ISO 13468-2: Understanding Plastics’ Total Luminous Transmittance Measurement Using Dual-Beam Method

ISO 13468-2 is a specialized test method that measures how much light passes through plastic materials. This dual-beam approach helps manufacturers understand the optical properties of their plastic products, which is crucial for applications where clarity matters. The test provides valuable data about a material’s total luminous transmittance, which directly impacts product quality in industries like automotive, packaging, and electronics.

When plastic products need to be transparent or translucent, this test becomes essential. It works by comparing the intensity of light that passes through a plastic sample to a reference beam. You can use this method to evaluate various plastic materials including films, sheets, and molded parts. Unlike similar methods, ISO 13468-2’s dual-beam system compensates for light source fluctuations, making it more accurate.

Key Takeaways

• ISO 13468-2 measures how much light passes through plastic materials using a dual-beam system for greater accuracy.
• The test is vital for quality control in industries requiring transparent plastics like packaging, electronics, and automotive components.
• Proper implementation of this standard helps you ensure consistent optical properties and compare different plastic materials objectively.

Overview of ISO 13468‑2 and Its Significance

ISO 13468-2 provides a standardized method for determining total luminous transmittance of transparent plastics using a double-beam instrument. This test standard is essential for quality control and material specification in industries where optical clarity of plastics is critical.

Purpose of the Test Standard

ISO 13468-2 was developed to provide a reliable way to measure how much light passes through transparent plastic materials. The standard specifically focuses on the visible spectrum region, which matters most for optical applications.

This test helps manufacturers ensure their plastic products meet required transparency levels. When you need to verify if a plastic material will allow sufficient light transmission for applications like window glazing, protective screens, or optical components, this standard provides the answer.

The results from this test are expressed as a percentage of total luminous transmittance, giving you a clear quantitative value to compare against requirements or specifications.

Scope and Applicability

ISO 13468-2 applies to planar transparent plastics and is particularly useful for materials between 1mm and 10mm thick. The standard is designed for testing using double-beam instruments, which offer improved accuracy over single-beam methods.

You can use this test method for:

• Acrylic sheets
• Polycarbonate panels
• Transparent polymer films
• Other clear plastic materials

The test is valuable in industries such as:

• Automotive (for windows and light covers)
• Construction (for glazing materials)
• Electronics (for display screens)
• Packaging (for clear containers)

This standard helps you assess optical quality and ensure consistency across production batches.

Comparison with ISO 13468-1

ISO 13468-2 differs from ISO 13468-1 primarily in the instrumentation used. While ISO 13468-1 uses a single-beam instrument, ISO 13468-2 employs a double-beam instrument that provides several advantages.

The double-beam approach offers:

• Higher accuracy: By simultaneously measuring the reference and sample beams
• Better stability: Less affected by light source fluctuations
• Improved reliability: Reduces errors from environmental variations

You’ll find that double-beam measurements are less susceptible to drift over time. This makes ISO 13468-2 preferable when higher precision is required for quality control or research applications.

However, ISO 13468-1 might be sufficient for routine testing where ultimate precision isn’t critical, as single-beam equipment is typically less expensive and simpler to operate.

General Principles of Total Luminous Transmittance Measurement

The measurement of total luminous transmittance involves several key optical principles that help determine how much light passes through transparent plastic materials. These measurements are critical for quality control and product specifications in various industries.

Definition of Total Luminous Transmittance

Total luminous transmittance (τv) represents the ratio of transmitted luminous flux to incident luminous flux through a transparent material. Simply put, it measures how much visible light passes through a plastic sample.

This property is expressed as a percentage or decimal value between 0 and 1. A value of 100% indicates perfect transparency where all incident light passes through the material.

The measurement accounts for both direct transmission and diffuse transmission. Direct transmission occurs when light passes straight through without changing direction. Diffuse transmission happens when light scatters while passing through the material.

For plastic materials, this property helps determine optical clarity and is essential for applications requiring specific light transmission characteristics.

Fundamental Optical Concepts

When light interacts with transparent plastics, several phenomena occur simultaneously. Light can be transmitted, reflected, absorbed, or scattered by the material.

Transmission follows Snell’s Law, where light bends at the interface between different materials based on their refractive indices. This principle is fundamental to understanding how light travels through plastics.

Key optical factors affecting transmittance:

• Material thickness
• Surface roughness
• Internal structure
• Presence of additives or colorants
• Wavelength of incident light

The human eye perceives light differently across the visible spectrum (380-780 nm). ISO 13468 accounts for this by using CIE Standard Illuminant D65 and the photopic response of the human eye to weight measurements.

Role of Dual‑Beam Spectrophotometry

Dual-beam spectrophotometry provides advantages over single-beam methods described in ISO 13468-1. This technique uses two light paths: one passing through the sample and one reference path.

