Animal experimental work has suggested that ultraviolet radiation reduces dental caries incidence. The opportunity to complete a study on children in the 1-ppm water fluoridated community of Wetaskiwin, Alberta, Canada, through an experimental school design study, became possible between 1982 and 1984 as in winter children have to travel to and from school during hours of darkness. Two classrooms at the four primary schools in the city had full spectrum lighting introduced and the 102 children entering grade 5 spent 22 months of study in the same classrooms; 83 (81%) remained in the trial. Each child had DMFT, DMFS, including degree of caries involvement, gingivitis and oral hygiene indices recorded. Results showed that children receiving the full spectrum light had very low or no increase in caries incidence over the 22-month period compared with controls. DMFS findings, excluding ‘sticky fissures’ over the 22-month period, increased from 2.67 to 3.23 in the group receiving full spectrum light, compared with an increase of 2.32 to 4.46 in the control group (p < 0.001).