Google introduced a brand new advertising format today that clients pay for based on engagement.

The format, called Lightbox, initially appears as a regular display ad somewhere within a webpage. However, two seconds after a user hovers over the ad, it expands into a large canvas in the center of the page, leaving everything outside of the canvas shaded dark. It’s sort of like what you see when clicking on a Facebook picture, except you’re getting an advertisement.

Based on internal testing from Google, the “Smarthover” method of triggering a Lightbox ad eliminates the majority of accidental ad expansions and increases engagement significantly over standard click-to-expand ads.

The company sees this as a win for marketers, who get a better sense of who is actually interested in an ad and only pay when a user expands the lightbox.

The Lightbox format is the first in a new family of ads, according to Google Vice President of Brand Solutions Jim Lecinski, who spoke at the AdvertisingWeek event today.

Google isn’t the only ad company that’s moving away from the traditional pay-per-click display ad spots. Facebook recently published a study showing that clicks don’t prove that users are actually engaging with ads.