Shardplate Theory

[A Windspren he/him]

Shardplate is powered by gemstones with Stormlight. When Kaladin uses a Shardplate helm as a glove, it drains away his Stormlight. What if when the Radiants used Shardplate, it ran on the Stormlight in their bodies? Shardplate might even be able to store Stormlight inside it, hence the glow Dalinar sees in his visions.

[The Honor Spren she/her]

You're not the first one to come up with this theory.