November 26, 1915.

THE COLLIERY GUARDIAN.

1081

ILLUMINATION OF MINES.*

By Robert P. Burrows.

The lighting of a typical coal mine may be divided
into four distinct parts :—(1) The lighting of the build-
ings about the top; (2) the lighting of the working
faces; (3) general illumination at the bottom; and (4)
special applications of lighting.

The lighting of buildings about the top may be treated
in the same manner as that of any other industrial
plant, for we have a boiler room, an engine and
generator room, a forge, a machine shop, and a hoist
room. These can be well and efficiently lighted by the
use of 100-watt tungsten-filament multiple lamps, with
proper reflectors, so spaced and suspended that a power
consumption of from J watt per square foot in the
boiler room to 1 watt per square foot in the machine
shop is obtained. The methods that apply to this kind
of lighting have been ably treated by a number of
authors, and for this reason a detailed discussion is
unnecessary.

The lighting of the working faces is usually done by
means of portable lamps, of which there are four types

Fig. 1.—Typical Mine Layout.

in use :—The oil torch, the acetylene lamp, and the oil
and the electric safety lamps. The different types have
been fully described in numerous papers and articles,
and need not be dilated upon. Figures on the cost of
operation would be of interest, but very few such data
are obtainable, though they would be of particular
benefit in view of the advent of the electric safety lamp.

The oil torch is without question the cheapest source
of light. The acetylene lamp, at a cost .of 6c. to 10c.
per lamp per week, gives far superior illumination, but
the characteristics of this source of light as well as any
other open-flame lamp will bear careful consideration
in view of the ever-present desire for industrial efficiency
and safety. It is the opinion of many that the greater
percentage of disastrous explosions in the United States
have resulted from the use of open-flame lamps in the
so-called non-gaseous mines. This question of safety,
of course, merits serious consideration.

The oil safety lamp has a distinct advantage in that
it gives an indication of the presence of gas. Its develop-
ment marked one of the greatest advances in mine
lighting, although in most cases at the present time it
is not considered a guarantee against explosion when in
the presence of gas. Figures obtained from other
countries indicate the cost of using oil safety lamps is
from 7c. to 9c. per lamp per week.

The electric lamp gives a steady and readily directed
light, free from gases, soot, and frequent outage. A
large proportion of the generated light is directed on the
working face. It is sometimes considered a disadvan-
tage that the electric safety lamp does not give an
indication of gas as does the oil safety lamp. The trend



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Fig. 2.—Well-lighted Shaft Bottom.

of opinion in England, however, is toward choosing a
lamp for the light it gives, and to use some other means
for gas indication. There is no question that an electric
lamp passing the tests of the United States Bureau of
Mines will give more light on the working face than any
of the three previous illuminants, because it has been
scientifically designed with that end in view.

Electric light costs from 12c. to 17c. per lamp per
week. This cost is about twice that of the oil safety
lamp, but the light on the “ face ” is materially
increased. One electric lamp manufacturer places the
cost of electric light at 2Jc. per lamp per shift. This
figure, though it seems low, can well be realised with a
large installation and proper care. In this connection,
it is very necessary to have proper housing and proper
attention for electric lamps—more so than with the oil
safety lamps. It has been found that this care and
attention is very little, if any, more expensive than

* From a paper read before the American Institute of
Mining Engineers.

that given to oil safety lamps, even though more expen-
sive help is needed, because fewer men are required to
care for the electric outfits. The United States has been
slow in taking up the electric lamp. It has been said
that in Belgium alone there are 12,000 outfits in use.
The excellent work done by the United States Bureau
of Mines to obtain the highest efficiency for this new
source of illumination has accomplished what years of
competition among electric mine lamp manufacturers
could hardly have brought about.

The application of the principles of industrial illumina-
tion to the general lighting of mines must be made in
the face of conditions difficult to overcome. In fact, all
the conditions the illuminating engineer considers most
difficult are present—low ceilings, black walls, dust,
smoke, and dampness; but in spite of these, very satis-
factory results have been obtained.

From a lighting standpoint, an ordinary mine can be
considered as composed of at least six parte; the bottom,
the run around, main entry, side entries, mule stables,
and small rooms, such as offices, pump rooms, storage
rooms, and first-aid rooms. These are shown diagram-
matically in fig. 1. The bottom, being the entry and
exit for both men and coal, accommodates more traffic
than any other part of the mine, and should be especi-
ally considered from the standpoint of both convenience
and safety. Fig. 2 shows a portion of a well-illuminated
bottom and shaft opening of a typical mine. The light-
ing of the shaft in this case was accomplished by the
use of 40-watt tungsten filament lamps, equipped with
angle reflectors, placed above and across the shaft open-
ing, so as to direct the light on the cages. The maximum
intensity is at the near edge of the cage, and the eyes of
the workmen on the side of the shaft toward the
observer are not subjected to the glare of the lamps.
For comparison, fig. 3 shows this same portion of the
mine lighted by the use of bare carbon lamps. It will
be seen that the distribution is not of the best, and also
that the glare of the bare lamps obscures that portion of
the mine which lies beyond. These illustrations were
made from actual photographs, retouched only enough
to remove the halation effects of the bare lamps. The
photograph shown in fig. 2 was exposed about one
minute, as against 15 minutes for the one in fig. 3.

