Try wearing a cap or hat with a peak to it as this may help to keep the daylight (sunlight?) from shine on to the screen.
Alternatively, try to build a small detachable cover over the top of the screen to shade it from the sunlight.
Also cut a small section ( 1 to 2 inches long) from an empty toilet roll and hold that over the screen when viewing. If that works then find something more substantial than a toilet roll that you can carry with you and use when the light is too bright.
Hope this helps.