BASIC CONCEPTS OF RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 18

Out-of-band radiation is another problem encountered in performing action
spectroscopy and in measuring light sources. The term used for out-of-band radiation
from a monochromator is stray light, and is illustrated in Figure 10. Stray light poses a
serious pitfall when attempting to measure a weak spectral signal near a strong spectral
signal, for example in attempting to measure a tungsten lamp at 300 nm or sunlight at
300 nm. 11-12 The monochromator slit function defines the degree of stray light in a fixed
wavelength. This is hopefully less than 0.1%. One normally concludes that the best
action spectroscopy and the best spectroradiometric measurements with a
monochromator should be performed with a narrow bandwidth. This may be slow but
should offer more detail. This is clearly more important when a source or action
spectrum is rapidly changing. While it is true that the choice of wider bandwidths will
allow more energy through the monochromator and allow for a faster measurement or a
faster exposure, it offers less detail and can only be used with a source that has a very
slowly varying spectrum.
Figure 10. The effects of stray light.