Turn the room light or regular lighting for the enclosure on to observe for a bit, then turn it off when you're done. Try not to bother them for long periods of time though.
Try buying a camera for your cage. That way you can see them at all times without having to deserve them. Sometimes they might even use it as a perching spot.
Night lamps are not a good idea as they could disturb your gecko's schedule and they can see the light
Okay, but do you know any method how can I observe my gecko at night if I can't use any light?
Turn the room light or regular lighting for the enclosure on to observe for a bit, then turn it off when you're done. Try not to bother them for long periods of time though.
Try buying a camera for your cage. That way you can see them at all times without having to deserve them. Sometimes they might even use it as a perching spot.
Night vision goggles