When to use
- Planning fiber optic placement depth for optogenetics experiments
- Estimating minimum laser power needed for a target depth
- Comparing activation volumes across fiber configurations
- Checking whether your setup risks photothermal damage
ToolsConductScience tool
OptogeneticsFree in-browser calculator
Optogenetics Irradiance Calculator.
Estimate light penetration depth and irradiance in brain tissue for optogenetics fiber placement planning. Modified Beer-Lambert model with tissue-specific scattering coefficients.
PrivateData stays in your browser
LiveNo sign-up required
Validated2026-04-08
CitableMethods and citation included
Calculator
Results update in placeWavelength
Fiber & Power
Brain Region & Opsin
Results
- Peak irradiance
- 159.15 mW/mm\u00b2
- \u00b5eff
- 1.525 mm\u207b\u00b9
- Spread angle
- 16.7\u00b0
- Wavelength
- 473 nm
\u26a0 Heat Warning
Peak irradiance (159.2 mW/mm\u00b2) exceeds 75 mW/mm\u00b2. Risk of photothermal tissue damage.
Irradiance vs Depth
Do not use for
- As a substitute for in vivo power measurements
- For modeling complex 3D light distributions (use Monte Carlo)
- For two-photon optogenetics power estimation
Measure at the tip
Fiber coupling losses can be 30-50%. Always measure power at the fiber tip, not the laser source.
Red light goes deeper
Switching from 473 nm to 635 nm with red-shifted opsins (Jaws, ReaChR) can double penetration depth.
Heat is the hidden confounder
Photothermal effects can mimic optogenetic activation. Use opsin-negative controls and keep irradiance below 75 mW/mm².
NA matters more than you think
A 0.22 NA fiber produces a tight pencil beam; 0.50 NA spreads into a wide cone. The effective volume changes dramatically.
1
Method
Modified Beer-Lambert law with geometric beam spreading. Tissue optical properties at 473 nm from Aravanis et al. 2007 and Yizhar et al. 2011. Wavelength correction via power-law scaling of scattering and absorption.
2
Validated
Last validated 2026-04-08. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
3
How to cite
How to Cite
ConductScience Optogenetics Irradiance Calculator (v1.0). ConductScience, Inc. 2026. https://conductscience.com/tools/optogenetics-irradiance-calculator
Aravanis AM et al. J Neural Eng. 2007;4(3):S143-S156.
Yizhar O et al. Neuron. 2011;71(1):9-34.
Stujenske JM et al. Cell Reports. 2015;12(3):525-534.
Modified Beer-Lambert Model
This calculator uses a modified Beer-Lambert model with geometric beam spreading:
I(z) = (P / (π × r(z)²)) × exp(-µeff × z)
- r(z) = r₀ + z × tan(θ) accounts for the expanding cone of light
- µeff = √(3 × µa × (µa + µs')) is the effective attenuation coefficient
- θ = arcsin(NA / n_tissue) is the half-angle of the fiber's acceptance cone
This is a standard approximation used in optogenetics literature (Aravanis et al. 2007, Yizhar et al. 2011).
Practical Fiber Placement Tips
Key considerations:
- Place fiber tip 200-300 µm above target region to account for tissue displacement
- Measure power at the fiber tip after implantation cannula coupling
- Use power meter readings, not laser source settings
- Consider backscatter at the fiber-tissue interface (not modeled here)
- For bilateral stimulation, use separate fibers rather than higher power
Frequently asked
325
Free tools
1,200+
Institutions
100%
Client-side
0
Uploads required