Led Red

How do I measure the wavelength of a red LED?

I need to find a relatively cost effective way to measure the wavelength of colored LED lights red. I have to try several to find the wavelength, and then buy more red LEDs, and measure them to continue that fall within my range of length wave, and discard the others. This is a machine that picks up the red light of a relatively specific range, and LEDs have now lost their force (many of them are from the 90s, some even more). I have to replace the existing LEDs compatibility with other wavelength. Moreover, according to my explanation, the red LED weakened the force would still have the same wavelength of light, but with less intensity, right? Thank you very much to anyone who can help me with this!

You may be able to buy a diffraction grating for a reasonable price.

Led Red

Led Red