title: Biostimulatory windows in low-intensity laser activation: lasers, scanners, and NASA's light-emitting diode array system.
abstract: OBJECTIVE
  The purpose of this study was to assess and to formulate physically an irreducible set of irradiation parameters that could be relevant in the achieving reproducible light-induced effects in biological systems, both in vitro and in vivo.
  
  
  BACKGROUND
  Light-tissue interaction studies focusing on the evaluation of irradiation thresholds are basic for the extensively growing applications for medical lasers and related light-emitting systems. These thresholds are of central interest in the rejuvenation of collagens, photorefractive keratectomy, and wound healing.
  
  
  METHODS
  There is ample evidence that the action of light in biological systems depends at least on two threshold parameters: the energy density and the intensity. Depending on the particular light delivery system coupled to an irradiation source, the mean energy density and the local intensity have to be determined separately using adequate experimental methods.
  
  
  RESULTS
  From the observations of different research groups and our own observations, we conclude that the threshold parameters energy density and intensity are biologically independent from each other.
  
  
  CONCLUSIONS
  This independence is of practical importance, at least for the medical application of photobiological effects achieved at low-energy density levels, accounting for the success and the failure in most of the cold laser uses since Mester's pioneering work.
authors.affiliation: Central Institute of Biomedical Engineering, Department of Biomaterials, University of Ulm, Germany.
authors.forename: A P
authors.initials: AP
authors.lastname: Sommer
authors.forename: A L
authors.initials: AL
authors.lastname: Pinheiro
authors.forename: A R
authors.initials: AR
authors.lastname: Mester
authors.forename: R P
authors.initials: RP
authors.lastname: Franke
authors.forename: H T
authors.initials: HT
authors.lastname: Whelan
mesh_terms: D006801:Humans; D007834:Lasers