Which Infrared Filter Do I Have?
How do you know what type of infrared filter you have if you have an unmarked filter or if you purchased a used converted camera? Use this guide to help you identify the type of IR filter you have.
The short answer: display a rainbow gradient of the visible spectrum on your monitor, photograph it through the filter or with the converted camera, and see which colors survive. A filter blocks everything below its cutoff, so the colors that remain tell you roughly where the cutoff is. If green through red survive, it’s about 550 nm. If only orange and red survive, it’s about 590 nm. If only red survives, it’s 695 to 720 nm. If the screen goes completely black, it’s above 750 nm.
How the Test Works
You need a calibration image. Mine is a plain Photoshop gradient fill that runs through the colors of the visible light spectrum, from violet and blue on one end to red on the other. You can make your own or download mine with the button above.
Open the image full screen on your monitor, point the camera with the filter at the screen, and take a shot. Then compare it to the original gradient.
A monitor only emits visible light. It doesn’t display infrared or ultraviolet, so this test can’t show you what a filter does beyond red. What it does show is where the filter starts blocking visible light, and that is enough to identify most filters.
Two things to watch for:
- Ignore the red on the far left edge. Color software treats hue as a 360 degree circle, so a little red blends into the magenta end of the gradient. Red showing up on the far left doesn’t mean the filter passes magenta. It’s the same red light that is passing on the right side.
- Keep window light off the screen. Sunlight carries infrared, and a window reflected in the monitor shows up in the shot even when the screen itself is black.
Reading the Results
Full Spectrum or Hot Mirror
Every color in the gradient appears. A full spectrum camera shows the full range, and so does a regular visible light camera with its standard hot mirror filter.
550 nm
Blue, cyan, and violet are gone. Green, yellow, orange, and red all pass, and green takes up a wide band. A 550 nm filter passes green and everything to the right of it. For more on this filter, see The Orange Filter, 550 nm Infrared Filter.
590 nm
Green and yellow are now blocked too. The brightly exposed part of the gradient is just orange and red. A 590 nm filter blocks yellow, green, cyan, blue, indigo, and violet, and passes only orange and red.
695 nm to 720 nm
The image turns nearly monochrome. Only one visible color comes through, red. When red is the only visible color left, you have a filter somewhere between 695 nm and 720 nm. After a white balance, that red reads as white and the rest of the image has very little color.
800 nm and Higher
The screen is black. The camera records only infrared, and the monitor emits none. The only things you’ll see are the edge of the monitor and any reflected window light. This tells you the filter blocks all visible light, so it’s something above about 800 nm, most likely an 830 nm or 850 nm, or maybe a 900, 950, or 1000 nm filter. The test can’t tell those apart.
IR Chrome
This one looks different from all the others. Blue, cyan, and green pass, but violet and indigo at the far left are blocked, and so are yellow, orange, and red. The IR Chrome filter is a dual band pass filter. It passes a slice of blue to green visible light, blocks the middle of the spectrum, and passes infrared, which this test can’t show.
That combination explains the IR Chrome look. The blue sky comes through as blue without a color swap. Foliage reflects both green and infrared light, and the two combine into the orange and red tones. For more on this style, see the IR Chrome Infrared Filter Review.
Summary
| What survives in the test image | Likely filter |
|---|---|
| Every color | Full spectrum or hot mirror (visible light) |
| Green, yellow, orange, red | 550 nm |
| Orange, red | 590 nm |
| Red only | 695 nm to 720 nm |
| Nothing, screen is black | 750 nm or higher (830, 850, 900+) |
| Blue, cyan, green, nothing warmer | IR Chrome (dual band) |
Related
- Infrared Filters: Color Doesn’t Exist Audiobook Sample
- Full Spectrum Plus Filter Compared to Converted to Filter
- White Foliage Infrared
- 665 nm Infrared Filter
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