How drawing in stormlight works(I think)

[Karger]

With Navani's lecture on fabrail construction I think we have some clues on what is happening when a radiant draws in stormlight.  During her lecture Navani explains the Arnist Method

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Several large empty gemstones are brought close to the infused one while the spren is inspecting it. Stormlight is slowly absorbed from a small gemstone by a very large gemstone of the same type—and several together can draw the Light out quickly...

This seems fairly similar to how a radiant sucks stormlight from gemstones.  However for it to happen in an identical manner humans there would have to be some other form of displacement.  Basically the radiant would have to temporarily shrink of move their soul from their body.

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Argent

Do deadeyes disappear in Shadesmar when they are summoned as blades to the Physical Realm?

Brandon Sanderson

Yes, mostly.

JordanCon 2018 (April 21, 2018)

Spren only appear fully in the PR when they don't appear fully in the cognitive.  To do this radiant spren bond humans.  I think when drawing in stormlight radiants are doing the reverse.  The spren is drawing the radiant's soul into the cognitive and perhaps spiritual realms(more on this in a bit).   The stormlight moves to inhabit the radiant's body and can be commanded by the radiant using the talents of the spren(gained through spirit web intertwining).  This is supported by Kaladin catching a sight of the cognitive realm while training in the chasms. 

As a radiant progresses through oaths they gain increased abilities.  It seems reasonable that they pull themselves further thus gaining an increased ability to draw on larger amounts of stormlight.  It also explains what bondsmiths do when charging radiants.  A bondsmith spren is much more powerful and spiritually oriented then a normal true spren.  As such they can move a bondsmith's soul a bit into the spiritual realm thus opening a partial perpendicularity that charges the radiant.  Dalinar can go the full way(because of the Stormfather's new Honor derived powers) allowing him to open a full perpendicularity.  This might also explain why Jasnah say that holding too much stormlight is not good for a radiant(OB).  The body and soul of the radiant could become dependent on the constant influx(we see this with savantism).  It also explains why Dalinar finds opening the portal so tiring.  He is straining the bond between soul and body.  I worry that if he tries to hard he might break it.