4 LANGFORD'S ADVANCED PHOTOGRAPHY printing digitally or from film. Cards and charts should be reintroduced whenever the lighting changes. Colour temperature meters In a neutral-coloured studio with standardized and matched lighting, results can be predictable. On location it is often only necessary to control the colour temperature of the predominant light on the principal subject. The colour temperature variances of the background can be tolerated and will often retain or enhance the atmosphere of the location. However, where highly accurate colour reproduction is essential for packaging, clothing, artworks and so on, the colour temperature of light sources can be measured with a meter (see page 11). Note that the colour temperature meter is designed to read continuous spectrum light sources. It will give rogue readings of sources such as fluorescents, lasers or most sodium or mercury vapour lamps because they all emit lines or bands of wavelengths with gaps in between (Figure 1.11). This confuses the meter's sensors. Practical control of colour