Когда светофор станет зелёным, мы перейдём улицу.

When the traffic light turns green, we will cross the street.

Breakdown of Когда светофор станет зелёным, мы перейдём улицу.

• улица: the street
• мы: we
• когда: when
• светофор: the traffic light

Questions & Answers about Когда светофор станет зелёным, мы перейдём улицу.

Why does станет mean will become here?

The verb стать often means to become. In this sentence, светофор станет зелёным literally means the traffic light will become green.

That is a very natural way to say this in Russian, because Russian often focuses on the change of state:

• красный → зелёный
• не зелёный → зелёный

So the sentence is built around the idea when the light turns green.

Why is it станет зелёным, not будет зелёный or будет зелёным?

Because Russian is expressing a change, not just a state.

• станет зелёным = will become green / will turn green
• будет зелёным = will be green

For a traffic light, станет зелёным is more natural, because we are waiting for the moment when it changes color.

Also:

• будет зелёный is not correct here
• if you use быть, you would say будет зелёным, with the instrumental case

But even though будет зелёным is grammatically possible in some contexts, станет зелёным is the best choice here.

Why is зелёным in the instrumental case?