Absorbance and transmittance are two related but opposite ideas in spectrophotometry.
Here’s the difference explained:
1. Meaning
- Absorbance shows how much light is absorbed by the sample.
- Transmittance shows how much light passes through the sample.
2. Behavior
- If a sample absorbs a lot of light, its absorbance is high and transmittance is low.
- If a sample absorbs little light, its absorbance is low and transmittance is high.
3. Values
- Transmittance (T) is expressed as a percentage (%T), from 0% to 100%.
- 0% T → no light passes through.
- 100% T → all light passes through.
- Absorbance (A) is usually a number without units, often between 0 and 2 for most samples.
4. Relationship
- They are mathematically related:
When transmittance decreases, absorbance increases.
5. Simple Example
- Clear water: High transmittance, Low absorbance.
- Dark solution: Low transmittance, High absorbance.
In short:
- Absorbance = how much light is taken in by the sample.
- Transmittance = how much light passes through the sample.