161.013-5—Intensity requirements.
(3)
Have a minimum Equivalent Fixed Intensity within a vertical divergence of ±3 degrees of at least 15 cd.
(1)
Have an Equivalent Fixed Intensity of no less than 25 cd within ±4 degrees vertical and ±4 degrees horizontal divergence centered about the peak intensity; and,
(c)
The Equivalent Fixed Intensity (EFI) is the intensity of the light corrected for the length of the flash and is determined by the formula:
Code of Federal Regulations
Where:
I is the measured intensity of the fixed beam,
tc is the contact closure time in seconds, (0.33 for this S-O-S signal), and
ti is the incandescence time of the lamp in seconds.
(d)
An electric light which meets the requirements of either paragraph (a) or (b) of this section need not, if capable of operating in both manners, meet the requirements of the other paragraph.