Introduction

 

The new Derwent Night time Guide is designed to pull together Derwent`s full product range, demonstrating that the range offers the solution for any infra-red requirement short range or long range, internal or external. Also for the first time Derwent have combined our experience in illumination with camera technology to develop combined camera and LED solutions.

         

Derwent`s product range has grow to ensure we well placed to support installers and the industry as whole in designing and implementing leading night time CCTV schemes

        

        

What is Infra-Red?

     

Infra-red for CCTV purposes is the light that the human eye can not see but the camera can, sometimes called black light. Derwent are regarded as technical leaders in taking advantage of this for use in night time CCTV applications. The diagram below demonstrates what the human eye can see (photopic curve approx. 400-700nM) and what a normal monochrome camera can see. Diagram b, demonstrates the increased sensitivity of more specialised IR sensitive monochrome cameras.

     

       

         

Graph A                             Graph B

 

Camera Sensitivity

          

It is important to notice that the camera sensitivity drops as the wavelength increases. This means that the camera can see less of the light distributed on the scene.

     

Infra-Red Filter options

         

However there is often a requirement for semi-covert or covert installations. Diagrams C, D and E demonstrate a 730nm filter, 830nM and 950nM filter. Generally speaking the 730nm filter will glow similar to a traffic light, an 830nM filter will give off a dull red glow only just visible to the human eye. The 950nm will appear totally covert, no glow is visible.

 

   

Graph C             Graph D             Graph E

The key factors in choosing the type of IR lamp often relate to the required viewing distance. As demonstrated in the diagrams above the sensitivity of the camera is an important element, additionally the lens type and sensitivity play an important role.      

          

The chart below indicates what distances you can expect to achieve in relation to you’re chosen camera (for specific information please contact us directly).

         

 

LED

30/850

Single flood

Single 30º

Twin

30º

Single 10º

Twin

10º

Single Spot

High performance camera/ lens

60

70

(45)

100

(70)

140

(100)

140

(100)

200

(145)

170

(130)

Medium performance camera/ lens

45

55

(35)

75

(60)

105

(80)

105

(80)

150

(115)

130

(100)

Low performance camera/ lens

30

35

(25)

50

(40)

70

(55)

70

(55)

100

(75)

85

(65)

 

The above ranges are indicated as a quick guide and the actual results depend on the performance of the camera and lenses as well as the reflectivity of the scene, weather conditions, etc.

        

The diagram below represents Derwent`s lens options available on the Uniflood 500 & Uniflood 300.

 

 

        

  Spot                      10º Cosec           30º Cosec                 Flood    

 

       

As a manufacturer we designed Uniflood and Miniflood to combat four key factors:

even Illumination

long bulb life

Lower power consumption

Lower Cost of ownership

Beam Patterns

 

         

Uniflood Range                                     Miniflood Range

 

Derwent Uniflood Spot and Flood beam are designed for targets as described in the following graphs. The spot and Flood are not intended to be used together as is normally the case with traditional IR.

 

The 10º and 30º Cosec beams are designed for even illumination to replace the traditional Spot / Flood combination.

 

High spec schemes for long distance open scenes often use a live Zoom lens – say 16-160 specify 10º + 10º cosec lamps. For a shorter zoom, say 10 –100 a 10º + 30º is a good twin lamp set up, that will give even illumination avoiding white-out and black areas on the viewing screen.

       

Solid State IR illumination

            

The LED units can provide up to 10 years life. However they generally provide less power on scene then halogen IR lamps. LED’s are beginning to make a bigger impact on the CCTV scene because of the increased IR sensitivity of emerging monochrome cameras.

          

Solid state devices such as LED (Light Emitting Diode) bring major advantages, such as lower maintain maintenance levels and lower power consumption.

       

Finally

        

The final message is to remember you are proving illumination for CCTV schemes and not for pedestrian schemes, remember to match the illumination with the scene and lens focal lengths, choose your camera wisely and use our experience to help you achieve the desired picture quality.

      

     

Spot Beam Application

         

        

       

Flood Beam Application

     

       

  Local Short Range illumination

 

    

 

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