## 4 Discussion  
To our knowledge, this study was the first to analyse changes in light irradiance caused by increasing distance in different exposure modes. The standard soft start and pulse modes, which many lamp manufacturers widely use, were tested [40,41]. Monowave LED-LCUs were selected for the study because, in our clinic, only composites with camphorquinone are used, which polymerises better in this type of light [24,42]. A Bluephase Meter II radiometer (Ivocalr Vivadent, Opfikon, Switzerland) was used to measure the lamp power. Although it does not match the accuracy of laboratory instruments, it has undoubted advantages [43]. It is easily accessible and enables quick and simple measurement of irradiance power. Previous research has shown great usefulness of this radiometer [28,44]; according to the manufacturer, it can measure the radiant power output from 380-550 nm with an accuracy of \(\pm\)10% [45]. However, several studies have been found in the literature showing the limitations of this measuring device [28,37]. Evaluation of the lamp irradiance with an increasing distance from 0 to 8 mm seems clinically useful. When restoring anterior teeth, the dentist can bring the LED LCU close to the composite surface, but in posterior teeth, the difficulty is the depth of the cavity and the height of the matrix band. The literature shows that increasing the distance to 10 mm or more results in insufficient superficial polymerisation or even no polymerisation [46,47]. Many publications indicate a distance of 4 mm as critical for the quality of polymerisation [48,49]. Our study showed statistically significant differences in light irradiance between values 0 and 2 mm versus 6 and 8, which may correspond to the studies of other researchers [49,50]. The light irradiance values at distances 0 and 2 were around 1000 mW/cm\({}^{2}\), which many researchers consider optimal for polymerisation in clinical conditions [48]. An increase in the distance to 4 mm resulted in an estimated decrease in intensity of 100-150 mW/cm\({}^{2}\). Previous studies have shown a regularity of 20% loss of lamp output with each 1 mm distance [37]. The range and light output of the lamp seem to be more stable now. Our results indicate an estimated loss of approximately 10% of light power/intensity with each 2 mm added distance. Also, [PERSON] et al. revealed the high sensitivity of the LED LCU to increasing distance. Their research showed the advantages of the halogen lamp over the LED lamp [49]. The explanation for this phenomenon may be the high thermal energy generated by halogen lamps, which has a positive effect on the polymerisation process. Researchers also indicate that of the many factors influencing the polymerisation process of the composite, the lamp intensity is the most crucial. Interestingly, according to some authors, it turns out to be much more important than layer thickness and exposure time [51]. It is also known that incomplete polymerisation results in the increased release of monomers and degradation products, as excellently demonstrated by [PERSON] et al. in their study. It has been shown that even at 4 mm, the amount of monomer released is significant [52]. This confirms the observations from our experiment that 4 mm is a somewhat critical distance. Increasing the distance of the LCU LED from the measuring device showed interesting differences between the tested modes. The most significant power loss was observed in the soft start mode. It seems that the potential advantages of this mode may be offset by its low resistance to distance increases. It's worth remembering that the rationale behind the effects of soft start and pulse modes is that using low irradiance in the first phase of curing slows the rate of resin polymerisation. As a result, this may allow polymer chains to slide on each other and prolong the pre-gel stage, yielding low polymerisation contraction stress and good marginal adaptation.