Scientific Photography and Applied Imaging

4 Light and radiation sources

4.1 Introduction

The processes of photography and imaging usually require a source of light (illuminant) or radiation to illuminate or to irradiate the subject, respectively. The subject itself may be luminous (‘bright’) by emitted light or radiation, such as the sun, stars, flames and radioactive sources. The subject and its surrounding environment or scene may be recorded with a ‘mixture’ of direct light and radiation from illuminants, by emitted light and ambient light, usually with one of these being dominant.

The spectrum of electromagnetic radiation (EMR) is divided into bands or zones by wavelength (λ), see Figure 4.1. The nominal 400-700 nm band is visible light, quantified by photometric units, otherwise ...