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I have included on this page what most people would consider a flashlight, but also any light that uses the No. Also some fixed battery powered lights like used on barricades or in purses, &etc. And some closley related patents like anti reflection coatings or earlier lights.
Not on the page are patents related to Flashlights as used on cameras.
For example the GE 223 life might be described as: Life = 2157200 / (V^16), so when V=2.25 Volts Life = 5 hr BUT at 3.0 Volts Life = 3 Minutes!
One factor that may have allowed a longer bulb life in the old falsh lights is the internal resistance of the battery and flash light.
Light ~ V^3.4 Power ~ V^1.6 Life ~ 1/V^16 Color ~ V^0.42 Because of the boiling temperature of tungsten the best possible efficiency is about 52 lumens/watt.
Military Survival Lights web page M-227 Signal Lamp Background Components Lamps Lamp Test E10 Repairing Loose Bulbs Photos at 2X life size 1915 Catalog listing of Lamps Table of Newer Lamps Edison 10 mm Miniature Screw Lamp Base (E10) Batteries Cylindrical Prismatic Size Table No. 1653 Electric Candle Table Lights Electric Storage Battery Co. Once the dry cell battery became available flashlights became more popular than they were when a lead acid or other wet battery was needed.When the voltage gets to 3.7 the current starts to decrease with time, like the resistance is going up with time which might happen is the filament is starting to boil away.Although given for currents close to the rated current these relationships give a feel for how incandescent lamps work.Those numbers are "nicer" than the metric equivalent 1.75mm pitch and 8.82 mm pitch diameter. I'm guessing the 10 mm came from the fact that these lamps were being made and sold in many countries, not just the U. Even today there are flashlight lamps that are fairly hard to come by.
But being able to use the flashlight is a large part of it's appeal. Note that a nominal lamp life is 15 hours at rated voltage.The early Flash Lights used an Edison type minature screw base lamp very much like the # 14.A problem with this lamp is that the filament location is not controlled.It's my feeling he was correct, running the Pocket Flash Lights on a full 3.0 volts from a modern battery that's "stiff" will greatly shorten the life, if not just burn it out.\ This is a test stand I built to allow measuring the Voltage and Current of E10 based lamps. 6 Dry Cell battery adapter and the wire is from the Hubbard spool which is 16 AWG solid copper, much larger than needed to light the bulb, but good for measuring the resistance of cold lamps.