title: Wavelength, frequency, and color: absolute or relative concepts?
abstract: OBJECTIVE
  The purpose of the present study is to call attention to well-established concepts in optics, which, however, are not necessarily known by medical laser users but may be important for interpretation of some data.
  
  
  BACKGROUND
  In reviewing some aspects of the physical concepts of wavelength, frequency, photon energy, and color, it was possible to establish, beyond doubt, the right conditions to use these terms to classify specific laser radiations. This may help in the correct interpretation of some low-level laser therapy (LLLT) experimental results.
  
  
  METHODS
  In order to achieve our objective--maintaining the reader's interest--we use the simplest physical concepts and equations necessary for nonphysicists to understand this subject.
  
  
  RESULTS
  The most important result pointed out through this study is the fact that the numerical value for wavelength, normally assigned to commercial lasers, should not be used to describe the light propagation inside the tissue.
  
  
  CONCLUSIONS
  The knowledge of the relation among the magnitudes discussed in the present study and their effects, although it does not add much to the use of a laser merely as a cutting instrument, becomes of fundamental significance when used to determine the effects that depend on light propagation within biological tissue and that do not result only from absorption of light energy. This will certainly help in the understanding of phenomena whose causes are attributed to the electric and magnetic polarization of laser radiation, as seems to be the case observed in laser biostimulation.
authors.affiliation: Department of Ophthalmo-otorhinolaryngology, and Center for Experimental Medicine and Surgery (NMCE), School of Medical Sciences (FCM), State University of Campinas, Campinas, SP, Brazil. jhnicola@fcm.unicamp.br
authors.forename: Jorge H
authors.initials: JH
authors.lastname: Nicola
authors.forename: Ester M D
authors.initials: EM
authors.lastname: Nicola
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D003116:Color; D006801:Humans; D007834:Lasers; D008433:Mathematics; D011827:Radiation; D012031:Refractometry