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IR LED Range & Count for reliable Night Vision

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dineshkumar@hw

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Hi,

Currently I am working on a surveillance camera module. Consider that my application scenario is to use in a bus (Length 12 to 40 feet and width 8 feet maximum).

When I came across the design, I am confused with the following.

1) How to identify the maximum distance over which the IR LED emits the light?

2) How many IR LED's will provide a clear night vision?
I found 24 , 36, 48 and so on in market products.

3) The angle of radiation plays any role in the count of LED's used?
 

You will want the LED angle to be far less than the camera viewing angle, and more like the narrow field of view at 40 ft.
Objects far from centre will be much closer and Lux or lumen levels will increase by 4x as distance is dropped in 1/2

Historically 5mm IR LED view angle is defined as +/- half angle at 50% output while visible LED's use the full angle, 2θ1/2 for specs. Thus something in the 10 deg. range centred down the aisle would seem about right.

You will have to lookup the maximum safe level for eyesight.

**broken link removed**
Inverse Square Law also depends on angle.
 
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Hi,

2) How many IR LED's will provide a clear night vision?
Click to expand...

it is not a question of the count of IR-LEDs. It is the intensity, the brightness of the LEDS, the spectral sensitivity of the sensor, the IR LED spectrum, distance to the object, needed intensity/brightness of the objects.

So it is impossible to give an answer.

Klaus
 


You had not informed exactly what is the purpose of the system, whether is needed a bare detection of movement, if need to just store sampled pictures of the hall for further analysis on demand, or if need to perform image recognition and classification for counting of incoming passengers through the door, for instance. In shorts, it is your design specification what will dictate the required performance of the illuminator & camera as a whole.
 

I agree Andre, luminance level, affects aperture size, focal range, SNR , acuity for facial recognition.

Just as flash photos give extremely poor depth of quality imaging, so a single source IR flood LED near camera will give poor depth of field. ( i.e. saturated near imaging and dark distant due to inverse square law yet linear light sensing, whereas our eyes have a wider logarithmic range.

The concept is poorly defined and thus poor results can be expected.

I would prefer distributed lighting.
 
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