Infrared light from the built-in illuminators is reflecting off the inside of the bubble back into the lens - almost always because the light gasket is not seated.

A foam or rubber ring around the lens seals it against the bubble so the illuminator output cannot reach the lens directly.

The gasket is easily displaced when the camera is aimed, which is why the fault appears after installation or after a service visit.

Fingerprints, dust and scratches on the bubble make it worse by scattering the light.

Check by covering the bubble's inner surface near the lens: if the image clears, the gasket is the problem.

Where the effect cannot be eliminated, external illuminators mounted away from the camera remove it entirely.

Yes - a tinted bubble absorbs light, and the loss shows at night rather than in daylight.

The tint is there to conceal which way the camera is pointing, which is a genuine deterrent and an operational advantage.

It also reduces the light reaching the sensor, and in a low-light scene that decides whether the image is usable or merely noisy.

Where identification at night matters, a clear bubble is the better choice and the concealment is given up.

Some installations use tinted bubbles in well-lit public areas and clear ones in dark external positions, which is a reasonable compromise.

Test with the actual bubble before committing across a site. The difference is easier to see than to calculate.

An impact rating for the housing and bubble, plus fixings that cannot simply be unscrewed - and it is a different rating from weatherproofing.

Impact resistance is stated as a rating covering the energy the housing will survive.

Metal bodies with polycarbonate bubbles are the standard construction, because polycarbonate absorbs impact where acrylic cracks.

Security fixings requiring a specific tool prevent the camera being removed, which is the simplest attack of all.

Ingress protection is separate and covers dust and water, so an external dome needs both ratings.

Mounting height is still the most effective protection. A camera out of reach does not need to survive an impact.

Indoors, in public-facing areas, and anywhere the camera should not dominate the space or advertise its direction.

Retail, hospitality, offices, schools and transport interiors are the standard applications.

The low profile suits suspended ceilings and does not intrude on an interior design.

Concealed direction means a person cannot easily work out where the camera is not looking.

For long external views a bullet camera usually performs better, because it takes a larger lens and a sun shield.

Where deterrence depends on the camera being obviously present and obviously aimed, a bullet is more visible - which is sometimes the point.

With a soft cloth and a mild cleaner, never anything abrasive - and the bubble should be treated as a replaceable part.

Scratches scatter light and soften the image permanently, and abrasive cleaning is the usual cause.

Ultraviolet exposure yellows polycarbonate over years, which shifts colour and reduces light transmission.

Replacement bubbles are available for most models and cost far less than a camera.

Include the light gasket check whenever the bubble is removed or the camera is re-aimed.

Schedule cleaning by environment: a kitchen or a workshop dome needs it far more often than an office one, and image quality degrades gradually enough that nobody notices until footage is needed.