Layout of templates for creation of graphical symbol originals
The recommendations given in this annex are applicable to signs other than escape route signs. Recommendations regarding sizes of escape route signs are given in Part 3 of this Standard.
B.2 Size vs. viewing distance formula
In order to decide on the minimum size of sign needed, the maximum viewing distance at which the sign is required to be conspicuous and intelligible has to be determined. The viewing distance at which a sign of a particular size is conspicuous and legible depends on the illumination of the sign. The sign height h, in millimetres (mm), needed for a particular viewing distance can be calculated from the following equation:
D is the required viewing distance in millimetres (mm)
Z is a distance factor to take account of the illumination of the sign and the amount of detail it contains
Table B.1 gives sign heights (as defined in ? and illustrated in Figure ?) calculated for various maximum viewing distances in adequate (50 lux) vertical illuminance at the sign. These are based on a value of Z = 120 which takes account of the level of illumination and the need to comprehend a graphical symbol where the size of the critical detail is not less than 1/19th of the sign height. For text only signs, a value of Z = 225 should be used.
If a sign is brightly lit or is internally illuminated at all material times a smaller size than that given in Table B.1 would be acceptable.
Conversely if the sign is poorly lit or has complicated detail, a larger sign would be needed.
|Table B.B1 ―
||Minimum sign heights recommended for different maximum viewing distances
|Maximum viewing distancea
|Minimum sign heightb
|Recommended letter heightc in supplementary text sign
|a Calculated using formula X with Z = 120 and rounded down to the nearest whole metre.
b For intermediate viewing distances the next largest available sign height should be used.
To be developed