The % of brightness is controlled by coding the option. This requires either the aftermarket android stereo with the ibus adapter like semcoinc mentioned or using a notebook computer and ncs expert type of tools to program them to a different brightness level.

Changing the bulb may effect brightness somewhat but the % of power going to the bulbs (the real brightness determining factor) has to be adjusted by coding.

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Just BMW's - All cars and trucks was two pages long
1994 318is
1997 528i
2000 323i
2001 X5 3.0 auto
2005 X5 3.0 auto
2011 535xi auto
2013 X5 xdrive35 Turbo
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Aftermarket E53 Radio Install