HEADLAMP construction is presented in summarized form, twelve needful factors being stated by the authors. Accelerated mechanical tests, which are designed to give within a few days results of what may be expected to take place after several years of road service, are conducted in the Headlight Laboratory of the University of California. These are described and illustrated under the headings: Vibration, durability, moisture, dust and electrical insulation, and the results are stated. A few correlation tests are commented upon. Headlamp vibration is treated at length, together with an analysis of headlamp vibration-characteristics, and a differentiation is made between vibration due to the engine and that due to roadway shocks.
Measurement of headlight glare upon the roadway was made by obtaining continuous records of the illumination of the driver's eye from opposing cars or other equipment, the apparatus used including a photoelectric cell mounted inside the windshield in a direct line with the driver's eyes, an amplifier specially designed to cover the range of illumination and an oscillograph for obtaining a photographic record. Partial results of these tests are given. The general conclusions reached are set forth in six divisions, the last being that 0.07 ft-candle at 100 ft. is indicated as a criterion of glare.