The dual-beam approach automatically compensates for fluctuations in light source intensity, detector sensitivity, and environmental conditions. This results in more accurate and reliable measurements.

The spectrophotometer splits light into wavelengths across the visible spectrum. It then compares the intensity of light through both paths to determine transmittance at each wavelength.

Benefits of dual-beam systems:

• Higher accuracy
• Better repeatability
• Reduced measurement time
• Automatic compensation for instrument drift

These systems are particularly valuable for quality control applications where precise measurements are required for product certification and specification compliance.

Specific Use and Intended Purpose

ISO 13468-2 provides a standardized method for measuring how much light passes through transparent plastic materials. This test helps manufacturers ensure quality control and select appropriate materials for specific applications where light transmission is important.

Evaluation Objectives

ISO 13468-2 measures the total luminous transmittance of transparent plastics using a double-beam spectrophotometer. This test determines what percentage of visible light passes through a plastic sample.

Unlike single-beam methods (ISO 13468-1), the double-beam approach offers higher accuracy by comparing the test sample against a reference simultaneously.

The standard works best with colorless or faintly tinted plastics up to 10mm thick. Thicker samples can be tested if the instrument allows, but results may not be comparable to standard measurements.

The test specifically excludes plastics containing fluorescent materials, as these would affect measurement accuracy.

Industry Applications

This standard is vital in industries requiring transparent materials with specific light transmission properties. Automotive manufacturers use it to test windshields and light covers for proper visibility and safety compliance.

Electronics producers rely on it for display screens and protective covers. The packaging industry needs it to verify that clear containers meet appearance and protection requirements.

Medical device makers use this test to ensure proper light transmission through diagnostic equipment, protective shields, and containers.

Construction companies apply this standard when selecting transparent materials for windows, skylights, and light fixtures. The test helps verify materials will provide expected natural lighting levels.

Benefits in Material Selection

Using ISO 13468-2 helps you make better decisions when choosing transparent plastics. You can objectively compare different materials based on their light transmission properties rather than visual inspection alone.

The test identifies subtle differences between similar-looking materials that might perform differently in your application. This prevents costly mistakes in material selection.

When developing new products, you can use test results to balance light transmission with other properties like impact resistance or UV protection.

The standard also helps you verify supplier claims about material properties. You can confirm that the materials you receive consistently meet your specifications for light transmission.

Materials and Products Covered by ISO 13468‑2

ISO 13468-2 specifically addresses transparent and substantially colorless plastic materials for which total luminous transmittance measurements are required. This standard provides a reliable method for evaluating light transmission properties using a double-beam scanning spectrophotometer.

Applicable Types of Plastic Sheets and Films

ISO 13468-2 applies to planar transparent plastics that allow light to pass through with minimal distortion. This includes acrylic sheets (PMMA), polycarbonate panels, polyethylene terephthalate (PET) films, and other clear thermoplastics.

The standard is particularly useful for testing optical-grade polymers used in displays, windows, and covers. Materials like clear polystyrene, transparent polyvinyl chloride (PVC), and polypropylene films commonly undergo this testing.

You can apply this standard to both rigid plastic sheets and flexible films, as long as they maintain planar geometry during measurement.

Sample Characteristics

Samples tested under ISO 13468-2 must be transparent or substantially colorless. The material should have minimal internal scattering to provide accurate transmittance values.

The standard works best with materials that have:

• Uniform thickness throughout the test area
• Planar surfaces without significant warping
• Limited surface defects that might scatter light
• No fluorescent additives (materials containing fluorescent compounds cannot be tested)

Sample preparation typically requires clean, dust-free specimens with minimal surface scratches or imperfections. Your samples should be properly conditioned according to relevant standards before testing.

Industries Utilizing This Standard

The automotive industry relies on ISO 13468-2 when developing and testing transparent plastics for headlamp covers, windows, and displays. Light transmission properties directly impact safety and functionality.

Building and construction sectors use this standard to evaluate glazing materials, skylights, and transparent building elements. The optical clarity and light transmission are critical for energy efficiency.

Electronics manufacturers apply these tests to screen protectors, display covers, and optical components. You’ll find this standard referenced in specifications for:

• Consumer electronics
• Medical device displays
• Optical instruments
• Lighting fixtures
• Photovoltaic panel covers

Packaging industries also utilize this standard when developing transparent films and containers that require specific light transmission properties.

Implementation and Best Practices

Proper implementation of ISO 13468-2 requires attention to sample preparation, environmental factors, and careful technique to ensure reliable results when measuring total luminous transmittance of transparent plastics.

Optimizing Sample Preparation

Sample preparation is critical for accurate measurements. Clean your specimens thoroughly with a lint-free cloth to remove any dust, fingerprints, or contaminants that could affect light transmission.

