7 



Reprinted from The American Journal of Physiology, Vol. 44, No. 4 

 November, 1917 



STUDIES ON THE RELATIVE PHYSIOLOGICAL VALUE OF 

 SPECTRAL LIGHTS 



I. Apparatus 



HENRY LAURENS and HENRY D. HOOKER, Jr. 



From the Osborn Memorial Laboratories, Yale University 



Received for publication September 1, 1917 

 INTRODUCTION 



The present paper is concerned primarily with a description of an 

 apparatus by means of which spectral lights of equal radiant energy 

 content can be obtained and comparative work of wide range carried 

 out. Before proceeding to a description of this apparatus it seems 

 best to point out, as briefly as possible, why such an apparatus is 

 essential. 



Against much of the work that has been done on the study of the 

 relative physiological value of spectral lights the objection can be 

 raised that sufficiently accurate m.ethods of experimentation and de- 

 scription have not been employed. Speaking more particularly of the 

 work which has been done on the "color vision" of animals other 

 than m.an, and excluding the early investigations in which colored light 

 was obtained by means of filters, screens, etc., much inaccuracy is 

 found in those in which spectral light is used. By observing the in- 

 fluence of an entire dispersion spectrum on the aggregation of organisms 

 results are obtained which leave much to be desired quantitatively. 

 Also, in much of the work indefinite and inadequate terms of descrip- 

 tion are used, in that, e.g., one light is said to be brighter than another, 

 as measured by the human eye, or equally bright, etc. This mode of 

 description is purely subjective. Only qualitative facts are learned 

 when a spectrum, is viewed as a whole and this method does not enable 

 us to say by how much one light is brighter than another, brightness 

 being a quajititative conception only when measured photometrically. 



It is therefore not permissible to compare the ''color vision" of an 

 organism to that of the normal human eye or of the color blind eye 



504 



