The Effect of Colour and Luminance on the Lightbox Wayfinding Sign Legibility in Metro Stations

Lightbox luminance and colour play an important role in improving the legibility of metro directional signs. However, there are currently no relevant design and technical standards. This study examined the effect of lightbox colour and luminance on wayfinding sign legibility. First, a set of levels for the background luminance of the lightboxes was proposed. Second, based on the perceived brightness magnitude, test points and luminance thresholds were determined under different background luminance levels. Visual acuity tests were then performed using a white Landolt C with different luminance values on different sign backboard colours under varying background luminance levels. The results indicate that both lightbox colour and Landolt C luminance impacted legibility, with the latter exhibiting a greater effect. Wayfinding sign legibility with the same luminance increased significantly with higher background luminance. Moreover, legibility differed substantially between achromatic and coloured lightboxes: the average acuity of coloured lightboxes was lower at low background luminance, whereas the opposite was true at high background luminance. Accordingly, minimum luminance thresholds were proposed according to lightbox colour and background luminance based on an average acuity of 95%. These findings provide an important reference for luminance control of different coloured lightboxes in metro stations.