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。

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。

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。