Does anyone have experience with 740nm IR illumination with Dahua cameras?

[wtimothyholman]

I've been using Dahua -Z12E cameras for LPR for a few years, but I've run into a situation where I may need to switch to 740nm IR illumination for nighttime imaging of the new license plates in my area (which have poor contrast at 850nm).

Has anyone else tried this? Do Dahua varifocal cameras perform acceptably well with 740nm IR sources?

I intend to buy an illuminator to experiment with, but I wanted to be sure there was no show-stopper at the outset.

 

[handinpalm]

You just need to look at a typical Quantum Efficiency (QE) curve for various Sony sensors that are used in a lot of Dahua cameras. The higher the QE for the particular wavelength, the more sensitive the sensor is at that wavelength. ie brighter. So at 740nm, you would have a brighter illumination, than at 850nm emitters or even worse at 940nm emitters where the QE drops off significantly. Go for the 740nm emitter, if you can find them, but they will not be as covert as the 850nm emitter since the band skirt will probably fall into the visible spectrum. If you put out too many 740nm emitters, you may find some unwelcome guests (red light district).

Quantum efficiency (QE) is the measure of the effectiveness of an imaging device to convert incident photons into electrons. For example, if a sensor had a QE of 100% and was exposed to 100 photons, it would produce 100 electrons of signal.

 

[wtimothyholman]

You just need to look at a typical Quantum Efficiency (QE) curve for various Sony sensors that are used in a lot of Dahua cameras. The higher the QE for the particular wavelength, the more sensitive the sensor is at that wavelength. ie brighter. So at 740nm, you would have a brighter illumination, than at 850nm emitters or even worse at 940nm emitters where the QE drops off significantly. Go for the 740nm emitter, if you can find them, but they will not be as covert as the 850nm emitter since the band skirt will probably fall into the visible spectrum. If you put out too many 740nm emitters, you may find some unwelcome guests (red light district).

Quantum efficiency (QE) is the measure of the effectiveness of an imaging device to convert incident photons into electrons. For example, if a sensor had a QE of 100% and was exposed to 100 photons, it would produce 100 electrons of signal.

Thanks very much for that chart. Given that the sensors are used with 850nm diodes, I hoped that there would be a monotonic response between visible light and 850 nm, and that seems to be the case. So the camera should be usable with 740nm illumination. Now to do some tests.

 

[samplenhold]

From that graph it appears that any of those sensors will be about twice as sensitive at 740 than 850.