Samenvatting
The legibility of internally illuminated signs is studied in relation to ambient illumination, letter luminance, background luminance and stroke-width. The legibility is impaired by irradiation, when the letters are made too bright, what finds expression in a increase of reading time. Irradiation can be reduced if the background luminance is raised to circa 8% of the letter luminance. By doing so the legibility at day time is not impaired.