(a)Design. In the determination of the adequacy of the lamp,
with respect to design, the following points will be considered: (1) The
materials used; (2) construction; (3) weight; (4) amount of light; (5)
distribution of light; and (6) exclusion of dust from the headpiece. The
suitability of the materials and the construction shall be determined by
preliminary inspection, by dropping tests,1 by durability tests of
the cord and cord armor,2 and by the general behavior of the lamp
equipment during the investigation. The amount and distribution of the light
shall be judged both by observation of the illumination on a white screen
and by photometric measurements.
1 Batteries are dropped 3 feet, at least 20 times onto an oak floor.
Headpieces are dropped 6 feet, at least 20 times, onto concrete.
2 Ten cords, assembled with the cord armor and outlet of the lamp
with which it is to be used, are slatted at least 100,000 times through an
arc of 50 degrees at approximately 90 slattings per minute.
(b)Angle of light beam. MSHA recommends that the angle of
the light beam be at least 130 degrees horizontally to insure that the
contrast edge of the beam is away from the more sensitive sector of the
wearer's vision; however, to allow for manufacturing and assembly tolerances
and the use of multiple filament bulbs, MSHA will approve lamps giving a
minimum beam angle of 120 degrees. If the bulb has more than one major
filament, the one giving the smaller angle will be used in the
determination.
(c)Light distribution, visual. Excepting special headpieces
for inspection purposes, the area illuminated by the beam shall be free from
sharp gradations in light intensity and spectral shadows.
(d)Light distribution, photometric. (1) Excepting special
headpieces for inspection purposes, the maximum candlepower of the light beam
shall not be greater than 25 times the average or mean candlepower of the
beam.3
3 The minimum allowable angle of 120 degrees will be used in
determining the mean candlepower of the beam.
(2) The minimum candlepower of the beam based upon
readings at the design voltage of the bulb shall not be less than 1.
