Default Backlight control file?

Hello, on my Onda v971 tablet, even the lowest screen backlight level seems a bit high for me especially in dark places. Therefore, I would like to know if there is a file that I could modify in order to lower the lowest backlight dimming level? Note that I have tried many screen filter applications but they are unstable on the ROM and they made the system quite slow when the filter is activated. Thanks.

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