I don't think it's as simple as an edit of build.prop. I did a quick search in /system and it appears that /system/etc/flashled_calc_parameters.cfg contains some values that configure the flash led brightness.
Like this -
# LED If setting for Torch or video recording (uA).
if_torch_vr = 62500
I'm not going to alter any of them though, as
1. I don't even know if it's the correct file to begin with.
2. I don't know the safety thresholds for our devices LED and
3.I don't feel like having to recover my device from a bootloop on a Sunday afternoon if something goes wrong.
Maybe somebody that knows more about these things will come along and help.
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