# Beer Lamber Law scaling

**URL:** <https://mne.discourse.group/t/beer-lamber-law-scaling/8910>\
**Category:** Support & Discussions\
**Tags:** preprocessing, fnirs\
**Created:** [June 6, 2024, 11:42pm UTC](https://mne.discourse.group/t/beer-lamber-law-scaling/8910 "2024-06-06T23:42:39Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Gautam-Bala](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/gautam-bala/32/3711_2.png) [@Gautam-Bala](https://mne.discourse.group/u/Gautam-Bala)\
**Post date:** [June 6, 2024, 11:42pm UTC](https://mne.discourse.group/t/beer-lamber-law-scaling/8910/1 "2024-06-06T23:42:39Z")

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Hi All,

Can someone suggest on what basis a scaling factor of 1e-3 is applied to Beer Lambert Law calculations in MNE and would it differ for infants?

Reference: Line 76:

raw.\_data[[ii, jj]] = iEL @ raw.\_data[[ii, jj]] \* 1e-3

[mne-python/mne/preprocessing/nirs/\_beer\_lambert\_law.py at maint/1.7 · mne-tools/mne-python (github.com)](https://github.com/mne-tools/mne-python/blob/maint/1.7/mne/preprocessing/nirs/_beer_lambert_law.py#L21-L89)

Thanks,  
Gautam

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**Author:** ![yslbit](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/yslbit/32/3926_2.png) [@yslbit](https://mne.discourse.group/u/yslbit)\
**Post date:** [October 12, 2024, 1:18am UTC](https://mne.discourse.group/t/beer-lamber-law-scaling/8910/2 "2024-10-12T01:18:09Z")

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this is to keep the unit with mM, while, I have a question about the delta A, how to compute it