Light in standardised insect photography and description of lighting devices, including the UV range

Abstract

Digital photography has become indispensable in many areas of biology and plays an essential role in digitization in museums and for the analysis of traits of organisms. The aspect of lighting quality has received surprisingly little attention so far, although good colour rendering is an important criterion. This paper provides an overview of the light quality of various lighting systems in three natural history museums. Light quality is usually expressed by the Colour Rendering index. Here, the relatively strict CIE (International Commission on Illumination) Re index, based on the matching of 16 colours, is used. It presents three self-developed lighting devices with different designs: a light cylinder (also suitable for UV photography of individual objects), a light box for photographing entire insect boxes and a light hemisphere for photographing specimens with reflective surfaces. No light source measured in the natural history museums in London and Berlin achieves an Re index value of >90. Compared to daylight (Re index 98–99), modern daylight LEDs perform best in the new equipment presented (Re 97–98). Existing LED lighting systems sometimes have very pronounced blue peaks and inequalities in the spectrum. The Re values are in the range between 45 and 82. Xenon light sources (such as flash units) show a balanced spectrum (Re index 87). Devices with fluorescent tubes (mercury vapour) achieve Re values of 65 to 84. The new devices ensure shadow-free and homogeneous illumination (deviation of the measured irradiance in the area < 5%) and the respective objectives (suitability for photography in the UV range, photography of entire boxes, low-reflection photography) are achieved. The paper shows some astonishing deficits in light quality in the photography and digitization of insects, which very probably also apply to other areas in biology and beyond. Digitization programs should always check the quality of their lighting and incorporate better light sources if necessary. LEDs with daylight quality are readily available and represent a high-quality alternative. Capturing colour patterns in the UV range enables the documentation of a biologically essential component of the electromagnetic spectrum. It should therefore play a far greater role in digitization programs as well as in ecological analyses.

Keywords

• Digitalization
• light accuracy
• light quality
• lig