In short: Almost every tube has some minor “cosmetic” imperfections – black spots, a faint honeycomb pattern or small bright spots. Manufacturers treat them as acceptable as long as they don’t interfere with viewing. Operational defects are different – shading, edge glow that stays when the lens is covered, or flickering – and are grounds for a warranty claim or service. You’ll spot them best in a dark room, with the lens cap on, and against an evenly lit surface.
Cosmetic vs. operational defects
Manufacturers and aviation authorities sort image faults into two groups. We use the terminology of ATN’s official PVS-14 manual and a bulletin from Australia’s Civil Aviation Safety Authority (CASA) – sources below:
- Operational defects – according to the ATN manual, an immediate reason to stop using the device and send it for service: shading, edge glow, flashing or flickering, and intermittent operation. CASA also lists them as unacceptable.
- Cosmetic blemishes – according to ATN, usually the result of manufacturing imperfections and not a reason for rejection unless severe enough to interfere with use. ATN also notes that some types can get worse over time.
| Defect | What it looks like | How to check | Classification per ATN / CASA |
|---|---|---|---|
| Black spots (blemishes) | small dark dots in the image | look at an evenly lit surface | cosmetic; acceptable if it doesn’t interfere with viewing |
| Bright spots | small bright area, may flicker or stay constant | cover the lens – usually disappears | cosmetic; acceptable if it doesn’t interfere |
| Emission points | sharp pinpoint of light in a fixed position | cover the lens – does not disappear | cosmetic; not every one is grounds for rejection |
| Chicken wire | irregular pattern of thin dark lines | look in higher light | cosmetic if it doesn’t interfere |
| Honeycomb (fixed pattern noise) | faint hexagonal pattern across the image | at high light levels | cosmetic if it doesn’t interfere |
| Edge glow | bright (sometimes sparkling) area at the edge of the image | cover the lens – if it stays, it’s a defect | operational – service |
| Shading | image is not fully circular, part of it is dark | also check your eye relief | operational – service |
| Flicker, intermittent operation | image flickers or drops out | replace the battery, check contacts | operational – service |
Blemishes – black spots
Black spots are the most common cosmetic blemish. According to the ATN glossary, they can be a cosmetic blemish in the tube itself – or dirt or debris between the lenses. The difference matters: dust in the optics can be cleaned by a service centre, a spot in the tube stays.
ATN and CASA both treat black spots as acceptable as long as they don’t interfere with viewing. So size, number and especially position matter – a spot in the centre of the field of view is more distracting than the same spot near the edge. Specific tolerances (how many spots of what size) vary by tube manufacturer and are not universal, so we don’t quote any here.
Bright spots and emission points
Both look like a bright dot in the image, but they behave differently when you cover the lens:
- Bright spot – a small, non-uniform bright area that may flicker. According to ATN, it usually goes away when all light is blocked.
- Emission point – a sharp, steady or fluctuating pinpoint of light in a fixed position that does not go away even when the lens is fully covered.
Before you go looking for a defect, make sure it isn’t a real light source in the scene (a distant street lamp, for example). According to ATN, not every emission point makes a device rejectable – what matters is whether it interferes with use.
Chicken wire and honeycomb
Chicken wire, per ATN, is an irregular pattern of thin dark lines in the field of view – across the whole image or in parts of it; in the worst case the lines form hexagonal or square-wave shapes. CASA attributes it to fibres that don’t transmit light at the boundaries of the fibre-optic bundles. It is typically visible in higher light.
Honeycomb (fixed pattern noise, FPN) is a faint hexagonal pattern across the image. According to ATN it shows up at high light levels or when looking at very bright lights, and can appear in any tube if there is enough light. Both are cosmetic as long as they don’t interfere with viewing.
Edge glow and shading
Edge glow is a bright, sometimes sparkling area at the outer edge of the field of view. To check, cover the objective lens with your hand or the cap: if the bright area stays, ATN treats it as an operational defect and the device needs service. CASA states that edge glow brighter than the background scintillation is grounds for rejection.
Shading means the image isn’t fully circular – part of the field of view is dark. First make sure your eye is at the right distance from the eyepiece; if the shading persists, it’s an operational defect.
A faint sparkle in the image in very low light (scintillation) is normal according to the ATN manual and is not a defect.
Burn-in
CASA also lists uneven image brightness (image disparity), which can result from prolonged exposure to bright light – the image gets “burned into” the tube. So don’t leave night vision switched on facing bright light, and store it with the lens cap on.
How to check for defects – step by step
- Check the device in the dark. Give your eyes a few minutes to adjust and focus the eyepiece.
- Put the lens cap on or cover the objective with your hand. Look for bright areas at the edge (edge glow) and points that don’t go away (emission points).
- Look at an evenly lit, featureless surface (e.g. a wall in dim light). This is where black spots, chicken wire and shading show up best.
- If you see a black spot, try refocusing both the objective and the eyepiece: if its sharpness changes with the optics, it may be dirt rather than a tube defect.
- In higher light (e.g. with a lamp on in the room, not pointing straight at it), check for honeycomb and chicken wire.
- Watch for flickering. If you see any, replace the battery and check the contacts first.
- Photograph any defects through the eyepiece and compare them with the datasheet and the seller’s description when buying or making a claim.
What is normal and what isn’t
- Normal: a few small black spots away from the centre, faint chicken wire or honeycomb in higher light, scintillation in very low light.
- Worth considering: prominent spots in the centre of the image, an emission point that distracts you, or defects that get worse over time.
- Reason for service or a claim: shading, edge glow that stays when covered, flickering or the image dropping out.
When buying a used device, ask for photos of the image and the original datasheet with the serial number – see Buying used night vision: risks and a checklist and How to read a tube datasheet.
Sources
- ATN Corp.: PVS-14 Operator’s Manual, section 2.2.3 “Inspection Criteria for Proper Image Intensifier Operation” and glossary – Official manufacturer manual (external link, third party – NGS is not responsible for its content) (checked 9 Nov 2026)
- Civil Aviation Safety Authority (Australia): Airworthiness Bulletin AWB 25-031 “Defects with Night Vision Imaging Systems”, Issue 8, 3 Sep 2021 – casa.gov.au (checked 9 Nov 2026)