When selecting the illumination for a spectral imaging system, three major points must be considered.
Spectral imaging requires much more light than traditional RGB or grey scale black-and-white imaging. The required total illumination power depends on
- the geometry of the illuminating beam and the distance from the sample,
- width of the illuminated target (like conveyer belt)
- the integration time per the image
Need for illumination power increases with
- longer distance to the target
- less illuminating light collimated to the target
- shorter integration time.
The wavelength range of the illumination source
Illumination for hyperspectral imaging must always have a continuous spectrum that covers the full wavelength range of the hyperspectral camera. If the illumination does not have a signal in some of the wavelengths, the measured data on those wavelengths is not valid.
The illumination types compatible with hyperspectral imaging sensors are
- For visible range, most typical is halogen illumination (spots or linear), LED is also used. Supercontinuum lasers show good potential.
- For NIR range: halogen is most typical. LEDs and supercontinuum lasers show good potential.
- For SWIR range: halogen illumination
- For MWIR and LWIR range: thermal illumination
It is important to ensure that the illumination covers the full measurement area with uniform intensity and spectral range, minimum shadows, or specular reflections. To learn more about the illumination for spectral cameras, watch our tutorial video on how to estimate required illumination power for a hyperspectral camera (applies to halogen spot based illumination).