I can't say it definitively, but I find it hard to believe the light would extinguish all that quickly given that the photo-electric sensors would still register smoke/steam from the smouldering material for a period of time after suppressant released into the compartment
I am of the same mind as Best Rate.
The photo-electric cells detect smoke apparently and also there is heat detection which is triggered at 110degrees C.
This from a -800 Engineering manual.
Functional Description
The filter drier meters the halon gas so that the halon level in the compartment stays above 3% for 195 minutes. The filter drier uses desiccant granules to remove moisture. It has a filter to remove squib debris or other contaminants to prevent line blockage.
So my question becomes;
Is 3% Halon detectable as smoke to the photo electric cells?
More thoughts please ( or better yet, a reference that says the light will extinguish).