Glare on the Board: A Contrast Bound and the Price of a Curtain

A chalkboard beside an unshaded window can become unreadable at midday even in a bright room, because veiling glare adds light to chalk and board alike and crushes their contrast. This paper computes board contrast with and without stated veiling luminances, compares it with a stated legibility threshold, and prices a curtain as the fix. The finding is that brightness is not the problem: contrast is, and it is cheap to restore once named. Computed results: contrast_no_glare = 0.66, contrast_Lv150 = 0.21, contrast_Lv400 = 0.1, contrast_threshold_stated = 0.2, curtain_cost_usd = 18.0. Every number in this paper is produced by the accompanying script `compute.py`. SIMULATED, NOT MEASURED.