Transmission is typically measured by comparing the amount of light that passes through a material to the amount of light that was incident on the material. This measurement procedure generally consists of two key steps.
The Two Steps of Transmission Measurement
According to standard procedures, measuring transmission involves a direct comparison between the original light source and the light that makes it through the object being tested.
Here are the fundamental steps:
- Collecting a Baseline: This involves measuring the reference standard light source without the object or material in the path of the light. This step establishes the initial intensity or amount of light being used. It acts as the 100% reference point.
- Measuring with the Object: The object or material whose transmission is being measured is placed in the path of the light, and a second measurement is taken. This records the amount of light that successfully passes through the material.
By comparing the second measurement (light through the object) to the first measurement (baseline light), you can determine the fraction or percentage of light that was transmitted.
Why These Steps Are Crucial
- Establishing a Reference: The baseline measurement (Step 1) is essential because it accounts for the intensity of the light source itself and the characteristics of the measurement setup before the material is introduced.
- Isolating the Material's Effect: The measurement with the object (Step 2) shows how the material specifically affects the light – how much it absorbs, reflects, or scatters, leaving only the transmitted portion.
Calculating Transmission
Once the two measurements are taken, transmission (often denoted as T) is calculated as the ratio of the transmitted light intensity ($I_t$) to the incident light intensity ($I_0$):
$T = \frac{I_t}{I_0}$
Where:
- $I_t$ is the intensity measured with the object (Step 2).
- $I_0$ is the intensity measured without the object (Step 1 - the baseline).
This ratio is often expressed as a percentage by multiplying by 100%.
Practical Application
This two-step method is fundamental in various fields, including:
- Optics: Measuring the transparency of lenses, filters, or windows.
- Material Science: Characterizing the properties of films, coatings, or liquids.
- Chemistry: Using spectroscopy to analyze the concentration of substances based on light absorption/transmission.
| Measurement Step | Description | Purpose |
|---|---|---|
| Baseline (Step 1) | Measure light source without the object. | Establish 100% incident light reference |
| Object (Step 2) | Measure light source with the object in path | Measure transmitted light |
In summary, transmission is measured by first establishing a baseline of the light source and then measuring the light after it has passed through the material, using these two values to calculate the transmitted fraction.
