*Disclaimer: As great as ambient light rejecting screen technologies are, there are still certain laws of physics that define what should and should not be done with a specialty material such as this.
Main Answer: Ambient Light Rejecting (ALR) projector screens are specially formatted to reject the majority of off-axis lighting from the top, bottom, and side angles. However if a strong light source is hitting the ALR material at roughly the same angle as the projector does, it will wash out the image. There is an easy solution. I strongly recommend light blocking curtains or blackout shades to shield your room and to rely on the interior lighting that ALR screens work with.