When cutting samples, avoid creating stress marks or scratches that might scatter light. A sharp cutting tool is essential to create clean edges.

For best results, samples should have parallel surfaces and uniform thickness. Ideally, prepare specimens between 1 mm and 10 mm thick, though thicker samples can be measured if your instrument allows.

Let specimens acclimate to the testing environment for at least 2 hours before testing to avoid temperature-related distortions.

Environmental Considerations

Temperature and humidity can significantly impact test results. Maintain a controlled laboratory environment of 23°C ± 2°C and 50% ± 5% relative humidity as specified in ISO 291.

Shield the testing area from direct sunlight and other bright light sources that might interfere with measurements.

Vibration can affect instrument stability, so place your spectrophotometer on a vibration-free surface.

Dust particles can scatter light and alter readings. Regularly clean the instrument and testing area to minimize contamination.

Keep the laboratory free from airborne contaminants that might settle on samples during testing.

Ensuring Accuracy and Repeatability

Calibrate your double-beam spectrophotometer regularly using certified reference materials. This ensures your baseline measurements remain consistent over time.

Take multiple readings at different points on each specimen to account for any material inconsistencies. A minimum of three measurements is recommended.

Position samples consistently in the instrument holder for each test. Even slight variations in placement can affect results.

Keep detailed records of all testing parameters including:

• Sample thickness
• Environmental conditions
• Instrument settings
• Calibration dates

Compare your results with those from ISO 13468-1 (single-beam method) periodically as a cross-check. Significant differences might indicate instrument issues.

Interpreting and Applying Test Results

The data collected from ISO 13468-2 testing provides valuable insights into material performance and quality. Proper interpretation of these results is essential for making informed decisions about material selection and product development.

Understanding Result Significance

Total luminous transmittance values obtained through ISO 13468-2 testing directly reflect how much visible light passes through the plastic material. Higher percentages indicate greater transparency, typically desirable for applications requiring optical clarity.

When interpreting results, consider the specific application requirements. For example, a 92% transmittance might be excellent for packaging but insufficient for precision optical components.

Test variability should be accounted for when analyzing results. Factors like specimen thickness, surface quality, and internal haze can influence measurements. Specimens thicker than 10mm can be measured but may not produce results comparable to standard thickness samples.

Remember that this test method applies specifically to transparent or substantially colorless plastics. Even faintly tinted materials can be evaluated, but heavily colored or fluorescent plastics require different testing approaches.

Case Study: Real-World Example

A manufacturer of display covers for electronic devices used ISO 13468-2 testing to compare three polycarbonate formulations. The results showed:

Material	Tjocklek	Total Luminous Transmittance
Formula A	2.0mm	89.5%
Formula B	2.0mm	91.2%
Formula C	2.0mm	90.3%

Formula B was selected for production despite its higher cost because the 1.7% improvement in light transmission significantly enhanced display brightness and readability.

The company also established a quality control threshold of 90% minimum transmittance. This benchmark ensured consistent optical performance across production batches. Any material falling below this threshold was rejected or relegated to non-display applications.

Implications for Product Design

Your product design can benefit greatly from understanding total luminous transmittance properties. Higher transmittance values generally correlate with better optical clarity and aesthetics in transparent applications.

Consider establishing minimum transmittance specifications based on your specific product requirements. Medical devices might require 92%+ transmittance, while general consumer goods might accept 85%+.

Material aging can affect transmittance over time. You should test aged samples to predict long-term performance, especially for outdoor applications where UV exposure occurs.

Remember that transmittance is just one property. Balance it with other material characteristics like impact resistance, chemical resistance, and processability when making final material selections.

Double-beam testing per ISO 13468-2 typically provides more accurate results than single-beam methods, particularly for quality-critical applications where precise measurements matter.

Comparison with Related Standards and Methods

Understanding how ISO 13468-2 relates to other testing standards helps laboratories select the most appropriate method for their specific application. Different standards offer various advantages depending on the material being tested and the required precision.

Comparison with ASTM Test Methods

ISO 13468-2 shares similarities with ASTM D1003, which measures haze and luminous transmittance of transparent plastics. However, ASTM D1003 uses a different light source and detection system than ISO 13468-2.

While ISO 13468-2 specifically uses a double-beam spectrophotometer, ASTM D1003 can utilize either a hazemeter or spectrophotometer.

Another related standard is ASTM E903, which measures solar transmittance and reflectance. This differs from ISO 13468-2 as it focuses on solar radiation rather than just visible light.

