If one's going to be able to read it when it's in direct sunlight, the display has to be pretty bright

well, this is not so 'new', How often have we seen someone with "I have this thing that works, now I want to add ..."

Then the fundamental shortcoming in the initial design comes out but the argument continously is "if it works here it must be able to work there, I will make it work, just tell me how".

The LED activation (current * time) between night (~ indoor) and day is, at least 1:30 so, of course, any design (such as heavy MPX) that produces a cute little slightly dim sign will work great indoors, but not have a chinaman's chance outdoors.

Erik