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Could illuminating a subject with different LEDs be used instead of bandpass filters?

I am experimenting with capturing surface reflectance using a monochrome camera. The traditional approach to capturing specific reflected wavelength bands is to take multiple photos each with a bandpass filter in front of the camera which only allows a small band of light wavelengths pass.

I will be capturing photos under very controlled lighting, all external light sources will be blocked and the subject will be surrounded by an array of LEDs.

I understand that you can't just use white or RGB LEDs as they will only emit in three different bands. A full spectrum of LEDs emitting at different bands would be needed.

Here is a good chart showing individually available LEDs and their wavelengths: https://www.lumex.com/article/led-color-guide

If this could work the main advantage would be eliminating the need to mechanically change the filters which in turn would eliminate vibrations and speed up the capture process. Probably also reduce costs.

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Yes, this would work. But whether you want to do so would also depend on the wavelength resolution you need. An LED emission band can be rather large (perhaps ~10's of nm), and you could probably do better with specialized bandpass filters. More to the point, you have a lot more flexibility if you use bandpass filters, including the flexibility to purchase quite narrow or sharply-defined (i.e. steep cut-off/on) lines. LED emission probably won't be quite so clean. At the very least, you should request the emission spectra of the LEDs before you commit to them so you can see what you're working with. But given the right requirements, it could totally work! Have fun!

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  • $\begingroup$ Thanks for your input and validation, greatly appreciate it! Yeah we'll have to do some experiments and see if LEDs can be found with appropriate bands for our needs. Looks like LEDs have come a long way in the last couple of years. We're creating a portable multispectral camera rig and swapping filters will add bulk to the rig and time to the capture process, so I'm prepared to deal with the nuances of LED light. $\endgroup$ – Geordie Jun 4 '18 at 17:43

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