous flux incident upon it, expressed as a percentage. For packaging materials, this parameter directly affects product visibility, shelf appeal, and, in applications such as pharmaceutical blister packs or greenhouse films, functional performance. The measurement is performed under standardized illumination—typically CIE Standard Illuminant A or D65—weighted against the photopic response of the human eye using the CIE 1931 standard observer function.
Closely related to transmittance is haze (turbidity), defined as the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam. Haze quantifies the loss of image contrast when viewing an object through the material, while transmittance quantifies the total amount of light passing through. Both parameters are usually measured together in a single test sequence using an integrating sphere instrument. Accredited third-party laboratories and in-house quality control departments typically conduct these tests in accordance with the following internationally recognized standards:
- ASTM D1003 — Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics (Method A: hazemeter; Method B: spectrophotometer)
- ISO 13468-1 / ISO 13468-2 — Plastics: Determination of the total luminous transmittance of transparent materials (Part 1: single-beam illuminant A; Part 2: illuminant D65)
- ISO 14782 — Plastics: Determination of haze for transparent materials
- GB/T 2410 — Chinese national standard for light transmittance and haze of transparent plastics, technically aligned with ASTM D1003
- JIS K 7361-1 and JIS K 7136 — Japanese industrial standards for total luminous transmittance and haze, respectively
Testing Samples
Flexible Films and Laminates
Single-layer and multilayer flexible films, such as BOPP, PET, PE, CPP, PVC, and metallized or coated laminates, represent the largest category of samples. Specimens must be flat, wrinkle-free, and free of creases, fingerprints, dust, or surface contamination, as any of these defects can artificially increase measured haze. Typical specimen size is at least 50 mm × 50 mm to fully cover the instrument transmittance port, although larger pieces are recommended so that multiple measurement positions can be evaluated.
Rigid Sheets and Thermoforming Films
Rigid and semi-rigid materials, including APET, RPET, PP, PS, PMMA, and PC sheets used for clamshells, trays, and transparent windows, are tested in the same manner. Because thickness strongly influences both transmittance and haze, the nominal thickness of each specimen must be recorded and reported. Specimens should be cut cleanly without edge chips or stress whitening, which can scatter light near the measurement area.
Pharmaceutical Blister and Lidding Materials
Blister base films such as PVC, PVDC-coated PVC, and cyclic olefin copolymers, as well as lidding foils with transparent windows, are tested to confirm tablet visibility and, where applicable, the UV-blocking performance of amber or opaque grades. For light-sensitive drug products, supplementary spectral transmittance scans in the UV region are frequently requested alongside the standard visible-range measurement.
Formed Containers and Converted Parts
Bottles, jars, and thermoformed components are not naturally flat, so test pieces are typically die-cut from flat, representative regions of the formed part or from companion flat plaques produced under identical processing conditions. This approach ensures geometric consistency while still reflecting the optical properties of the converted article.
Testing Items
A standard optical test report for packaging materials includes the following measured and calculated parameters:
- Total luminous transmittance (Tt) — the overall percentage of visible light passing through the specimen
- Diffuse transmittance (Td) — the percentage of light transmitted after scattering by the specimen
- Regular (specular) transmittance — the unscattered component, obtained as the difference between total and diffuse transmittance
- Haze — calculated as (Td / Tt) × 100%, representing wide-angle light scattering
- Spectral transmittance curve (optional) — full-wavelength data from approximately 380 nm to 780 nm, or extended into the UV range for light-protection verification
Testing Methods
Specimen Conditioning and Preparation
Prior to measurement, specimens are conditioned in a controlled atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity for a minimum of 40 hours in accordance with ISO 291 or ASTM D618. Conditioning stabilizes the polymer's optical state and removes moisture-related variability. At least three, and preferably five, replicate specimens from different positions across the web or sheet are prepared so that material uniformity can be assessed. Each specimen is inspected and, if necessary, cleaned with a lint-free wipe and suitable solvent that does not attack or stress-crack the polymer.
Instrument Calibration and Verification
The hazemeter or spectrophotometer is allowed to warm up according to the manufacturer's instructions, after which a full calibration sequence is performed: dark (zero) calibration with the beam blocked, and full-scale calibration against a certified reference standard traceable to a national metrology institute. Calibration is verified at intervals during the test session, and reference tiles are recalibrated on a scheduled basis to maintain traceability.
