They decided to use a different source for background light.

他们决定使用不同的光源作为背景光。

You need that light background for the pupil to work appropriately to minimize the amount of light coming in.

为了让瞳孔缩小，减少进入眼睛的光线，你就需要有一个明亮的背景。

You need that light background for the pupil to work appropriately to minimize amount of light coming in.

您需要明亮的背景让瞳孔正常工作，以最大程度地减少进入的光量。