When considering which security camera to purchase, the minimum illumination level is often one of the most important specifications to keep an eye on. But unlike other important stats such as resolution or compression, minimum illumination cannot be represented by a hard and fast number. Here’s why.
The problems of measuring low-light security camera performance
Without light, there is no image, and without an image a security camera is useless. Minimum illumination - the lowest light level at which the camera can provide a usable image - determines what the camera is useful for. If you need night-time surveillance of an area, you’re going to need a security camera that can handle low luminance well. A camera’s light sensitivity is most commonly expressed in lux, which is the SI unit for illuminance. Below is a very rough guide to real-world lux levels:
| Lux | Conditions |
|---|---|
| 50,000 | Sunlight |
| 10,000 | Daylight |
| 1,000 | Overcast day |
| 500 | Indoor office |
| 100 | Dark day |
| 1 | Twilight |
| 0.1 | Full moon |
| 0.0001 | Overcast night |
We say ‘very rough guide’ because the real-world measurement of light sensitivity is not standardized across the industry. In other words, there is the opportunity for ‘legitimate’ fudging of figures for cameras that might perform poorly if subjected to variations on the same test. So, although two tests might be valid in terms of their fairness, the data gathered from these tests could vary significantly, making comparisons between manufacturers difficult.
The biggest discrepancy lies with how lux is measured. Lux measurements are taken with a lux meter. However, this measures the light levels in general, not in terms of how they will be picked up by a camera. So, for instance, a dark wood desk in an office will not reflect as much light as the white paper pad lying on it. Although the lux level might suggest that both of these objects would be picked up by the camera, in this real-world example the camera might not be able to pick out the desk as well as the pad.
This is not the only problem. It is very rare in real-world scenarios for light levels and light sources to be consistent across a camera’s field of view. These variations can prove challenging for cameras to cope with – something that would be hidden in the original lux measurements.
More things to think about
Alongside lux, there are a number of other factors that can alter a camera’s measured (as opposed to perceived) performance. Here are a few, with their pros and cons – as you will see, it soon becomes very difficult to adequately outline what a good low-light camera should look like on paper:
- Exposure: though low-light performance can be improved by increasing exposure times, this will lead to motion blur in any captured or observed video feed;
- F-number: a lower f-number generally means better low-light performance, but again, these figures can be manipulated to make it appear that the camera performs better than it actually does;
- Lens: low-light performance is dependent on choosing the correct lens for the correct sensor. A cheap or poorly chosen lens will hinder a camera’s ability to perform well in low light;
- Sensor: time was when you could rely on the size of a camera’s sensor to determine how well it was going to cope with difficult conditions. Now, with advances in technology, certain designs can achieve excellent low-light performance at small sensor sizes.
What's the solution?
There is only one way to be sure you are picking a camera that will fulfil the requirements of your installation – testing. However, this is not always possible. If it’s not, you have a few options available to you:
- Go for authority: find a review of your chosen camera and read it. Ensure that the source of your review is authoritative – we provide some product evaluations of our own on our blog.
- Pick your manufacturer: try to go off the other features you need first and pick your manufacturer from that. If the manufacturer has any credibility at all, it should be using a consistent benchmark test to measure minimum illumination for all its cameras, so at least this way you know the comparative scores are as accurate as possible.
- Go thermal: if you really need your security camera to be monitoring in darkness all the time, and you value detection over identification, thermal technology might be the way to go. It is more expensive and less feature-rich than conventional visible light cameras, but as a reliable detection method in extremely poor lighting conditions it is unbeatable. Check out the Axis Q1941-E as an example;
- Ask for advice: give our customer services team a call and they can assist you with any queries you may have.
Ultimately, specifications can only be a guideline for choosing a camera. There can be any number of real-world issues that affect the performance of security cameras which will only reveal themselves upon installation. Minimum illumination is among the trickiest of these to judge, but if you take the above steps you should end up with a solution that goes a long way to fulfilling your requirements.