ASTM E1348 Transmittance and Color by Spectrophotometry Using Hemispherical Geometry
ASTM E1348 explains the use of a spectrophotometer or spectrocolorimeter with a hemispherical optical measuring apparatus, such as an integrating sphere, to measure the transmission characteristics and color of object-color specimens. The value stated in SI is considered as standard.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM E1348 establishes a standardized method to measure transmittance and color of transparent and translucent materials using spectrophotometry with hemispherical geometry. It evaluates how much light passes through a material and how the transmitted light influences perceived color under controlled conditions.
The method is essential for characterizing optical properties of materials such as plastics, glass, films, and coatings. By using an integrating sphere, it captures total transmitted light, including diffuse and scattered components, ensuring accurate and reproducible measurement of color and transmittance for quality control and research applications.
Scope, Applications, and Benefits
Scope
ASTM E1348 covers the measurement of total transmittance and transmitted color using hemispherical (integrating sphere) geometry. It applies to transparent, translucent, and semi-transparent materials.
- Measurement of total spectral transmittance
- Determination of transmitted color using spectrophotometry
- Applicable to transparent and translucent materials
- Use of integrating sphere for total light capture
- Evaluation under standardized illumination conditions
Applications
- Optical plastic and film characterization
- Glass and glazing transmittance testing
- Packaging material transparency evaluation
- Automotive window and display materials
- Coating transparency and tint evaluation
- Research in optical material development
Benefits
- Provides accurate measurement of light transmission
- Ensures consistency in optical and color properties
- Supports quality control and compliance requirements
- Captures both diffuse and direct transmitted light
- Enables precise color formulation for transparent materials
- Improves material selection for optical applications
Testing Process
Instrument Setup
Use a calibrated spectrophotometer equipped with an integrating sphere for transmission measurements.
1Instrument Calibration
Perform wavelength and photometric calibration using defined reference standards as specified by the instrument manufacturer.
2Selection of Measurement Conditions
Select the required illuminant, standard observer, wavelength range, and measurement interval based on the test requirement.
3Data Recording & Reporting
Report transmittance values, color data, instrument settings, and test conditions, including any deviations from the standard.
4Technical Specifications
| Parameter | Details |
|---|---|
| Optical Geometry | Hemispherical (integrating sphere) transmission |
| Applicable Materials | Transparent and translucent solid materials |
| Wavelength Range | Visible spectrum (typically 380–780 nm) |
| Observer Angle | Standard observer (2° or 10°) |
| Specimen Placement | At the transmission port of the integrating sphere |
| Instrument Type | Spectrophotometer or Spectrocolorimeter |
| Reporting Requirements | Instrument settings, measurement conditions, and results |
Instrumentation Used
- UV–Vis spectrophotometer
- Integrating sphere (hemispherical geometry)
- Calibrated color and transmittance standards
- Sample holder or mounting stage
- Stable light source
- Data acquisition and color analysis software
Results and Deliverables
- Total spectral transmittance values
- Transmitted color coordinates
- Spectral transmittance curves
- Optical clarity and tint data
- Calibration and measurement report
- Quality control and compliance documentation
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Frequently Asked Questions
Total transmittance refers to the amount of light that passes through a material, including both direct and scattered light. It provides a comprehensive measurement of how transparent or translucent a material is under standardized spectrophotometric conditions.
Hemispherical geometry ensures that all transmitted light, including diffuse scattering, is captured. This eliminates directional bias and provides a more accurate representation of a material’s true optical transmittance and color properties.
Unlike direct methods that measure only straight-line transmitted light, ASTM E1348 captures total transmitted light using an integrating sphere. This includes scattered and diffuse components, making it more accurate for translucent and complex materials.
Factors include material thickness, surface finish, internal structure, and pigmentation. Even minor variations in sample preparation or environmental conditions can affect light transmission and result in measurement deviations.
Absorbance and transmittance are inversely related. As a material absorbs more light, less light is transmitted. This relationship is fundamental in interpreting optical properties.
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