Method A: Hazemeter Measurement (ASTM D1003 Method A)
The classic four-reading sequence is performed using an integrating sphere photometer equipped with a light trap:
- T1 — incident light reading with no specimen installed and the light trap closed
- T2 — total light transmitted with the specimen installed and the light trap closed
- T3 — instrument-scattered light with no specimen installed and the light trap open
- T4 — total scattered light with the specimen installed and the light trap open
From these four readings, the key results are calculated as follows:
- Total transmittance: Tt = (T2 / T1) × 100 %
- Diffuse transmittance: Td = [(T4 − T3 × T2 / T1) / T1] × 100 %
- Haze = (Td / Tt) × 100 %
Method B: Spectrophotometer Measurement (ASTM D1003 Method B, ISO 13468)
In this approach, spectral transmittance is scanned across the visible range (typically 380–780 nm at 5 nm or finer intervals) using an integrating-sphere spectrophotometer. The spectral data are then mathematically weighted with the CIE photopic luminous efficiency function under the specified illuminant (A or D65) to yield total luminous transmittance. Method B provides additional diagnostic value because the full spectral curve reveals absorption bands from additives, colorants, or degradation products, and it can be extended into the UV region for light-barrier assessments.
Data Processing and Reporting
Measurements are taken at multiple positions on each specimen, and the mean, standard deviation, and range are calculated across all specimens. Under properly controlled conditions, within-laboratory repeatability is typically ±0.2 % for transmittance and ±0.3 % for haze on clear materials, while interlaboratory reproducibility is generally within ±1 %. The final test report, issued by an accredited third-party laboratory or internal quality department, should state: the applied standard and method, illuminant and observer geometry, specimen description and thickness, conditioning conditions, individual and mean results for Tt and haze, number of specimens and measurement positions, instrument model and calibration date, and any deviations from the standard.
Applications
Light transmittance and haze data support quality decisions across the entire packaging value chain:
- Food and beverage packaging — verifying the clarity of windows, flow wraps, and lidding films so that consumers can clearly see the product
- Pharmaceutical packaging — confirming tablet and capsule visibility through blister films and validating the UV-blocking performance of protective grades
- Agricultural and horticultural films — balancing total light transmission against controlled diffusion for greenhouse covering materials
- Cosmetic and personal care packaging — maintaining premium optical clarity of bottles, jars, and closures made from PET, PP, or PMMA
- Electronics and display packaging — evaluating protective films, anti-glare layers, and transparent windows
- Incoming inspection and supplier qualification — comparing optical data sheets against specification limits and monitoring batch consistency
- Research and development — quantifying the optical impact of resin selection, additive loading, orientation, crystallinity, and surface texturing
FAQ
What is the difference between light transmittance and haze?
Transmittance measures how much visible light passes through the material in total, while haze measures the fraction of that transmitted light that is scattered at wide angles, causing image blurring. Two films can have identical transmittance values but very different haze values, resulting in noticeably different see-through clarity.
Which standard should be specified: ASTM D1003 or ISO 13468?
Both methods produce comparable transmittance results when the same illuminant is used. ASTM D1003 is the dominant reference in North America, ISO 13468 and ISO 14782 are preferred in Europe and internationally, and GB/T 2410 is commonly required for the Chinese market. The choice is usually dictated by the end customer or the target regulatory region, and the standard used must be stated in the report.
What sample size and how many specimens are required?
Specimens must fully cover the instrument measurement port, typically requiring pieces of at least 50 mm × 50 mm. A minimum of three specimens per sample is recommended, with measurements at multiple positions on each, so that both measurement uncertainty and material uniformity can be evaluated.
Can translucent, colored, or printed materials be tested?
Yes. Translucent and tinted materials can be measured, though very high haze values and low transmittance values reduce measurement precision. Printed or heavily decorated areas should be avoided unless the test specifically targets those regions, and results for non-flat or textured surfaces should be interpreted with caution because surface geometry contributes to measured haze.
What are typical acceptance criteria for packaging films?
Requirements vary by application: high-clarity films for retail packaging often require transmittance above 90 % and haze below 3 %, whereas blister films may specify transmittance of 85–92 % with haze limits of 2–6 %. Acceptance limits are ultimately defined by the product specification between the brand owner and the material supplier.
How often should the instrument be calibrated and verified?
A full dark and standard calibration should be performed at the start of each test session, with verification checks after every ten to twenty specimens or whenever ambient conditions change significantly. Certified reference standards should be recalibrated on an annual cycle by an accredited metrology provider to preserve measurement traceability.