Corrected entry: The children's condition is called Xeroderma pigmentosum, according to a special feature in the DVD. When first bringing Mrs. Mills to meet the children, Grace explains that the children are photosensitive and cannot bear light much stronger than that emitted by the lamp she is carrying. Xeroderma patients are sensitive to ultraviolet light, a certain kind of light (wavelength, and not the intensity (amplitude) of the light. The children should be able to bear a strong light like anyone else so long as it is not UV.
JC Fernandez
13th Aug 2009
Correction: Firstly, the film takes place in the late 1940s, you would hardly expect a layman of that era to fully understand the distinction of ultraviolet light. Secondly, the film establishes Grace as mentally unbalanced and prone to hyperbole. Finally, the whole "world" Grace lives in is a fantasy. The rules could be whatever her mind sets it to be.
JC Fernandez