ISO 24509:2019 pdf – Ergonomics — Accessible design — A method for estimating minimum legible font size for people at any age.
1 Scope This document provides a method for estimating minimum legible font size for single characters, but not for words or sentences, in self-luminous or reflected mode, used in documents, products labels, signs, and displays for people at any age and in any viewing condition in which viewing distance, luminance and contrast are varied. This document applies designing and evaluating legibility of single characters for people at any age who have no pathological disorders in their eyes, but not for people with visual impairments such as low vision. The application is specifically directed to, but not limited to, the cases of printed materials where fixed font size is used. Applicability of the method to other languages is given in Annex F. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 24502, Ergonomics — Accessible design — Specification of age-related luminance contrast for coloured light 3? Terms? and? definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https: //www .iso .org/obp — IEC Electropedia: available at http: //www .electropedia .org/ 3.1 visual acuity V <qualitatively> capacity for seeing distinctly fine details that have very small angular separation <quantitatively> any of a number of measures of spatial discrimination such as the reciprocal of the value of the angular separation in minutes of arc of 2 neighbouring objects (points or lines or other specified stimuli) which the observer can just perceive to be separate
3.3 luminance? correction? coefficient coefficient for correcting the effect of luminance on visual acuity (3.1) relative to the acuity at the 100 cd/m 2 level 3.4 minimum legible font size character size, expressed in unit of point, for a single character under which the character is not legible with less than 80 % probability at the specific viewing condition Note 1 to entry: The unit of point is defined in this document as 1 pt = 0,351 4 in, which is used mainly in the US and Japan. Another definition is 1 pt = 1/72 inch = 0,352 77 in, mainly used in the EU. The difference is too small to have any influence on legibility. Note 2 to entry: Minimum legible font size is a baseline of legibility and not at the comfort level of legibility (see Annex H) 4 Application conditions For the application of the method for estimating the minimum legible font size, the following viewing conditions shall be specified: a) age: the age of a person shall be from 6 years old to 90 years old; b) viewing distance: the viewing distance shall be between 0,2 m and 100 m; c) luminance: the luminance shall be between 0,01 cd/m 2 and 3 000 cd/m 2 . NOTE Luminance means the luminance of the surrounding area, not of the font, for the positive font type where a character looks darker than the background. In case of negative font type, where a character looks lighter than the surrounding area, luminance means that of the character. d) contrast: the contrast, positive or negative, shall be between 0 % and 100 %, defined by Michaelson Contrast (see NOTE in Clause 6). 5 Estimation of minimum legible font size The minimum legible font size shall be calculated by the following procedure. Calculation examples and application are given in Annexes C, D and E. a) Select a visual acuity, V 0 , at the luminance level of 100 cd/m 2 for a specified observer’s age and for a specified viewing distance from Annex A.