182 Introduction to the Study of Science 



for special studies and reports. The following summary may 

 serve as a guide in the examination of various kinds of lights 

 as to the points of practical importance. 



First. A thoroughly satisfactory artificial light should not 

 injure or endanger life or property. 



Second. It should be uniformly bright, steady, and so well 

 diffused as not to cause eyestrain, or undue contraction of the 

 pupil, both of which effects, if prolonged, will promote several 

 kinds of eye trouble. The light radiated through a frosted bulb 

 is diffused, that from a filament concentrated. Which light 

 produces less eyestrain? 



Third. A light should not throw out dangerous or dis- 

 agreeable gases, or rob the air of its oxygen in excessive measure. 

 Gaslight is regarded as unsatisfactory on this account. One 

 burner consumes about five times the amount of oxygen needed 

 by an average adult person. Carbon dioxid is produced in 

 correspondingly large amounts. If gas is incompletely burned, 

 its contamination of the air in a poorly ventilated room is in- 

 evitable, and special attention must be given to ventilation. 



Fourth. Artificial lighting appliances should be safe and 

 convenient for such handling as may be necessary. Movable 

 lights should be protected and reasonably safe. How are 

 electric lighting fixtures and appliances made safe for handling? 

 Are special lamps made for special conditions, as in mines where 

 gas or fire damp may occur ? 



Fifth. An artificial light, to be perfectly satisfactory, should 

 not radiate heat in considerable quantity. Heat radiation 

 means loss of light efficiency and discomfort in hot weather. 

 It increases danger to property from fire. The latest tungsten 

 lamp approaches the ideal of the firefly which gives light but 

 no heat. 



Sixth. A light should have such a quality as to blend com- 

 pletely all colors which it may contain, and allow no single color 

 to predominate, that is, for interior illumination of homes or 

 places where color is important, a white light is indispensable. 



