A item you hold that tells you if you are within a torch radius. Basically the item would be one color and when you step out of the area it changes color.
Nothing fancy code wise, you only have to initially know if a torch is within a chunk before then checking the torches to see if one is within range.

running val3 1.16.5 at the moment but this would be really cool in future versions. I was using the torches and dread lamp combo to isolate a area in the nether to help improve spawn rates in the small area. I need to make a second issue though as it seem striders seem to ignore the torches/dread lamps, going to test that one in a minute before making a issue though.

There are several requests to determine the range of a torch. I'll investigate this a bit further.

Regarding your strider issue: Striders are (atleast in my 1.18 environment) assigned to the Dread Lamp be default. If moyang didn't change their classification, this should be the case for 1.16 as well.

Maybe an (equippable) item to show the range of a torch as a visual in the world. That would probably the most practical and very useful. As of right now it's very hard to place mega torches optimally.

My actual problem is the visualisation itself. It breaks in a lot of settings, especially when the torch range is bigger than the default 64 blocks. I've been experimenting with this on and off but it's not as trivial as other blocks showing a 3x3 box.

I don't really like the idea of using an item to indicate if you are in range, I want it to be a hologram in the world - everything else isn't exactly user-friendly