Joining a worldwide, daily call for applause and gratitude for the healthcare workers on the frontlines of the COVID-19 pandemic, the top of Salesforce Tower was illuminated this week with a video of clapping hands.

Video artist Jim Campbell, who is responsible for the looping videos that have played across the tower's crown since the building opened two years ago, decided the eight-story LED-powered "screens" needed a refresh now that his most recent work, titled "Day for Night," had gone idle. As he explains to the Chronicle, the videos that have been playing on the tower top for the last nine months — which launched last July — were street scenes captured from several locations around the city. And now that the streets are empty, these images had become pretty boring, and depressing.

He began with images of a globe, and of swaying trees in Golden Gate Park.

"The globe was to suggest that we are all in this together," Campbell tells the Chronicle, "and the trees were to show that people could get out of their houses even when stuck in their houses."

But then his studio assistant suggested they add the clapping hands, inspired by videos like the one below, circulating on the internet, of nightly rounds of applause in various cities around the world for doctors and nurses caring for the sick — and often getting sick themselves.

Campbell's assistant, Emma Strebel, then solicited 10-second video clips from friends and family of their disembodied hands clapping, and the sequence now playing nightly on top of Salesforce Tower is the result.

The clapping hands began appearing Tuesday night, along with an accompanying video of prayer flags blowing in the wind.