If the light is too dark, it will affect people's eyesight.

光线太暗会影响视力。

youdao

Turn on the light because it is too dark to see.

太暗了看不见，把电灯打开。

youdao

This jacket is too dark.

这件上衣颜色太老了。

《新英汉大辞典》

She is easily frightened. For example, she is too chicken-livered to walk down a dark street alone at night.

VOA: special.2010.06.13

The data might be used to determine, for instance, whether a particular aisle is too dark or cumbersome or whether products are placed too or too low.

FORBES: Why Stalking Your Customers Via Their Mobile Phones is Not a Good Idea

This will allow the virtual display to show things such as weather and other aeroplanes, further increasing the pilot's awareness when it is too foggy or dark to see outside.

ECONOMIST: MONITOR

Or perhaps everyone is too much in the dark to react.

BBC: Boston bombing: A changed US reaction to terror