Specifications

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KNOW-HOW: IR Floodlights

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S85

The use of infrared light (IR) in the video surveillance becomes more and more important. For

this purpose, external floodlights or floodlights which are integrated into a camera can be

used. With these floodlights it is now possible to achieve usable B/W recordings even in total

darkness.

Requirements made on the camera

IR floodlights can be used together with B/W cameras or colour cameras with day/night

switching. Sole colour cameras cannot be used, because they suppress the IR light with a sup-

pression filter. The IR suppression filter is used to prevent overexposure caused by the high rate

of infrared in the sunlight in case of strong solar radiation. With current day/night cameras,

this filter will mechanically be moved from the beam during the switching process.

The sensitivity of a camera is generally greatly reduced in the IR range. Compared with

standard sensors, cameras with a built-in EXVIEW image sensor feature a clearly higher sen-

sitivity in the IR range.

In order to ensure a higher reliability of the illumination, it is useful to plan with only half

of the max. operating range.

IR Floodlights

Different wavelengths

IR floodlights are offered with IR light of different wavelengths. In this connection, they are also

called discrete and semi-discrete floodlights. The infrared light is generally invisible to the

human eye. However, when the infrared light is created, there is always a little light visible in

the red area. It is such a small amount, it is only visible if we look directly into the floodlight.

These semi-discrete floodlights with a wavelength of 880 nm then merely glow red.

The longer the wavelength of the IR light, the greater the distance from the visible red light

and the weaker this effect becomes. With discrete floodlights with a wavelength of 940nm,

there is no light visible anymore. These floodlights are completely black, even in darkness.

The sensitivity of the cameras for IR light decreases with increasing wavelength. That is the

reason why the floodlights featuring a wavelength of 940nm, but otherwise of the same

design, seem to have a smaller operating range than the floodlights with 880nm. If total

invisibility is not required, floodlights with 880nm should be used.

Operating range and radiation angle of IR floodlights

The operating range depends on different factors. The most important

one is the reflection capability of the illuminated surfaces. In case no

light is reflected, the camera cannot display any visual contents.

In order to achieve a perfect result, the radiation angle of the IR flood-

light and the focal length of the lens must be matched to each other.

If a floodlight (wide radiation angle) is used together with a telelens

(large focal length), the picture may be too dark. Vice versa, a spotlight

(small radiation angle) causes a bright spot in the picture when used

with a wide angle lens (small focal lens).

10 20 30 40 50 60

880nm

IR-98/20

IR-12/65LED

IR-56LED

IR-98LED

IR-294/60

65∞/12m 60∞/18m 60∞/25m

METER

60∞/40m 20∞/60m

METER 103456789 11121314151617

940nm

IR-28PLATE

IRU-56/60

IRU-98/60

160∞/3.5m 60∞/13m 60∞/17m