NATURAL AND ARTIFICIAL LIGHTING 55 



70. Light Should Come from Above. Through ages of 

 out-of-door life the eye has become adapted to receiving light 

 from above. The human eye is not adapted to receiving 

 strong light from below or even from a source on a level with 

 the eye. By far the strongest light is received from the sun at 

 midday. But at that hour the sunlight comes from overhead, 

 and even its great intensity is not particularly painful. On 

 the other hand, we are all familiar with the blinding effect of 

 the far less intense rays of the setting sun. When boating, the 

 rays reflected from the water come from below the eye; the 

 effect is blinding and extremely unpleasant. Snow blindness 

 is common in the polar regions, and even uncivilized races 

 have invented devices to protect the eyes against the ill effects 

 of the sun's rays reflected from the snow. Even the reflected 

 light from concrete walks and from light-colored soils is very 

 trying to the eyes because it comes from below. 



71. Direct Light and Diffused Light. The most comfortable 

 light, and therefore the best, is DIFFUSED LIGHT from above. 



FIG. 39. Direct light reflected FIG. 40. Diffused light reflected 



from a polished surface. from a rough surface. 



When light comes directly from a luminous body it is said 

 to be DIRECT LIGHT; when such rays are reflected from a 

 smooth surface, such as a mirror or any highly polished surface, 

 they still have the properties of the direct rays. All such rays 

 are parallel to each other or nearly so (Fig. 39). All such 

 direct light, i.e., light with parallel rays, is unpleasant and more 

 or less injurious to the eye. Light is said to be diffused when 

 its rays are not parallel. 



