Dark evenings: is your CCTV's night vision up to it?

Most CCTV cameras use infrared. A ring of small LEDs around the lens lights up the scene with light our eyes can't see, and the camera switches to black and white. It works in total darkness, which is why it's so common, but it has limits. You lose all colour, so a red car and a blue car look the same, and the range is set by the LEDs. Beyond that, the picture fades to black.

Colour night vision cameras use a more sensitive sensor and a wider lens opening to keep a colour picture in low light. They need some light to work with, such as a street light, a porch light or a small white light built into the camera. Where there's enough light, the footage is far more useful: you can see the colour of a coat or a car, not just its shape.

Some cameras do both, staying in infrared until they detect a person and then switching on a white light to record in colour. That also tells whoever is on the drive that they've been seen. If you choose a camera with its own light, it needs aiming so it lights your property and not your neighbour's windows. Our guide to home CCTV and the law covers where cameras can look.

When a camera that used to work well at night starts giving a poor picture, the cause is usually one of these:

• Spider webs. The infrared light attracts insects in the evening, and spiders follow. A web across the lens glows white at night, blurs the picture and sets off motion alerts every time it moves in the wind. Autumn is the worst time of year for it.
• Dirty or scratched domes. Dome cameras sit behind a clear cover. When it's dusty, misted or scratched, the camera's own infrared reflects off the inside and the whole picture turns to haze.
• Something too close to the view. A soffit, gutter, wall or hanging basket at the edge of the picture bounces infrared straight back. The camera then darkens the whole image to cope, and everything further away disappears.
• Failed infrared LEDs. They wear out, and on older cameras they often fail one at a time. If the night picture has slowly got darker, or a camera that used to show a faint red glow after dark no longer does, this may be why.
• A tired power supply. Infrared LEDs draw extra power. A failing power supply can cope during the day, then cause a flickering picture or a camera that keeps restarting once the LEDs switch on.

Cleaning a dome or brushing away a web is fine if the camera is in easy reach from the ground. Please don't climb a ladder to a camera under the eaves on a dark evening. We'd rather come out and do it safely.

Plenty of night vision problems are fixed without new cameras. Cleaning or replacing a dome cover, moving a camera a little to clear a soffit, replacing a power supply and adjusting the recorder's night settings can transform the footage. We repair systems of any make, including ones fitted by installers who are no longer around.

Upgrading starts to make sense when cameras are old analogue models with low resolution, when the infrared LEDs are failing on several cameras at once, or when you need to identify people rather than just see that someone was there. Modern 4K cameras pick out far more detail at night, and older systems can often be upgraded in stages using the cable that's already in place. If you're adding cameras at the same time, our guide on how many CCTV cameras you need will help you plan.

Whatever we fit or fix, we check every camera after dark as well as in daylight before we hand it over, because that's when it matters most.