Perhaps it didn't help much, but at least most TOTL arrangers have a tilt screen, that would allow you at least to avoid a direct reflection of the sun.

However, in the opposite environment, like really dark lighting conditions. I have found the Tyros series and lit buttons to work out quite well to operate. If anything, maybe sometimes too bright, but I really love the tempo button flashing with the orange light keeping measures on time. This visual cue has helped me in many occasions and in less then desirable sound and light environments to get me back on track to the proper timing.

Marcus