A common way to measure a camera sensor’s spectral response is to illuminate it with narrow-band light across the wavelength range of interest and record the sensor output at each wavelength. A typical lab setup uses:

• a monochromator to select wavelength
• an integrating sphere (light sphere) to provide uniform illumination
• a calibrated photodiode as a reference detector

You then compare the camera’s response to the reference measurement as you step through wavelengths and build the response curves. Simpler approaches can also use diffraction gratings, but they are generally less controlled than a monochromator-based setup.

There are commercial systems made specifically for this kind of camera characterization as well.

One important distinction: spectral response is not the same as broad “color sensitivity” scores such as DxOMark’s color depth in bits. Those summarize how well a camera distinguishes color tones, but they do not provide the underlying wavelength-by-wavelength spectral response curves.