I recommend green #3 safety glasses (after testing a handful of safety glasses of different shades). Green #3 is dark yet light enough to enable you to see the firing chamber.
During a recent test firing, I pointed a bright LED flashlight into a kiln at around 1800F. (Someone else lifted the lid for me.) That flashlight is so bright that the rest of the kiln was dim by comparison. I haven't yet pointed the flashlight into a peephole. (The test kiln in my office is very small and doesn't have a peephole).
To get a wide view through the tapered peephole, you have to move your head from side to side. If you need to place the cones close to the peephole, put a bent cone on the shelf and position it where you can see the tip. Use that as a guide in positioning a straight cone. If the straight cone is too low, the tip will disappear when the cone bends.
You're not alone. Surgeons write with a felt-tip marker on the limb to be operated on to make sure they work on the correct one. And I've heard of two other cases where a technician came out to work on a kiln, only to find that it was unplugged.
How much space it too much, when lid warps. Will flipping lid help. My lid sets pretty well when cold, but develops a lot of space when firing. I know some space is ok, but mine looks abnormal, over 1/4" in places. Is there a high temp blanket that would help with this?
The center of the lid bows slightly inward toward the firing chamber at high temperatures. This is because the outside lid surface is cooler than the inside surface. The expansion of the lid causes a slight gap between the lid and kiln body but not enough to affect the firing.
If the hinge does not allow the lid to float freely, the front of the lid can rise 1/4" - 1/2", causing heat loss. Placing a weight on the front of the lid can add stress to the firebricks. Instead, adjust the hinge so the lid has play that will allow it to float when the firebricks expand.