What Im thinking is, whoever is wroking on the ride "settings" so to speak is probably in that dark building for extended periods of time, so there eyes have plenty of time to adjust, & set the screens brightness accordingly thinking it looks good enough, wheras its a totally different story for the average park guest who is outside where the bright sun makes your eyes pupils de-dialate, & than suddenly stepping into a dark environment, & there eyes not having much time to re-dialte & adjust, resulting in percieving the screens to be darker than they actually are. As quirky as it sounds, when I go through the line, I close my eyes as much as I can so my pupils can dialate faster so I can see better, & it actually does make it easier to see.
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I also do this whenever I ride Mummy.