Lightbox is a standard ad unit that expands into a large canvas in the center of the page, leaving everything behind it dark. Through this method, you will only pay when the ad is expanded, not click.
To combat accidental expansions, Lightbox will only activate if an individual hovers over it for at least two seconds. Google’s internal testing found that the “smarthover” method also increased engagement significantly over standard click-to-expand ads.
According to Google Vice President of Brand Solutions Jim Lecinski, the Lightbox format is the first in a new family of display ads which focus on engagement. It will also support a variety of content, including photos, YouTube videos, shopping experiences, and more.
The new ads are currently being tested with a “handful” of advertisers, but are expected to rollout “soon.” It appears that Lightbox will first be available online with mobile support to follow. You can learn more about Lightbox on Google’s blog.