SHOWALL FUN PRANKS HIGH VOLTAGE LAZARUS-64 PHOTOGRAPHY SPY GADGETS VIDEO GAME
Figure 16 - This is the test rig that will be used to compare the LED outputs
Figure 16 - This is the test rig that will be used to compare the LED outputs

Most camcorders have a video input connector to allow recording from another video source. This input may be labeled VCR Input, or External Video, and will basically replace the input from the camcorder's built in video system with your external source. This is necessary because all camcorders actually block infrared light to improve the quality of the visible color image. There is no easy way to remove the infrared filter in a camcorder, so unless you are willing to go in deep with your tools, you will need an infrared friendly video source. In my case, it is the low lux monochrome spy camera, which has been stuck to the side of the camera with a bit of double sided tape.

The LED array would normally fit over the camera lens, but I just taped it to the front of the camcorder as shown in Figure 16 that so I could switch back and forth from the spy camera to the original lens on the camcorder. Both the external camera and LED pulse circuit are driven from a 12 volt battery pack.



Figure 17 - These images were captured from the camcorder recordings
Figure 17 - These images were captured from the camcorder recordings

The final results show that the pulsed mode operation of the LEDs does in fact offer a stronger illumination than the same LEDs running under direct current. In Figure 17, (A) shows the image as seen by the camera under full room lighting. Image (B) shows the same scene using the LED array in continuous current mode, running all 10 LEDs in series from a 12 volt power source. Image (C) shows the LED array running from the pulsing circuit using the high current transistor. And finally, Image (D) shows the room as seen by the camera with only the ambient light coming into the window from the streetlight across the street.

The tests clearly show that the pulsed mode operation of the 10 LED array offers the most illumination in the interior room. Actually, the pulsed mode illumination is brighter to the camera than the 100 watts of light from the ceiling light directly overhead! The continuous current LED illumination is also very good, with only a slight fading of the sharp edges and highlights. With no light at all, the camera can still make out a bit of the scene, which is more than I can see with my own eyes. A good low lux camera goes a long way when it comes to night vision projects.



So the verdict is in - pulsed mode operation of infrared LEDs does offer some improvement, but you will have to decide if the added complexity of is worth the effort. Depending on the cost and output power of your LEDs, it may be more effective to simply add more LEDs into your array to achieve a higher output. More LEDs also has the benefit of illuminating a greater field of view, which is why most night vision camera manufacturers are now opting for the more LEDs over pulsed mode operation. The benefit of pulsed mode operation is that less power is consumed due to the pulse duty cycle, and that a brighter illuminator can be made in a smaller space. There also appears to be some gain due to the mysterious light spectrum shifting of running LEDs in pulsed mode as the 940 nanometer LEDs begin to output radiation closer to 840 nanometers if the pulses are very short.
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