4.28.3* Visual Alarms. Visual alarm signal appliances shall be integrated into the building or facility alarm system. If single station audible alarms are provided then single station visual alarm signals shall be provided. Visual alarm signals shall have the following minimum photometric and location features:
(1) The lamp shall be a xenon strobe type or equivalent.
(2) The color shall be clear or nominal white (i.e., unfiltered or clear filtered white light).
(3) The maximum pulse duration shall be two-tenths of one second (0.2 sec) with a maximum duty cycle of 40 percent. The pulse duration is defined as the time interval between initial and final points of 10 percent of maximum signal.
(4) The intensity shall be a minimum of 75 candela.
(5) The flash rate shall be a minimum of 1 Hz and a maximum of 3 Hz.
(6) The appliance shall be placed 80 in (2030 mm) above the highest floor level within the space or 6 in (152 mm) below the ceiling, whichever is lower.
(7) In general, no place in any room or space required to have a visual signal appliance shall be more than 50 ft (15 m) from the signal (in the horizontal plane). In large rooms and spaces exceeding 100 ft (30 m) across, without obstructions 6 ft (2 m) above the finish floor, such as auditoriums, devices may be placed around the perimeter, spaced a maximum 100 ft (30 m) apart, in lieu of suspending appliances from the ceiling.
(8) No place in common corridors or hallways in which visual alarm signalling appliances are required shall be more than 50 ft (15 m) from the signal.
Depending upon what document your jurisdiction uses for accessibility guidlines (ADAAG or ANSI A117.1), it will be what Roger stated or (assuming a wall mount) the ANSI standard of 80"-96" A.F.F., measured to the bottom of the device.
I believe that there are more states that enforce the ANSI than states that enforce the ADAAG.
Ron: Thanks for the input. I don't have a copy of the NFPA 72 because it is out of my jurisdiction, I leave it to the fire marhall. I call this out on plan review often and have been told by EE's that the 72 has a different elevation. Thanks for the correction.
Bob: I don't have the ANSI here at the house so I'll back this up on Monday, but I believe for a ceiling mount you are permitted to go up to the ceiling as long as it is not more than 30(?) feet A.F.F.