Key Differences:

• ISO 13468-2: Double-beam instrument, visible light range
• ASTM D1003: Can use single-beam, measures haze and transmittance
• ISO 13468-1: Single-beam instrument alternative

Advantages and Limitations

The double-beam system in ISO 13468-2 offers significant advantages over single-beam methods. It measures sample and reference simultaneously, minimizing errors from light source fluctuations.

Advantages:

• Higher precision for transparent materials
• Better compensation for instrument drift
• More accurate for slightly tinted materials
• Reduced influence of environmental factors

Limitations:

• Cannot be used for fluorescent materials
• Specimens thicker than 10mm may produce results that aren’t comparable with standard samples
• More complex equipment than single-beam methods
• Potentially higher cost of implementation

You should consider these factors when determining if this standard meets your testing requirements.

Selecting the Appropriate Standard

Your choice between ISO 13468-2 and alternatives should depend on your specific testing needs and available equipment.

Choose ISO 13468-2 when:

• You need high precision measurements
• Testing transparent or slightly tinted plastics
• You have access to a double-beam spectrophotometer
• Sample thickness is within recommended range (typically ≤10mm)

Select ISO 13468-1 (single-beam alternative) when:

• Lower precision is acceptable
• Equipment budget is limited
• Simplicity of operation is preferred

For materials with significant haze or diffusion properties, ASTM D1003 may be more appropriate as it specifically addresses these characteristics.

Remember that test results between different standards aren’t directly comparable, so consistency in method selection is important for benchmarking purposes.

Frequently Asked Questions

The ISO 13468-2 standard provides crucial guidelines for measuring total luminous transmittance in plastic materials using a dual-beam method. This testing protocol helps manufacturers ensure product quality and performance in various applications.

What is the purpose of the ISO 13468-2 standard in evaluating the total luminous transmittance of plastics?

ISO 13468-2 specifically measures how much light passes through plastic materials using a dual-beam method. This approach allows for precise quantification of a plastic sample’s ability to transmit light.

The standard helps manufacturers determine optical clarity and transparency, which are critical properties for many plastic applications. Products like display screens, window materials, and optical lenses rely on this data to meet performance specifications.

The dual-beam approach provides more accurate results by comparing the sample measurement to a reference beam simultaneously, eliminating many variables that could affect single-beam measurements.

How does the ISO 13468-2 test contribute to quality assurance in industries that utilize plastics?

This test method establishes a consistent way to verify optical properties across production batches. By regularly testing samples, manufacturers can quickly identify deviations in transparency that might indicate process problems.

The quantitative data from ISO 13468-2 testing creates objective pass/fail criteria for product acceptance. This eliminates subjective visual assessments and provides legal documentation of compliance with specifications.

For industries like automotive, electronics, and medical devices, the test confirms materials meet strict transparency requirements for safety and functionality.

Can you elaborate on the types of materials that are typically subject to ISO 13468-2 testing?

Clear or translucent thermoplastics like polycarbonate, acrylic, and PETG are commonly tested with this method. These materials are frequently used in applications where light transmission is essential.

Film products, including packaging materials and protective coverings, undergo ISO 13468-2 testing to ensure consistent optical properties. The test works well for thin materials that require precise optical characterization.

Specialty plastics used in optical components, lighting fixtures, and display technologies also rely on this testing standard. Any plastic where light transmission affects performance can benefit from this evaluation.

Why is the ISO 13468-2 standard considered a critical component in the production and assessment of transparent or translucent plastics?

The standard provides a globally recognized method that ensures consistency across manufacturers and countries. This facilitates international trade and collaboration in plastic production.

ISO 13468-2 testing detects subtle variations in light transmission that might be missed by visual inspection. These variations can significantly impact product performance in critical applications.

The test results help engineers predict how materials will perform in real-world lighting conditions. This predictive capability is essential for designing products with specific optical requirements.

What are the core principles that the ISO 13468-2 test is based on, and why are these principles important?

The dual-beam principle compares light passing through the sample to a reference beam simultaneously. This approach compensates for fluctuations in light source intensity and environmental conditions.

Spectral measurement across visible wavelengths (approximately 380-780nm) ensures comprehensive evaluation of transparency. This range matches human visual perception, making results relevant for applications where visual clarity matters.

The test uses precisely calibrated equipment to ensure reproducibility and accuracy. Standardized testing conditions allow for meaningful comparisons between different materials or production batches.

How do the results of the ISO 13468-2 test impact the development and application of plastic materials in various industries?

Test results guide material selection decisions for specific applications based on quantifiable optical properties. Designers can choose materials with confidence knowing exactly how they will perform optically.

Product development teams use transmittance data to refine formulations and processing methods. Small adjustments to additives or processing temperatures can significantly impact transparency.

Compliance with customer specifications often depends on meeting specific transmittance values. ISO 13468-2 test reports provide documentation for quality certification and customer acceptance.