## 4 Discussion
Phenylpropanol compounds, specifically verbascoside compound in _Verbena officinalis_, also were stimulated by blue and red light [84], by regulating the transcript levels of phenylpropanol biosynthetic genes [85; 86]. Finally, studies have revealed that green light added to blue and red light led to positive effects on phenolics, and generally bioactive phytochemicals accumulation in flower microgreen species [87]. Summarizing, the expected effect at the interaction of radiation in visible range (1.6-3.1 eV) with lifeless vegetal material, dried matter, or aqueous extracts, is of energy transfer to those compounds that contain either pi bonds, or atoms with non-bonding orbitals (meaning lone pair of oxygen, nitrogen and halogen atoms). The highest energy transfer will occur for the compounds which have maximum absorption peaks identical with the wavelength used for irradiation. Function of the laser power used, the sensitive compounds, containing double, conjugated bonds, matching with the wavelength used in the study will suffer small to moderate electronic delocalization, leading to so called activatory effects (likely measured as an increase in the antioxidant activity). Depending on the ratio of frequency/power used, at higher energy there can be obtained massive delocalization of electrons in the sensitive compounds, leading to reactive (oxygen) species generation, likely measured as a decrease of the antioxidant activity. Relative to the present study, antioxidant activity results suggest that excepting the wavelengths at 532 nm, and 660 nm, which indicated a clear pro-oxidant activity (evaluated as \(-14\%\) to \(-54\%\), respectively), all other wavelengths under study have resulted in an increase of antioxidant activity of the aqueous extracts of _P. lanccolata_; activatory effects were 785 nm/70 mW \(>488\) nm/40 mW \(>514\) nm/15 mW \(>552\) nm/15 mW. It must be reminded that all the experiments have been fulfilled in identical extraction conditions and technological parameters, therefore there are no other influences on the results apart from the laser wavelength and their powers. Regarding the most probably explanation of certain pro-oxidant effects observed at the irradiation of aqueous extracts from leaves of _P. lanccolata_ with laser at 660 nm, it must be noted that this wavelength is close to the maximum absorption peak of several phenolic acids frequently found in vegetable products. They are: cinnamic acid/666 nm; caffeic acid/670 nm; ferulic acid/672 nm; siringic acid/670 nm; gentisic acid/676 nm; gallic acid/684 nm and naringenin/676 nm. Caffeic acid and cinnamic acid are the main compounds in chlorogenic acid isomers and derivates such as phenylpropanol compounds, the most abundant phenolic species in _Plantago lanccolata_-derived products. Summarizing, the obtained results suggest that no valid conclusions can be drawn for both plant and animal raw materials, or even for plant materials only, as the response to irradiation with a certain wavelength depends on the specific content of the sensitive compounds, and the relationship between laser wavelength and power used. Figure 7: Light, the visible spectrum.