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Infrared light's effect on digital photography

Digital sensors are especially sensitive to IR light rays.


The picture on the left is a normal exposure. The other is a daytime long exposure photograph, showing color shift caused by excessive infrared light. Photos courtesy of Stefan Lozinsky.
The picture on the left is a normal exposure. The other is a daytime long exposure photograph, showing color shift caused by excessive infrared light. Photos courtesy of Stefan Lozinsky.

WHERE DID THAT REDDISH LOOK COME FROM?

If you have taken a long exposure during the daytime with your digital camera, you will probably have noticed a reddish color shift in the image and wondered where that came from.

Blame it on infrared light. Digital sensors are not only sensitive to light from the visible part of the spectrum, but are also sensitive - actually very sensitive - to the invisible rays of infrared light, or "IR." When you take a long exposure during the day, you need a long shutter speed which you can achieve through filtration that reduces the amount of visible light reaching the sensor – specifically by attaching one or more neutral density filters and maybe even a polarizing filter to the front of your lens. But, neither of those types of filters has an effect on infrared light, which is permitted to pass through and, because of the long exposure time, build up in the image to the extent that it tends to over-saturate red.

Subjects illuminated by sunlight have the greatest amount of IR radiation. And long exposures in sunlight capture much of that radiation in your images.

You may like the sunrise look caused by infrared light, but the picture doesn't show true colors. Photo courtesy of Stefan Lozinsky.
You may like the sunrise look caused by infrared light, but the picture doesn't show true colors. Photo courtesy of Stefan Lozinsky.

WHAT CAN YOU DO TO GIVE YOUR LONG EXPOSURES A MORE NATURAL LOOK?

This effect can sometimes be corrected after taking your long exposure daytime pictures by downloading them to a computer and using image-editing software.

It can also be mitigated by using an infrared cut-off filter, which might also be called a heat absorbing filter. This filter blocks some infrared light while allowing visible light to reach the sensor. Some people refer to it as an IR filter, but that is probably incorrect. A true IR filter allows infrared light to pass through it while an infrared cut-off filter does the opposite; it blocks infrared light. Heliopan offers a filter especially designed for digital sensors called the "Heliopan Digital Filter" that blocks both UV (ultraviolet) and IR (infrared) light in daylight photography.

SOME IR PROTECTION IS PROBABLY ALSO BUILT INTO YOUR DIGITAL CAMERA

A great many digital cameras - most, in fact - are constructed to block some infrared light to downplay its effect in normal everyday photography, since sensors are so sensitive to infrared. If they weren't protected from it, IR light could adversely affect exposure, focusing and white balance for all of your digital photography, regardless of exposure time. (Note: These blockers can be removed by technicians from some cameras to convert them for photography using infrared for the illumination of their subjects. It is generally an expensive procedure.)


WHAT IF YOU WANT TO TAKE A DIGITAL PICTURE ILLUMINATED BY INFRARED LIGHT?

First, you must be sure that your digital camera is able to take photographs by infrared light. There is a simple test you can perform. For full information, click here on Infrared digital photography.

Photographer Paul W. Faust took this image illuminated by infrared light. Copyright Paul W. Faust.
Photographer Paul W. Faust took this image illuminated by infrared light. Copyright Paul W. Faust.

More of Paul W. Faust’s images can be seen at impressions-of-light.com.

 
Related topics...

Infrared digital photography

Daytime long exposure photography

Neutral density filter

Polarizing filter

Infrared film