30 CFR § 19.9
In addition to the general design and the safety features, MSHA considers
that a lamp of permissible type should meet certain minimum requirements with
respect to performance, as follows:
(a) Time of burning and candlepower. Permissible electric cap
lamps shall burn for at least 10 consecutive hours on one charge of the
battery and shall give during that period a mean candlepower of light beam of
not less than 1.
(b) Bulb life. The average life of the bulbs shall be not
less than 200 hours, and at least 92 percent of the bulbs shall have a life
of 150 hours. The life of a bulb is the number of hours its main filament
will burn in the cap lamp or its equivalent.
The life of a bulb having main filaments in parallel is considered ended when
the first filament ceases to burn; the life of a bulb having independent main
filament is considered ended when the last filament ceases to burn.
(c) Bulb uniformity. (1) The bulbs submitted shall meet the
following minimum requirements for variation in current consumption and
(2) The current consumption of at least 94 percent of the
bulbs shall not exceed the average current by more than 6 percent. The
candlepower (s. cp.) of at least 90 percent of the bulbs shall not fall
short of the average candlepower by more than 30 percent.
(d) Corrosion of contacts. Battery terminals and leads
therefrom, as well as the battery gas vents, shall be designed to minimize
corrosion of the electrical contacts.
[Sched. 6D, 4 FR 4003, Sept. 21, 1939, as amended at 47 FR 11369, Mar. 16,