Optical Density Calculator
Calculate optical density, absorbance, and transmittance for light attenuation analysis
Optical Density and Absorbance Calculator
Intensity of light before passing through the medium
Intensity of light after passing through the medium
Optical Density Results
Formulas Used
OD = -log₁₀(I/I₀)
Optical Density
A = log₁₀(I₀/I)
Absorbance (Beer-Lambert)
T = (I/I₀) × 100%
Transmittance
A = -OD
Relationship
Interpretation
Light Attenuation: No attenuation (100% transmission)
Transmission Ratio: NaN
✅ No attenuation - material is completely transparent
Quick Examples
50% Transmission
OD ≈ 0.301
10% Transmission
OD = 1.000
1% Transmission
OD = 2.000
Example Calculations
Spectrophotometry Example
Scenario: UV-Vis measurement of sample solution
Incident intensity (I₀): 1.5 units
Transmitted intensity (I): 0.35 units
Calculation:
OD = -log₁₀(I/I₀) = -log₁₀(0.35/1.5) = -log₁₀(0.233) = 0.633
Absorbance = -OD = 0.633
Transmittance = (0.35/1.5) × 100% = 23.3%
Cell Culture Density
Scenario: Bacterial growth measurement
Incident intensity (I₀): 0.80 units
Transmitted intensity (I): 0.10 units
Calculation:
OD = -log₁₀(0.10/0.80) = -log₁₀(0.125) = 0.903
Result: High bacterial density with 12.5% transmission
Optical Density Scale
Applications
Spectrophotometry
Quantifying nucleic acids, proteins, and other biomolecules in solution
Microbiology
Measuring bacterial growth and cell density in cultures
Environmental
Water quality analysis and pollution monitoring
Biomedical
Blood analysis and clinical diagnostics
Materials Science
Optical properties of films and coatings
Understanding Optical Density
What is Optical Density?
Optical density (OD) is a measure of how much light is attenuated (reduced) when it passes through a material. It quantifies the material's ability to absorb, scatter, or otherwise reduce the intensity of transmitted light. Higher optical density means more light attenuation.
Key Properties
- •Dimensionless: OD has no units as it's a logarithmic ratio
- •Logarithmic scale: Each unit represents 10× change in transmission
- •Additive: OD values can be added for multiple layers
- •Wavelength dependent: OD varies with light wavelength
Mathematical Relationships
OD = -log₁₀(T)
T = I/I₀
A = -OD = log₁₀(I₀/I)
Beer-Lambert Law
A = ε × c × l
- A = Absorbance
- ε = Molar extinction coefficient
- c = Concentration
- l = Path length
Optical Density vs. Absorbance
Optical Density
- • Measures overall light attenuation
- • Includes absorption, scattering, reflection
- • Used in general optical applications
- • OD = -log₁₀(T)
Absorbance
- • Measures only light absorption
- • Specific wavelength measurements
- • Used in analytical chemistry
- • A = log₁₀(I₀/I) = -OD
Practical Applications
Laboratory Analysis
- • DNA/RNA quantification
- • Protein concentration
- • Enzyme activity assays
Quality Control
- • Food and beverage analysis
- • Pharmaceutical testing
- • Environmental monitoring
Medical Diagnostics
- • Blood analysis
- • Urine testing
- • Tissue imaging