Bro you should cover that side of the enclosure or paint it black. Light can't naturally penetrate a burrow in the wild and you can't naturally see into a burrow in the wild so that observational window there is just serving the owner not the tarantula. You should really cover it bro.Better for who? Your captive animal or its owner....This is nothing but a selfish thought that serves only the owner. I have Ts that burrow and I'm able to monitor their health, as best as a human can do, considering we know very little about them to begin with.
I think someone who is TRULY interested in Ts should/would foster/provide as much opportunity to see the T go about its natural behavior and actually ENJOY its natural life cycle (as much as one can in a captive setting) rather than just sit there and stare at their T because they thought it was pretty.
I'll use my I. mira as a perfect example. I find this species to be quite beautiful, golds with some black contrast and bright blue tipped front legs. I could stare at that all day, and certainly could if I provided no sub. This species is an obligate burrower, living its trapdoor life and rarely coming to the surface. I've seen mine come to the surface 2 so far, 1 last night. I love when s/he does of course. However, I find it far more fascinating to observe this animal when it's in its burrow w/its trapdoor. I'm able to watch it stalk prey from below "ground". I can see how sensitive it is to different size prey that are on the surface. I've observed how it makes the trap door quite a few times, and whether it hunts right side up, or upside down while in its tunnels. It's all far more fascinating than just sitting there and watching s/he out in the open.