As a rule, "normal" interior doors do not fulfil any requirements for tightness, sound, fire or smoke protection.
It regularly happens that light passes through such doors in the rebate area. This is not a defect in normal interior doors, as there are no requirements for tightness - neither standardised nor by law.
The rubber profiles often referred to by consumers as "seals" are standardised "damping profiles" (see DIN 68706-2, No. 3.8 and 3.9). The damping ensures that the door leaf does not hit directly against the frame when closing, as used to be the case. The aim: the closing noise of the door is dampened by the profile. Cushioning profiles do not make the door system leak-proof.
Consequently, the door can be "leaky" - whether for air or light is irrelevant.
It is not uncommon for light-coloured or transparent damping profiles to be used (or also sealing profiles). The colouring or lack of colour can cause the plastic profile to "glow". This effect cannot be classed as a defect either - unless this has been contractually excluded (note: then use dark-coloured profiles if possible).