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Safety Lamps
Light. – The value of a safety-lamp depends to a great extent on the amount of light it will give, because a good light conduces to the safety, comfort, and earning power of the workmen. Dr. Court, of Staveley, has found that miners using safety-lamps suffer from a disease of the eyes called nystagmus, whereas those using candles do not suffer from it. The writer has made a number of observations to ascertain the amount of light given by various lamps. It must, however, be borne in mind that the light of a lamp varies greatly with the nature of the oil used, and the state of the wick, the cleanness of the glass and gauze, and the height of the flame. The illumination given by a candle is, from a collier’s point of view, very satisfactory. There is seldom a strong current in the working place, so that the candle does not unduly sweal. The light given by a safety-lamp is only on a certain plane, a shade being thrown by the top and bottom, and pillars supporting the top; so that a lamp which, according to a photometric measurement made opposite the flame, gives a light equal to one-third of a candle, may in practical use only give the light of one-tenth of a candle, and it is probable that in many cases the light of a good candle is equal to thirty Davy lamps in ordinary condition with ordinary oil.
Swan’s portable electric lamp gives a better all-round light than an oil-lamp, and is equal to about one-third of a candle on that side of the lamp where the light is fixed.
The following table shows the results of a number of photometric tests made by the author with safety-lamps :-
| Name of safety-lamp | Number of lamps required to equal one standard sperm candle, the illuminated object being on a level with the flame | Number of lamps required to equal one standard sperm candle, allowing for the shade cast by lamp cover, bottom, and pillars. The candle and the lamp being each in a cyclinder of white tracing paper 2 ft. high and 8 in. diameter |
|---|---|---|
| Davy lamp, very large flame | 7 | 19 |
| Davy lamp, moderate flame | 18 | 27 |
| Davy lamp, moderate flame | 15 | 32 |
| Davy lamp, in tin can, good flame | 9 | – |
| Davy lamp, in tin can, flame rather low | 25 | – |
| Protector, shielded Marsaut, good flame | 3 | – |
| Protector, shielded Marsaut, flame average height | 4¼ | – |
| Clifford, very good flame | 1.9 | – |
| Clifford, moderate flame | 2½ | 5 |
| Deflector, large flat flame | 3 | – |
| Deflector, moderate clear flame | 5 | – |
| Deflector, small moderate flame | 6 | – |
| Thorneburry, good flame | 1¾ | 5 |
| Ashworth, new pattern | 3½ | 11½ |
| Stephenson, good flame | 7½ | 23 |
| Tallow candle, good average flame | 1¾ | – |
| Tallow candle, large blaze | 0.8 | – |
The following table gives the weights of various lamps without oil or wick :-
| Name of lamp | lbs. | ozs. |
|---|---|---|
| Davy | 1 | 10 |
| Pieler | 1 | 14 |
| Stephenson | 2 | 0 |
| Tin-can Davy | 2 | 4 |
| Shielded Muesler with reflector | 2 | 14½ |
| Howat | 2 | 15 |
| Purdy's | 3 | 0 |
| Morgan | 3 | 0 |
| Clifford | 3 | 4 |
| Protector | 3 | 4 |
| Marsaut | 3 | 4½ |
| Clanny, with corrugated shield | 3 | 5 |
| Deflector | 3 | 7 |
| Thorneburry | 4 | 2 |
| Swan portable electric, charged (not made now) | 6 | 0 |
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