His heart was so light that he felt he could fly.

他的心情是如此的轻松，他觉得自己可以飞起来了。

youdao

If you must fly, be sure to pack light to cut down the plane's load.

如果你必须坐飞机，一定要轻装上阵，减少飞机的载重。

youdao

Fireflies give off flashes of light when they fly at night.

萤火虫夜间飞行时发出闪光。

《新英汉大辞典》

That speed and flexibility allowed us to easily adjust to varied light settings on the fly as we went from indoor to outdoor shooting locales.

ENGADGET: Sony Alpha NEX-6 sample shots and video Hands-on

Wind noise was readily audible when filming outside, but the color reproduction was quite accurate, and the RX1 adjusted to varying amounts of light quickly on the fly.

ENGADGET: Sony Cyber-shot RX1 sample images and video Hands-on

Insect eyes differ fundamentally from animal eyes: the fly focuses light over a large radius through hundreds of separate facets, while animals focus it over a smaller radius through a single lens.

ECONOMIST: Genetic science