Fig. 3.—Poorly-lighted Shaft Bottom.

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That portion of the bottom leading into the mine,
where cars are directed on to the cages, can be well
lighted with 40-watt tungsten lamps in shallow dome
reflectors placed above and between the tracks. These
units, spaced at about 6 ft. intervals, and hung about
8 ft. above the floor, will give satisfactory distribution
of light. It will be noticed from fig. 4 that the ear
wheels are well illuminated, and that there is practically
no glare. It would be well to design the lighting of
this part of the mine on a basis of 4 to 5 foot-candles at
the floor, not because the work demands this intensity,
but because of the greater safety which results from
ample illumination, and because dust collecting on the
lamps and reflectors decreases the amount of light
delivered.

The run around should require only sufficient light to
make visible any obstructions in the path of the empties
as they leave the cages. This part of the mine may be
illuminated with 25-watt tungsten lamps, equipped with
shallow dome reflectors, spaced 15 ft. apart, and sus-
pended 8 ft. above the floor. In the main entry the
function of light is not so much to illuminate as to
silhouette objects which may obstruct the passage way.
With silhouette lighting, a comparatively small amount
of light is needed to obtain the effect desired, which is
to see objects outlined against something that is lighted.
For instance, whitewashed doors or walls reflecting the
light toward the observer’s eye are excellent backgrounds
against which objects form silhouettes when in the line of
vision of the observer. The glint of the light on the
rails forms another good surface from which silhouette
lighting may be obtained. With 25-watt tungsten lamps
in shallow dome reflectors, spaced at intervals of about
300 ft., the height depending upon the height of the entry,
the silhouette lighting is excellent. Two units, one to
illuminate the switch and the junction, and the other
illuminating a portion of both the main and side entries,
help to eliminate collisions, and, by the increased light,
warn the trip driver that his train is approaching such a
j unction.

The stables, with their low roofs, may be effectively
lighted with 40-watt tungsten lamps equipped with angle
reflectors placed along the back wall, and as high as
possible, one unit to each two stalls. In front of the
stalls, and opposite the angle units, 25-watt tungsten
lamps with deep bowl reflectors may be used to illumi-
nate the feed boxes and passage way.

The mine offices need but one 25-watt tungsten lamp
equipped with a shallow dome reflector. The fireboard

at the bottom should be well illuminated with one or
more 25-watt lamps of this type, equipped with angle
reflectors, depending upon the size of the board, while
the pump rooms and storage rooms may be lighted in
the same manner as offices.

The first-aid rooms, in order that the best attention
be given the injured, should not only be well lighted,
but should have the walls well whitewashed, thereby
obtaining well diffused and distributed light. Frequent
whitewashing of the walls of the bottom, offices, stables,
etc., and the walls of the entries for 20 ft. each side of



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Fig. 4.—Properly-illuminatkd
Entry.

the units, will greatly increase the illumination in these
parts of the mine. Carbon lamps are most generally
used in mines, but to keep the load on the generator as
low as possible, and maintain the most constant illumi-
nation in spite of voltage fluctuation, and to direct the
light where wall and ceiling reflection cannot be relied
upon, tungsten filament lamps with weatherproof
enamelled reflectors will probably, be found most satis-
factory.

It may be interesting, by reason of the high voltage
usually found in mines, and its fluctuation, to show how
the proper voltage for a lamp, to secure greatest life and
light, is determined. A recording voltmeter is con-
nected at the switchboard on the terminals of the switch
controlling the lighting circuit, usually the trolley line.
When this is in operation, a carefully calibrated portable
voltmeter is connected in multiple with the recording
meter, and a section of the chart of the recording meter
is compared with the readings of the calibrated portable
meter. This chart should be taken over a period of at
least three hours, and for 24 hours if possible.

Lamp Voltages for Various Line Voltages. Street-
railway Tungsten-filament Lamps.

Average line	No. of lamps	Voltage of
voltages.	in series.	individual lamp.
250	2	120
260	'.	2	125
270	2	130
280	2	135*
290	2	140*
300	3	105
325	3	105
350	3	115
400	3	130
425	4	105
450	4	110
475	4	115
500	4	120

For voltages above 500, use five lamps in series as on
street-railway circuits.

* Special lamps.

Voltage readings are then taken back from the shaft
along the main entry at intervals of 300 or 400 ft. by

6 100-

120

c
<i> 80

CANDLE POVfE/t CHARACTERISTICS
OF

INCANDESCENT LAMPS

O
a- 120

100

Per Cent Vo 1 ts

Fig. 5.—Candle-power Characteristics of
Incandescent Lamps.

means of the portable meter, the voltage and time being
recorded. A study of the chart will show the average
voltage over the period taken. A comparison of the
chart with the voltage readings taken back in the mine
will show the average drop in the line. From the
average voltage obtained from the chart should be sub-
tracted the average line drop obtained from the readings
taken in the mine, the result being the voltage on which
lamps will operate to give the same life as on the
fluctuating voltage in the mine.

For average voltages up to 250 volts, regular multiple
lamps should be used. For average voltages from 250
up to 280 volts, there is a choice of burning lamps in