When a Wraith initially loses insubstantial from Radiant damage does it take full damage?

Question

In a recent battle I was DMing when the players were cleansing the temple in Gardmore Abbey, the players were attacked by a Trap Haunt which is a very wraith-like creature.

Wraiths are usually insubstantial and they usually lose that insubstantial trait when they are exposed to Radiant damage.

Insubstantial
The [wraith creature] takes half damage from all attacks, except those that deal force damage. Whenever the [wraith creature] takes radiant damage, it loses that trait until the start of its next turn.

But that begs the question, do Wraiths take full radiant damage from the initial hit, rather than half?

Answer 1

No.

As Colin pointed out, it's taking radiant damage that causes it to lose insubstantial. Since losing insubstantial is not an Immediate Interrupt, it does not occur before the event that triggered it, but after it.

Basically, force attacks bypass its insubstantiality, radiant attacks help other attacks bypass its insubstantiality.