Catching vehicle license plates at night.

One question that we get on a fairly regular basis is “can a CleverLoop security camera system get usable footage of vehicle license plates at night?”.

The simple and honest answer is sort of, but not with any great reliability, but as with many things, the issue isn’t straightforward.

Image of the back of a car with the brake lights on. The number plate is clearly visible.

So why is getting footage of a license plate so difficult, and what can you do to maximise your chances of getting useful footage of vehicles that might enter your property?

First up, it is worth pointing out that this isn’t a problem with CleverLoop security cameras, as some of our customers have been told, it’s a problem with almost all night vision capable ip cameras or security cameras.

There are two things that make catching the details of license plates hard:

  • vehicle headlights over exposing the cameras, and;
  • infrared light reflecting off the license plate itself.

If it’s dark and your CleverLoop outdoor camera is running in infrared night vision mode, and a vehicle drives towards it, the headlights mean that the camera rapidly switches to day mode. The problem is that in a scene that is mostly dark, the intense light from the headlights will overexpose, or ‘dazzle’ the sensor in the camera, and you get no useable footage. You will however get an alert from that camera telling you it has seen something major – in this case the lights of a car.

This image is from a camera looking at a car with the headlights on high beam. The camera is at about waist height, and roughly 45 degrees on to the front of the car. The camera is in day time mode, and being dazzled by the headlights.

This image is from a camera looking at a car with the headlights on high beam. The camera is at about waist height, and roughly 45 degrees on to the front of the car. The camera is in day time mode, and being dazzled by the headlights.

There is less of an issue when viewing a vehicle from behind, particularly if it is just tail lights rather than brake lights, with both the lower intensity and the red colour dazzling the camera less. In some instances the red light can be enough to switch the camera to daytime mode, but not dazzle it, meaning you get nice clear images of the license plate, illuminated by it’s own light. In other cases, the red light isn’t enough to switch the camera out of night vision mode, but if the camera angle is right, the lack of direct reflection from the number plate means it is easily visible.

Rear of car, with tail lights on, viewed from close up and at 45 degrees to the number plate.

This image show the rear of a car with tail lights on, viewed from 45 degrees onto the back of the car, and from quite close up. Despite the camera still being in night vision mode, the angle means that the number plate reflection isn’t obscuring the details.

 

Image of the back of a car with the brake lights on. The number plate is clearly visible.

In this screenshot from a camera looking at the back of a car, the right hand lights are locally dazzling the camera, but also mean the camera has switched to day time mode, and the number plate is clearly visible, being illuminated by its own lights.

When trying to get footage of a vehicle that doesn’t have it’s lights on, the issue is that anything reflective on the vehicle will generally reflect infrared light even better than visible light. The end result is that all you see of a license plate being illuminated by infrared light is a shining bright silver patch on your footage.

Front on view of a car with no lights on. Camera is in night vision mode, and number plate is reflecting strongly.

This screenshot is from a camera pointing front on at a car that has no lights on. The infrared light from the camera in night vision mode is reflecting strongly from the number plate, making it completely unreadable.

 

Rear of car with tail lights on, camera still in IR mode and number plate reflecting strongly.

This image show the rear of a car with tail lights on, viewed from directly behind the car. The tail lights aren’t bright enough at this distance to switch the camera out of night vision mode, so the infrared light is reflecting strongly off the number plate, making it unreadable.

Given these issues, what can you do to catch better footage of vehicles at night, short of spending thousands of dollars on a specialised and dedicated license plate camera?

By far the biggest tool available to you is the placement of your outdoor security camera. You are going to see the best results from a location that allows the camera to catch the rear of a vehicle, from fairly low down (waist to chest height), and looking at a 45 degrees at the vehicle (rather than looking more directly at the side or back of the vehicle).

This is the front view of a car with normal headlight on, taken from about chest height, and from a roughly 45 degree angle to the number plate. The camera is in daytime mode due to the brightness of the headlights.

This image taken from a camera in a sweet spot looking at the front of a car, with the headlights on. In this case the headlights are bright enough for the camera to have switched out of night vision mode, and camera position is minimising the dazzling effect, allowing a grainy view of the number plate. This situation would be hard to replicate with a fixed outdoor camera.

The other thing to consider is that regardless of whether you catch the license plate of a vehicle, you are going to get the most useful detail from your security footage if the vehicle stops while it is view of a camera. Things like vehicle make, model and style are going to be a lot easier to pick out if you have got infrared footage of a car that is stationary. Think about putting cameras at gates or other obvious places where people are likely stop if they are driving into your property.

Finally, don’t forget to have other cameras situated to catch potential intruders after they have left their vehicles and are approaching your property, as well as indoor cameras set up to get footage of them as they move around inside. Collecting evidence from your your CleverLoop camera security system is like telling a story. The better and more detailed it is, the more likely law enforcement are to be able to identify the people involved and act on it.

by Cleverloop Team
December 22, 2016