From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Results of life tests on 2.5-volt and 12-volt lamps for instrument lighting.
| Identifier | ExFiles\Box 168a\1\ img110 | |
| Date | 16th August 1938 | |
| 6089 6135 By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/RC.{R. Childs} By/RD. LAMPS FOR INSTRUMENT LIGHTING. Further tests, on instrument lighting lamps, have now been carried out. These consisted of running the lamps at their rated voltages until they burned out. A comparison was made between lamps rated at 2.5 volts, .2 ampere, and 12 volts 2.4 watts. Six 2.5 volt lamps were connected in parallel on a six-volt battery; each lamp having its own resistance to reduce the volts from 6 to 2.5, at which value it was maintained. Running under these conditions the lamps behaved as follows:- 1st lamp burned out at the end of 11 hrs 10 mins. 2nd " " " " " " " 13 " 40 " 3rd " " " " " " " 17 " 10 " 4th " " " " " " " 22 " 40 " 5th " " " " " " " 23 " 40 " 6th " has run for 50 hours, and is still all right. Two 12-volt lamps were connected in parallel, and the supply voltage maintained at 12.0 volts. These are still running; one having completed 200 hours, and the other 185 hours. These results confirm our earlier conclusion, that the average life, on normal voltage, of the smaller (2.5 and 3.5 volt) lamps, is very much shorter than that of the 12-volt type. To obtain from the smaller lamps a life approaching that of the 12-volt type, they would have to be under-run. This would result in a reduction of the total illumination, to regain which additional lamps and resistance units would have to be used. Thus the 2.5 volt lamp scheme would probably lose one of its advantages, i.e., low initial cost. In view of the above, we recommend that we go back to the 12-volt type of bulb for instrument lighting, the life of which is very much longer than either the 3½-volt or the 2½-volt type. Rm{William Robotham - Chief Engineer}/RC.{R. Childs} | ||