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can somone help me understand exposure a little bit better?

lets say its a nice sunny day and I am using 100 speed film with my camera set to shutter priority and its set for 1/125th of a second. I’m taking a picture of a solid WHITE wall..dont ask me why..and the aperture reads f16. Now, If I go ahaed and snap the picture, I would like someone to explain to me, in pretty understandable terms as to whether the pic will turn out under or over exposed..and why?? I am missing a key understanding of this concept and my pictures are sufffering because of it.

If that is what your camera meter is reading most likely the photo will be underexposed. Typically when photographing excessive amounts of white you want to overexpose by at least 1.5-2 stops or if you do not have a overexposure compensation setting on your camera set the ISO to 32 if you are using 100 ISO film.
To understand why a cameras light meter will almost always underexpose an image with excessive white areas, you have to understand how cameras a light meter works. A camera’s light meter is programmed to believe that the perfect photo is a middle gray color. So when you point your camera at a white wall the meter says that it should make that white wall a middle gray color but in order to do this it would has to underexpose the image. Vice versa if you point a camera at a black wall the meter will think, this black wall should be a middle gray color and consequently give you a setting which will make that image a middle gray, hence it will overexpose the image.
The solution is to either purchase a handheld incident light meter, or purchase and learn how to use a gray card(cheap solution)

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