Detectors and light sources form the basis for any application of light technology and optical devices. Frequently used devices are spectrometers, which allow a spectral characterisation of the light sources. The following overview provides a brief introduction to the topic, for detailed questions, please refer to further textbooks and original publications. First, detector principles and selected detectors are described. Then, we discuss their use as single detectors or within focal plane arrays. Second, two general types of light sources are introduced and respective common light sources are presented. Finally, the issue of eye safety while using intense light sources is discussed.