Night Surveillance - White Light Illuminator Testby Antony Look, posted on Jul 18, 2011
Getting quality surveillance images at night can be quite a challenge. A number of techniques, with widely varying price points and tradeoffs, are possible. In this report, we share our test findings on the newest emerging trend in night time surveillance - adding white light LED illuminators.
Almost all surveillance cameras have natural performance limits when it gets really dark out. Even the 'best' cameras will struggle needing to pump up the gain while overall image details rendered diminish. One common option with megapixel cameras is slowing the shutter but this increases the risk of creating ghost like images of moving objects.
Since there is only so much that can be done with conventional surveillance cameras, three common steps are generally employed to improve night time performance:
- Add street lighting: This can work very well but also requires an expensive construction project. This is easy to do with new construction but generally hard otherwise.
- Use thermal imagers: Thermal cameras do not need visible light at all and can 'see' objects far away. The downside is the cameras are expensive ($3,000 to $30,000) and provide minimal details. As such, these tend to be primarily used in critical infrastructure projects.
- Use IR illuminators: This is, by far, the most common step to improve night time surveillance. IR light, visible to many security cameras but not the human eye, can be used to provide significantly improved night time image. The main downside is that it does not work for color cameras or color capture mode.
Using white light LEDs illuminators is a fourth way to improve night time image quality. Like street lighting, white light LED illuminators add visible light. However, white light LED illuminators are much smaller than street lamps and can easily be installed adjacent to security cameras. Here's what the illuminators look like relative to the size of a hand:
These illuminators can be used to provide spot illumination on specific areas where surveillance is desired. They allow for color imaging and add the natural deterrent of visible light.
In this test, we tested both a mid and long range IR illuminator:
- Mid Range Illuminator - Rated for 85 feet and 60 degrees beamwidth; Model used - Iluminar WL220-60-24
- Long Range Illuminator - Rated for 162 feet and 30 degrees beamwidth; Model used - Bosch SLED30-WBD
We setup the two illuminators in a dark open field, and took lux readings at various distances and locations, comparing the light levels with just ambient light (i.e. dark, under 1 lux) and with the illuminators on. The results were documented in 2 visual maps (one for each illuminator). Below is a preview of the approach:
We then recorded video in b/w mode and color mode with the illuminator off and then with the illuminator on, as a subject moved from the far field to the near field. The illuminator off image served as a reference to compare the practical benefits of deploying visible white-light illumanators in a real-world surveillance application. Here is a sample preview:
Finally, we compared three (3) day/night cameras throughout a series of tests featuring both long- and mid-range illuminators, b/w mode and color mode settings, and wide, moderate and narrow FoVs). Here is an unmarked preview:
This approach allowed us to quantitatively and systematically understand the potential benefits and tradeoffs of using white light LEDs. Inside we answer questions including:
- How significant of an impact did the white light LEDs have on camera performance?
- How much light did the white light LEDs add at different areas within the scene?
- What, if any, decreases in bandwidth consumption did the LEDs deliver?
- Which, of any, of the 3 cameras performed the best? In what conditions?
- Should you even consider using white light LEDs?
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