When the incandescent lamp was first well established commercially, the useful life of a unit, when operated at 3.1 watts per candle, was about 200 hours. The improvements in the process of manufacture have been continuous from that time until now, and the useful life of a lamp operated at that efficiency to-day is in the neighborhood of 500 hours. Experiments in the treatment of the carbon filament have led to the introduction of the gem metallized filament lamp. This lamp should not be confused with the metallic filament lamps, to be described later, because the material used is carbon, not a metal. As a result of special treatment the carbon filament assumes many of the characteristics of a metallic conductor, hence the term metallized filament. The word graphitized has been proposed in place of metallized.

Table II. * Data On The Gem Metallized Filament Lamp

Watts

Horizontal C. P.

Watts per Candle

+SPHERICAL

Reduction Factor

Useful Life

10

16

2.5

.816

450 hrs.

50

20

2.5

.825

450 "

80

32

2.5

.816

450 "

100

40

2.5

@

460 "

125

50

2.5

@

450 "

187.5

75

2.5

@

450 "

250

100

2.5

@

450 "

* These lamps are normally rated at three voltages, 114, 112, and 110 volts, but data referring to the highest voltage only are given.

+ By spherical reduction factor is meant the factor by which the horizontal candle-power must be multiplied to obtain the mean spherical candle-power.

@ The larger units are almost invariably used with reflectors, hence no spherical reduction factor is given.

The life of the lamps when operated at the lower voltage is increased to about 950 hours, and the efficiency is changed to 2.83 watts per candle.

DINING ROOM IN HOUSE FOR MR. W. F. DUMMER AT CORONADO BEACH, CAL.

DINING ROOM IN HOUSE FOR MR. W. F. DUMMER AT CORONADO BEACH, CAL.

Pond & Pond, Architects, Chicago, I11.

Curly California Redwood Wainscoting.

LIVING ROOM IN HOUSE FOR MR. W. F. DUMMER, AT CORONADO BEACH, CAL.

LIVING ROOM IN HOUSE FOR MR. W. F. DUMMER, AT CORONADO BEACH, CAL.

Pond & Pond, Architects, Chicago, Ill.

Selected Curly Redwood Wainscoting; Fireplace Hard Burned Variegated Brick.

For Plans and Exteriors, see Vol. I, Pages 170 & 186

When a filament, as treated in the ordinary manner, is run at a high temperature in a lamp there is no improvement of the filament, but it was discovered that, if the treated filaments were subjected to the extremely high temperature of the electric resistance furnace - 3,000 to 3,700 degrees C. - at atmospheric pressure, the physical nature of the carbon was changed and the resulting filament could be operated at a higher temperature in the lamp and a higher efficiency.

Fig. 9. Typical Distribution Curves of Gem Lamp with Different Types of Reflectors.

Fig. 9. Typical Distribution Curves of Gem Lamp with Different Types of Reflectors.

and still maintain a life comparable to that of a 3.1-watt lamp. This special heating of the filament, which is applied to the base filament before it is flashed, as well as to the treated filament, causes the cold resistance of the carbon to be very materially decreased and the filament, as used in the lamp, has a positive temperature coefficient -rise in resistance with rise in temperature - a desirable feature from the standpoint of voltage regulation of the circuit from which the lamps are operated. The high temperature also results in the driving off of considerable of the material which, in the ordinary lamp, causes the globe to blacken after the lamp has been in use for some time.

The blackening of the bulb is responsible to a considerable degree for the decrease in candle-power of the incandescent lamp. The metallized filament lamp is operated at an efficiency of 2 5 watts per candle with a useful life of about 500 hours. The change in candle-power with change in voltage is less than in the ordinary lamp on account of the positive temperature coefficient of the filament. These lamps are not manufactured for very low candle-powers, owing to the difficulty of treating very slender filaments, but they are made in sizes consuming from 40 to 250 watts. Table II gives some useful information in connection with metallized filament lamps. The filaments are made in a variety of shapes and the distribution curves are usually modified in practice by the use of shades and reflectors. The general appearance of the lamp does not differ from that of the ordinary carbon lamp. Fig. 9 shows typical distribution curves of the metallized filament lamp as it is installed in practice. Metallic Filament Lamps. The Tantalum Lamp. The first of the metallic filament lamps to be introduced to any considerable extent commercially was the tantalum lamp. Dr. Bolton of the Siemens & Halske Company first discovered the methods of obtaining the pure metal tantalum. This metal is rendered ductile and drawn into slender filaments for incandescent lamps. Tantalum has a high tensile strength and high melting point, and tantalum filaments are operated at temperatures much higher than those used with the carbon filament lamp. On account of the comparatively low specific resistance of this material the filaments for 110-volt lamps must be long and slender, and this necessitates a special form of support. Figs. 10, 11, and 12 show some interesting views of the tantalum lamp and the filament. This lamp is operated at the efficiency of 2 watts per candle-power, with a life comparable to that of the ordinary lamp.

Fig. 10. Round Bulb Tantalum Lamp.

Fig. 10. Round Bulb Tantalum Lamp.

Fig. 11. Tantalum Filament Before and After 1,000 Hours' Use.

Fig. 11. Tantalum Filament Before and After 1,000 Hours' Use.

By special treatment it is possible to increase the resistance of the filaments so that they may be shorter and heavier than those used in the first of the tantalum lamps. It should be noted that the life of this type of lamp on alternating-current circuits is somewhat uncertain; it is much more satisfactory for operation on direct-current circuits. Tables III and lV give some general data on the tantalum lamp, and Figs. 13 and 14 show typical distribution curves for the units as installed at present.

Fig. 12. Appearance of Filament After Filament Frame Showing Having Been Used. Broken Filament.

Fig. 12. Appearance of Filament After Filament Frame Showing Having Been Used. Broken Filament.

Table III. Data On Tantalum Lamp

GENERAL ELECTRIC CO. MFTRS.

Size of Bulb

DIAMETER OF

BULB IN INCHES

Estimated Life

.Regular

Round

ON A. C.

On D. C.

40 watt

2 5/16

350

800

50 "

2 5/16

350

800

80 "

3 1/2

400

800

40 watt

3 3/4

350

800

80 "

5

400

800

table iv

Data on the Life of a 25C. P. Unit

No. of Hours Burned

Candle-P0WER

Watts per Candle

0

19.8

2.17

25

23. 6

1.865

50

23.1

1.90

125

22.3

1.98

225

22.4

1 .96

350

22 3

1 .97

450

22 .2

1.98

550

21.2

2.05

G50

19.6

2.20

Fig. 13. Vertical Distribution Curve Without Reflector.

Fig. 13. Vertical Distribution Curve Without Reflector.