CCTV Installation lighting

CCTV Intallation: Understanding the light spectrum

Rainbows show all colours humans can see. Violet/blue are short wavelengths of around 400nm (nanometres: billionths of a metre) progressing across the rainbow spectrum to red at around 700nm.We are most sensitive to green light; less so to blue and red. The standard graph of this is the ‘photopic curve’.This is built into light meters (measuring ‘lux’) so figures are meaningful when we’re designing environments for human eyes.For instance, sunny days may be 30,000lx, dropping to 500lx in an office, and only 5lx street lighting.Incidentally, because IR is beyond human visibility your lux meter is, by definition, completely insensitive to it. Be aware that sellers of “zero lux” CCTV might deliver nothing more than a camera which is simply IR-sensitive, like many others, not the best option for a CCTV installation.Cameras’ sensors respond to a wider range of wavelength than our eyes. Much sensitivity is in the infrared region.However, for realistic colour video this IR needs to be suppressed so an IR-cut filter is put over the chip.Consequently, colour cameras and IR lamps are not designed for use together. Nonetheless, when a ‘day/night camera’ switches to monochrome it physically shifts this IR filter so natural IR sensitivity is fully utilised at night.

CCTV installation requires that consideration is given to the lighting, other wise it can render the CCTV installation useless

So why is poor lighting so commonplace in CCTV installation and CCTV systems?CCTV pictures all begin when light or infrared (IR) hits the camera’s sensor. IR is the same as light but its longer wavelength is outside our eyes’ range so we call it invisible. Cameras, however, generally can see both. Let’s begin with the eye-friendly visible stuff.

Ensure that your CCTV installation takes image clarity into account.

For best image clarity our lighting should enable the camera to maximise contrast. Black should appear…well…black. White should be as bright as possible. That means plenty of light on the scene, but how much is plenty?

Night time surveillance lamps, an important aspect of your CCTV installation

At night the colour’s we perceive can be greatly influenced by colour’s emitted by our light source. Compared with perfect daylight, tungsten/halogen lamps give excellent ‘colour rendition’ but running costs can be high.‘White light’ approximations from metal halide, fluorescent and LED lamps are good and more energy efficient.‘Orange white’ from high-pressure sodium lamps is commonplace but colour rendition is worse.Cameras tend to have AWB (auto white balance) active but this doesn’t correct poor colour rendition.Low-pressure sodium lamps are very efficient and commonplace but emit only one colour, yellow, so distinguishing colours is impossible.The same is true of infra-red light which is used with cameras in monochrome mode. Beware, a target reported wearing dark jacket and light trousers under IR light might under visible light appear the opposite – light jacket and dark trousers – because materials reflect wavelengths differently.Wavelengths focus differently, too. IR-corrected lenses are designed to minimise any out-of-focus effects when switching from visible daytime to IR night time illumination. Especially when using non-corrected lenses make sure focus is adjusted with iris fully open (minimum depth of focus) under IR light.When under daylight the iris shrinks and the increased DoF should reduce effects of focus shift.‘Non-covert’ tungsten-based IR lamps (deep red glow around 750nm) need less correction than ‘semi-covert’ lamps (dim orange glow around 830nm) and, again, less than ‘covert’ lamps (nearly invisible glow of 950nm).Cameras’ sensitivity to IR drops as wavelengths increase so more IR light is needed (in watts/m2 rather than lux) to produce your image.Field trials are strongly recommended for your cctv installation, rather than relying on a manufacturer’s vague estimates surrounding IR performance.

LED lighting Considerations for your CCTV installation

LEDs will, doubtless, continue to advance the world of CCTV lighting, both visible and infrared. For instance, flood lamps are improving in output, and some dome cameras now carry lights rather than rely on separately mounted arrays of static lamps.Lighting design has for a long time been a dark art, literally and figuratively.Often CCTV lighting isn’t so much badly designed as not designed at all, relying on what is already in place. I hope a light bulb has just come on above your head signalling some new ideas and important considerations for your CCTV installation.