Reading Tube Blemishes: Black Spots, Chicken Wire and Halo (2026)

How does the zone map work?

Manufacturers divide the circular image into three concentric zones. Zone 1 is the center - the small circle you actually look through most of the time. Zone 2 is the ring around it. Zone 3 is the outer periphery, the edge of the field of view. The map exists because a spot's location matters as much as its size: the same tiny mark is a dealbreaker in Zone 1 and completely irrelevant in Zone 3. When you read a blemish map, always check the zone first, then the size. This is one line on the larger test record, and the whole document is walked through in how to read a QC sheet.

What do the blemish terms actually mean?

The vocabulary sounds alarming and mostly is not. Black spots (also called dead spots) are dark points where the tube does not intensify - they matter by size and by zone, and only a sizable one in Zone 1 justifies rejecting a tube. Bright spots are the opposite: points that glow regardless of the scene. A bright spot in the center is a genuine defect and a reason to reject; a small one in the periphery is not. Chicken wire is a faint hexagonal pattern from the microchannel plate structure - it is rare in modern tubes and only relevant if it is visible in normal use. Edge distortion at the very rim of Zone 3 is normal optical behavior, not a flaw.

What is halo, and why does it vary?

Halo is the ring of glow you see around a bright light source - a distant porch light, a star, a vehicle far off. It happens as electrons scatter slightly at the tube's front stages, and smaller is better. Halo size is partly a generation and construction story: Gen 3 filmless tubes generally show less halo than older designs, because removing the ion barrier film reduces the scatter. It is not a defect you reject a tube over; it is a performance characteristic you compare between tubes. A tighter halo means bright points stay crisper and bleed less into the surrounding scene.

Which blemishes should actually change a purchase?

Keep the list short. Reject on a meaningful black spot or bright spot in Zone 1, because it sits in your sightline every time you use the unit. Be cautious about large or clustered spots in Zone 2. Treat small peripheral spots in Zone 3 as normal - they exist on tubes at every price and generation, including the most costly. The reason we can be this specific is that the map ships in the box; the policy behind that is in why we publish per-tube QC sheets, and the three-question email that filters sellers who will not show you a map is in spec sheets compared.

Frequently asked questions

Are black spots on a night vision tube a defect?

It depends on size and location. Small black spots in the outer periphery are normal at every generation and price and are not defects. A sizable black spot in Zone 1, the center of your field of view, is the one worth rejecting because it sits directly in your sightline.

What is chicken wire in a night vision tube?

Chicken wire is a faint hexagonal pattern that can come from the microchannel plate structure. It is rare in modern tubes and only matters if it is actually visible during normal use. A blemish map will note it if present, but most current tubes do not show it.

What causes halo around bright lights?

Halo is a ring of glow around bright points, caused by slight electron scatter inside the tube. Smaller halo is better. Gen 3 filmless tubes generally show less halo than older designs, but some halo is normal and it is a performance characteristic to compare, not a defect to reject.

Where is the blemish map on a QC sheet?

It is a small grid or diagram of the circular field, divided into zones, marking any cosmetic spots by location and size. Every Night Operators analog unit includes this map for the exact tube in the box, so you can see what is there and in which zone before you ever use it.