The Impact of Shop Sign Luminance Contrast and Density of Background Light on Visual Saliency: A Case Study in Yaowarat Road

Advertising and shop signs in nighttime commercial area play an important role in attracting customers. Each sign creates not only an identity to the shop itself but it should also be outstanding among the others from various views. A current outdoor lighting guideline (ILE, 2005) recommends an appropriate luminance contrast ratio according to the level of distinction. The recommendation indicates luminance contrast ratios for only an object in front of a uniform background. However, at nighttime in urban areas always have various complicated background light. The aim of this study is to find appropriate ratios of luminance contrast in various densities of background light patterns which have an impact on visual saliency of shop signs. The study was conducted by reproducing a photo from an actual location in Yaowarat area and adjusting the density of background light and luminance contrast in nine different pictures by using Adobe Photoshop program. Subjects were asked to rate the saliency value of each picture. The result analyzed by using statistical method of ANOVA showed that the density of background light, luminance contrast and the relationship between the two variables (density of background light x luminance contrast) had an impact on visual saliency of the target sign significantly (p<0.01). The average mean of the saliency value increased when the luminance contrast increased. However, it decreased when the density of background increased. The mean of medium background density was the lowest due to the tension of elements in the picture which acted as an extraneous variable.