Chromalight is a special lume material used by Rolex.
Chromalight is a proprietary luminescent material that Rolex claims lasts up to 8 hours.
Rolex introduced their proprietary Chromalight luminescent material in 2008 on the Rolex Deepsea, followed closely by use in the Rolex Submariner Date. Today it is used in the Rolex Explorer and Rolex Yacht-Master as well.