Lumens is a mesaure of light intensity, and it's what the light sensor is supposed to output in. I do use Lumos to manage the backlight though, and I was using it to tell me the values.

I don't mean the screen is harder to see when it's bright... I get that much.

What's happening though, is the light sensor is giving wrong values, which dims the backlight when it's bright out, the opposite of what I want. It is still hard to see but it dimming only makes it so much harder.