In older facilities, we see illumination for an exit sign coming from an external source. Section 1013.6 of the IBC regulates the graphics, illumination, and emergency power supply for such signs.
Although no particular color is specified for exit signs, it is REQUIRED that the color and design of the signs, the lettering, the arrows, and other symbols on the sign provide good contrast to increase legibility. The letters of the word EXIT MUST BE AT LEAST:
- 6 inches in height and
- have a width of stroke of not less than ¾ inch
By specifying the letter spacing, the code ensures that the letters are not placed too close together and that the signs will be legible and more effective as a result. Additionally, when a larger sign is provided, it is important the lettering be increased proportionally.
When the illumination of the sign is from an EXTERNAL SOURCE, that source must be capable of producing a light intensity of at least 5 foot-candles (54 lux) at ALL points over the face of the sign. Measurement of the 5 foot-candles from an external source can be made by a light meter.
The measurement of the equivalent luminance, however, from an internal source is more difficult. The code relies on a nationally recognized testing laboratory (NRTL) that has examined, certified, and labeled the exit sign. In labeling such a sign, the testing agency is certifying, among other things, that the light level is at least that required by the code.
Externally illuminated exit signs are required to be illuminated AT ALL TIMES and must provide continued operation for a minimum of 1.5 hours after the loss of the normal power supply. This backup power supply shall be from a complying
- storage battery system,
- unit equipment, or
- other approved on-site, independent source
The exception addresses illumination provided independent of external power supplies and, therefore, does not require compliance with the emergency power provisions.