Modelling an LED source vs laser - equivalent power, profile and unit conversion
Emillie Jo
- What exactly is the unit of the fluence map (.mc2) values in x, y and z?
- Is each inputted photon weighted equally (weight = 1 per photon)? - with the fluence data being the total photon weight deposited per voxel.
- To scale results, is it correct to multiply each voxel fluence value (x, y, z) by the energy per simulated photon
(
/
) where:
Qianqian Fang
see replies below
(Part of this question connects to my other post titles: Understanding fluence map output for modelling a source-detector separation problem).
Hello,
I'm trying to model an LED light source in MCX studio for a skin-illumination setup. These are the light sources I want to replicate:
Through literature reading, I have found that the zgaussian source type in MCX studio most closely resembles an LED's Lambertian emission profile, but is this the best choice? Is there a better way to model an LED beam distribution?
use user-defined launch angular distribution gives you most
flexibility and accuracy, see help info and example
https://github.com/fangq/mcx/blob/v2025.10/mcxlab/mcxlab.m#L132-L150
however, I don't know if it can make much of a difference
compared to a zgaussian src fitted to your LED emission profile,
but feel free to compare the two approaches
Photon energy weighting - relating fluence maps to real optical power and MPE:
Since MCX uses photon number rather than optical power as input, I want to confirm the correct way to scale fluence map data to physical units (J/mm^2 or mW/mm^2) when modelling an LED source.
- What exactly is the unit of the fluence map (.mc2) values in x, y and z?
for the output unit question, please checkout this previous reply
https://groups.google.com/g/mcx-users/c/IGHXbEpHF5Q/m/-QVdk9QvCAAJ
as well as
https://groups.google.com/g/mcx-users/c/dH4OlY1NG6M/m/qGusJOakBgAJ
- Is each inputted photon weighted equally (weight = 1 per photon)? - with the fluence data being the total photon weight deposited per voxel.
no, they are weighted individually
- To scale results, is it correct to multiply each voxel fluence value (x, y, z) by the energy per simulated photon (
/
) where:
=
*
-> determined from an LED datasheet, converted from mcd -> mW
-> simulation time defined in MCX studio
because MCX's normalized solution (default) is the impulse
response (of a unitary source), whatever your real source's
power/energy can be multiplied to the output to scale to your
desired source strength unit, whether it is power or energy.
Many thanks,Emillie Jo
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