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Determining IR Illuminator requirements

  1. Datasheets for security cameras typically list a mimimum illumination lux value, but typically don't mention the shutter speed needed for that lux value, which could be as long as one or two seconds.

  1. Datasheets for IR Illuminators typically list a coverage angle and distance, but typically don't mention a lux value at that maximum distance.

Suppose you want to set the camera's maximum exposure time to 1/25 to minimize motion blur and you want sufficient IR Illumination to 40 feet. I'm guessing you have to select an IR illuminator more or less based on experience because neither the camera nor illuminator datasheets provide sufficient information to calculate the illuminator power requirements. Am I missing something?

Best, Christopher

Reply to
Christopher Glaeser
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I've contacted manufacturers, distributors, and installers, and no one seems to have an anwer for this. In photography, it is possible to precisely determine the lighting requirements based on shutter speed, F stop, film speed, distance, and guide number. In security cameras, manufactureres toss around lux values without even specifying the shutter speed used to measure that lux value.

Best, Christopher

Reply to
Christopher Glaeser

That's because a video camera does not use shutter speed. The IRIS (aperture) control the amount of light hitting the CCD, and the captures on the CCD happens every 1/30 seconds. In video standard , you cannot force a longer exposure to capture more light.

LUX is almost equivalent to the ISO in film, and that 's the only thing you can go by in video camera as far as sensitivity to light is concerned.

Reply to
A.J.

I probably should have focused the discussion on the camera I actually own, which is an Axis IP camera, not a conventional analog CCTV camera. It's true that cameras like the Axis 223M don't have a physical shutter like many still cameras, but the "shutter speed" (or if you prefer, the "exposure time") can be controlled electronically, which is separate from the auto iris. When Axis mentions a lux value in their product specifications, they do not mention the exposure time (shutter speed) required. In addition, if you call tech support at Axis, they don't know the exposure time either. A low lux rating of 0.005 is of little value if the exposure time is 2 seconds (the maximum exposure time on the 223M) unless you want to film parked cars and measure tree growth. The 223M boasts a two megapixel sensor, but what value are all those megapixels if someone walking very very very slowly is still just a blur.

More important, this motion blur can be fixed. All I need is sufficient light. With sufficient IR illumination, I should be able to set the minimum exposure time to 1/25 or possibly 1/60 and get excellent, person-identifiable images. Right now, I can't tell if that's the postman or the dog. If the cost was $50, I'd place an order and try it, but a quality IR illuminator can cost $500 to $1000 and more. How much power do I need to light a driveway to 40 feet so I can use an exposure time of 1/25? No one seems to know.

Best, Christopher

Reply to
Christopher Glaeser

AFAIK, IR illuminator has nothing to do with the lux value of any camera. So, if you buy a IR Illiminator that is rated for 40', your camera will see

40', as long as it is IR capable.

Reply to
A.J.

My camera can already see to 40' at night due to a nearby street light. The problem is, I have to put a sign in my front yard explaining to would-be theives to please stand still for two seconds because the camera has a very long exposure time.

Best, Christopher

Reply to
Christopher Glaeser

On Jan 14, 6:16=EF=BF=BDpm, "Christopher Glaeser" wrote= :

If you live in a nice neighborhood, the theives will probably be a little more cooperative.

By the way, (And I know this is rather crude but) in all the CCTV systems I've installed, my rule of thumb is, if you want to see 40 feet at night with IR, get a camera with 80 foot IR illumiation capability. I've never had a problem seeing what was necessary.

Reply to
Jim

There are some things in *my* neighbourhood you *don't* want to see... ;-)

Reply to
Frank Olson

I think that rule of thumb is somewhat reliable for analog CCTV. I've not really looked at the specs of many analog cameras, but I suspect most use 25 to 30 frames per second. IP cameras are a bit different in that the frame rate is not constrained by NTCS or PAL frame rates, and can be considerably lower than 30 frames per second. Since the frame rate can be much less, the exposure time can be quite long. For this reason, IP camera manufacturers can take great liberties when reporting minimum lux values. Since they don't report the exposure time for the minimum lux value, there's a good chance they used something like 1/2 second, which would be very misleading.

Raytec recently announced the low-voltage RayMAX 50 Fusion IR Illuminator. The Fusion 50 with 50 degree coverage is rated at 92'. Unless I can find specific information that the Fusion 25 is more than adequate for my application, I'll probably get the Fusion 50 just to have the headroom.

Best, Christopher

Reply to
Christopher Glaeser

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