An easy to use vanilla JavaScript plug-in without production dependencies for displaying images, videos, or, through custom sources, anything you want in a clean overlying box.
Since 3.2.0 there are available custom attributes.
You can add srcset using data- prefix:
<a data-fslightbox="gallery" data-srcset="img/second.jpg 2x, img/third.jpg 3x" href="first.jpg"></a>
Especially on mobile it would be a performance advantage if the Lightbox would supports the img srcset and thus reduces the loading time for the user.