PREFACE 



The field of visible and near-visible light embraces a part of the 

 spectrum somewhat artificially separated from the radiations discussed in 

 the first two volumes of ''Radiation Biology," i.e., ultraviolet and high- 

 energy. Since the relation between the visible (and near-visible) and 

 ultraviolet parts of the spectrum is rather close, any separation ot the 

 two is arbitrary. This volume may be used as a separate work. But, 

 since treatment of material overlaps among the three volumes, more 

 benefit can be derived if all are read as a unit. Although rapid progress 

 in many aspects of photobiology has been made in the last three years, 

 i.e., after the manuscripts were completed, the basic information in this 

 book is of greatest importance. 



Special thanks belong to Dr. SterHng B. Hendricks, who carried great 

 responsibility in assembling the manuscripts for this volume. 



Alexander Hollaender 



