Yeah, that's the question. In university docs I found the Argand Lamp to be a gas lamp, but in all online references so far it's oil-based. The painter could have applied too much artistic license for effect, but the gas/oil discrepancy needs sorted. Looks like oil has the upperhand.
Argand...
The Utrechtse Academie was the main fraternity of Utrecht University. The text states that the male students paid for this painting. The lighting most likely consisted of the Argand Lamp or 'English Lamp', a gas light.