Lumis-LED enhances colour perception and contrast over SON-T for surveillance cameras
In response to the queries of various clients regarding the performance of the Lumis-LED when combined with camera surveillance, Innolumis carried out an A/B comparison between Lumis-LED Ecowhite and SON-T lighting in collaboration with Pelco Europe and Imtech Access & Security. The aim of this comparison was to test the usefulness of Innolumis LED lighting in areas equipped with surveillance cameras.
The situation
For the purpose of this comparative test, we visited the P40 personnel parking area at Schiphol Airport which is partly illuminated using conventional (SON-T) lighting (right-hand photograph), and partly by Innolumis’ type Lumis-LED Ecowhite lighting (left-hand photograph). The centre photograph shows the intermediate zone.
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Innolumis LED lighting |
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SON-T lighting |
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| source of photographs: feed from the Pelco test camera |
Test and background information
- The distribution of the number of lampposts over the area from right to left is identical.The SON-T 70W luminaires with a registered capacity of approximately 80W are on the right. The Lumis-LED 36W luminaires with a registered capacity of approximately 43W are on the left. The photopic measurement of light output in the area lit by Lumis-LEDs is lower than in the area lit by SON-T.The subjective visibility experienced by people who stood in both areas is comparable for both areas.
- A Pelco Spectra IV camera was used for the test and was linked to a standard TFT colour screen often used in control centres.
- The camera settings were not altered during filming, neither was colour correction applied subsequently.
- The photographs of the screen shown in this document were taken by digital camera, and were also not subsequently processed.
- The luminaires were tested under normal working conditions, and no changes were made to the power supply.
Conclusion:
The Ecowhite Lumis-LED provides excellent colour recognition and contrast. Good colour recognition is an essential feature for certain security applications. The following photographs show that in an area illuminated by Innolumis Ecowhite lighting, the camera’s colour definition is considerably better than with conventional (SON-T) lighting.
Innolumis LED lighting
SON-T lighting
Colour recognition is a problem with SON-T light sources, as the red tones look faded and green can hardly be recognised as a colour. Many dark colours also look grey and are difficult to distinguish. SON-T lighting has a negative effect on the applicability of surveillance cameras. Actually, white light is required to improve the performance of surveillance cameras. However, most of the light sources with good colour recognition are significantly less energy efficient than SON-T lighting, which creates a conflict between (social) safety and the quality of protection on the one hand, and energy consumption on the other.
The Lumis-LED Ecowhite emits a golden-green light resulting from green and red LEDs (also blue LEDs in the colour Moonlight). This combination of light colours is not only better suited to the light sensitivity of the human eye in situations where light is sparse, but also provides more colour information for the image sensor of a surveillance camera. This means that people and objects are easier to distinguish and that their colours are truer. This can be of crucial importance when circulating a description or describing a vehicle.
Tests have shown that in practice the use of Innolumis lighting results in better colour definition on the images taken by surveillance cameras.
How it works
As it becomes darker, the light sensitivity of the human eye shifts from yellow to green light. Traditional public lighting emits light that falls within the yellow spectrum and therefore does not profit from our greater light sensitivity in the dark. The result is that traditional luminaires need a relatively large amount of light to allow us to see properly. The Lumis-LED luminaires emit light in the colours to which our eyes are more sensitive at low light intensity (mesopic light level). Their golden-green light provides the correct light frequencies that activate the light-sensitive ‘rods’ and ‘cones’ in our eyes. This means that the Lumis-LED can provide the same visibility at a lower light level, thereby saving power.
Light sensitivity characteristics of a CCD sensor
Surveillance cameras
Surveillance cameras use an image sensor where each pixel is made up of sub-pixels for the red, blue and green light colours. The way surveillance cameras work is different to the human eye. Therefore the light sensitivity of the image sensor does not increase at very low light intensities, and the mesopic sight effect experienced by human beings does not occur. However, from the test carried out at P40, it is evident that cameras perform exceedingly well with the Lumis-LED as the light source. The colours are truer to nature than those reproduced under SON-T lighting, and the contrast and depth are also considered to be clearer under Lumis-LED lighting. This is because the light frequencies emitted by the Lumis-LED correspond much better with the light sensitivity characteristics of the image sensor: the green and red peaks in the distribution of light frequencies coincide with the sensitivity of the image sensor’s sub-pixels. The fact that scarcely any blue light is emitted evidently has little effect on colour recognition.