Two sources of illumination must differ by  between 5 to 10% to be detected.

两个照明源必须相差 5% 到 10% 才能被检测到。

Households that could not afford really nice sources of illumination would use lamps that burned the oil from baleen whales, which wasn't as nice.

买不起优质照明源的家庭会使用燃烧须鲸油的灯，但效果不太好。

The one tiny window was the only source of illumination, and the light that came in fell on a family of five.

那一扇小小的窗户是唯一的照明源，射进来的光落在一家五口的身上。