As soon as Jackson and Sammy had fallen through the floor they were met with an endless darkness. "We are fine, just find the key to the basement!" Jackson and Sammy were sure that Jane and Asher would be able to get them out.
"The door to the basement said freedom, right? That should mean the exit is down here. So we might have gotten lucky." Jackson was trying to think on the more positive side of things since he knew that Sammy was worried about the darkness. However, he was also shocked to find that he was not able to see as well.
This wouldn't make much sense, but Jackson had a super power that enhanced his body to the pique of humanity. This meant that he had better vision than most people. For there to be a place with so little light that even he thought it was dark then that would mean Sammy was in the pitch black emptiness with only his voice.