Evaluation of Light Measurement Instruments

The International Standards Organization (ISO) defines standards to ensure that viewing conditions are consistent when evaluating printed samples through ISO 3665 (2009), Graphic technology and photography – viewing conditions. The need for this standard stems from the necessity for human visual assessment as the key arbiter of the quality of complex images, and the tendency for various lighting conditions to shift the appearance of a color, specifically in relation to other adjacent colors. Among the conditions specified by ISO 3665 (2009) are Correlated Color Temperature (CCT) and Color Rendering Index (CRI). CRI is expressed as CRI Ra, with Ra representing the international standard for CRI as defined by CIE 13.3-1995. Both CCT and CRI Ra are quantifiable by a range of instruments, including traceable Spectroradiometers specifically designed for the purpose, general-use Spectrophotometers that can read CCT and CRI Ra, and handheld instruments designed for photographic applications that measure CCT. The present study seeks to compare readings from a traceable Spectroradiometer with those from various other meters across a range of seven viewing booths, some of which are known to be out of specification. The goal is to ascertain how much variance can be expected when using these varied meters when compared to a traceable benchmark instrument