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.
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