622 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
of surfaces is a prominent feature of the most recent advance in the 
science of illumination. Glare both from light source and from 
reflecting surfaces is largely a question of contrast, and its suppression 
in order to promote ocular welfare is one of the principal aims of the 
lighting practitioner to-day.1 Excessive brightness means excessive 
contrast with surrounding objects.?, Sometimes a light source, which 
is so bright as to occasion discomfort amid dark surroundings, 
becomes innocuous when amid bright surroundings. The general 
recognition of the need for contrast limitation has been effective in 
reducing contrast in the more recent installations.’ 
Glare is intimately connected with diffusion of ight. It is a sub- 
ject to which a great deal of study has been given within the last few 
years. In a paper before this institute Sweet presented the results of 
some laboratory experiments on the effect of glare due to the presence 
of a light source within the field of vision. While the conditions 
which he employed were extreme and the effect was exaggerated 
beyond that met in practice, yet the consequences experienced in 
ordinary installations differ from those found in his experiments only 
in degree. Glare due to exposed light sources means diminished 
seeing ability, discomfort, and possible injury to the eyes. Another 
effect also known as glare is that attending specular reflection from 
polished surfaces. This is a subject which has received especial atten- 
tion during recent years. Glare of this kind is again a matter of 
excessive contrast. One views the imperfectly reflected image of a 
light source upon the page of a book, brightness of the image being far 
in excess of the immediate surroundings and the general surround- 
ings. The same means which are effective in reducing contrasts 
between the light source and its surroundings are naturally effective 
in reducing the contrast between the reflected image of the light 
source and its surroundings. Thus in avoiding glare due to exposed 
light sources, glare due to specular reflection is ikewise avoided.* 
The engineering aspects, together with those aspects which pertain 
to vision, in large part constitute the science of illumination. Es- 
1 Methods of perception: “‘Some physiological factors in illumination and photometry;” Bell; Trans. Illg. 
Eng. Soc., June, 1906, p.3. Allowableamplitudes and frequencies of voltage fluctuations in incandescent 
lamp work;” Ives; Trans. Illg. Eng. Soc., 1909, p. 709. ‘‘ Physiological points bearing on glare;’’ Cobb; 
Trans. Tllg. Eng. Soc., 1911, p. 153. ‘Notes on spectral character of light upon the effectiveness of vision;”’ 
Luckiesch; Trans. Illg. Eng. Soc., 1912, p. 135. 
2 Brightness: ‘‘Intrinsie brightness of lighting sources;”? Woodwell; Trans. Illg. Eng. Soc., 1908, p. 573. 
“The measurement of brightness and its significance;” Ives; Trans. Illg. Eng. Soc., vol. 9, No. 3. 
3 Light absorption and reflection coefficients: ‘‘Coefficients of diffuse reflection;”’ Bell; Trans. Illg. Eng. 
Soc., 1907, p. 653. ‘‘Some experiments on reflection from ceilings, walls, and floor;”” Lansingh and Rolph. 
Trans. Illg. Eng. Soc., 1908, p. 584. “‘ Effect of the variation of the incident angle on the coefficient of diffuse 
reflection;” Gilpin; Trans. Illg. Eng. Soc., 1910, p. 854. ‘‘Reflection coefficients; Bauder; Trans. Ilg. 
Eng. Soc., 1911, p. 85. “Some reflecting properties of painted interior walls;” Jordan; Trans. Ilg. Eng. 
Soc., 1912, p. 529. 
4 Contrast, glare, etc.: ‘Physiological points bearing on glare;’”? Cobb; Trans. Tllg. Eng. Soc., 1911, p. 153, 
“ Artificial illumination as a factor in the production of ocular discomfort;’’ Black; Trans. Illg. Eng. Soc., 
1911, p.166. “The effectiveness of light as influenced by systems and surroundings;” Cravath; Trans. Illg. 
Eng. Soc., 1911, p. 782. 
