פירוש על נגעים 2:3

אין פותחין לו חלונות – as it is written (Leviticus 14:35): “Something like a plague has appeared [upon my house]”/"כנגע נראה לי [בבית]" – to me but not to my light (i.e., the Lord’s light), from here they (i.e., the Sages) said: In a dark house, they don’t open for him the windows.

A priest who is blind in one eye or the light of whose eyes is dim should not inspect negaim; for it says, "Wherever the priest's eyes can see" (Leviticus 13:12). The priest must have two fully functioning eyes in order to examine negaim.

In a dark house one may not open up windows in order to inspect his nega. A "dark house" is a house that doesn't have any windows. One should not open up new windows in such a house in order to examine a nega. However, Albeck notes that if a house already has windows, they may be opened to examine the nega.