Bright is Bright Enough?
A Comparison of Infrared Light Sources
The following discussion is about use of IR lights with video cameras. See Working with Night Vision Technology for information on night vision goggles and infrared illumination.
If you purchased a Sony NightShot camcorder and tried it out, you discovered that the built-in IR light doesn't give much of an image except at very short range. So maybe you looked at Sony's accessory catalog, and ordered their high brightness infrared light that is advertised for viewing to 100 feet. Again you tried this out, and may still have been disappointed. You certainly couldn't see your subject at 100 feet, unless it was very large. What's wrong? Is this technology just not up to expectations? The answer is that you still do not have sufficient illumination to utilize the full capabilities of the Nightshot feature, even with the supplementary light from Sony. In short, the camera is just fine, you merely need more light.
So how do you know when your IR light is bright enough?
This is easy to answer if you know exactly what your subject is and exactly where it is. You have sufficient light if the entire subject is visible and details are clearly seen. This is a function of the size of the subject and its distance from the camera. It is harder to answer if you're not sure what or how many things you're looking at. One of the problems with inadequate lighting is you don't realize how much you are missing until you compare the scene using better lighting (as we illustrate below).
For example, when your job is to count bats exiting from a mine entrance, you need to be able to see the entire entrance area, and you need enough light to clearly see and distinguish each and every individual bat. For an entrance about 2 ft by 3 ft, with the camera only 5-6 ft away, the Sony accessory infrared light may be sufficient. However, for larger mine entrances, where the camera must be farther away, and for many other wildlife applications, the Sony light is probably insufficient. You may still see bats, but you will also fail to see bats that are there, and your count will be inaccurate. The only real way to ensure sufficient lighting is to keep adding brighter light until you no longer see an improvement in image quality. For guidelines, see [Setup Considerations when Filming with IR Light].
The following three images illustrate the differences between light sources. The scene is an abandoned mine portal, about 10 by 5 ft. The distance from the camera to the portal is about 20 feet.
|Illuminated only with the built-in LED illuminator of the Sony Camcorder. This light is generally not usable beyond a few feet.|
|Illuminated with the accessory Sony infrared lamp (model HVL-IRC). You can just make out a few bats flying in the portal.|
|Illuminated with our IRLamp6. You can now see that there were actually quite a few more bats than were revealed in the images above.|