大乘百法明門論開宗義決 1.12

1.12

證法光定者。謂於此中證希有定。能發智光照了法故。或云日光明定。從喻為名也。

Regarding "Realizing the Dharmaprabhāsa-samādhi": This means that herein he realized a rare samādhi, able to emanate the light of wisdom to illuminate and comprehend dharmas. Or it is called the Suryaprabhā-samādhi (Sunlight Samādhi), named after a metaphor.