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Iodonium‐ and sulfonium‐type onium salts with counter anions of different nucleophilicities, namely [Al(O‐t‐C(CF3)4)4]−, [(CF3SO2)2N]−, SCN−, CF3‐SO3−, PF6−, and 3,5‐bis(methoxycarbonyl)benzenesulfonate, were investigated in both NIR and UV‐LED sensitized photoinitiated polymerizations at 790 nm and 395 nm wavelength exposures, respectively. The reactivity of the neutral sensitizer Sens1, and the cationic sensitizer Sens2 were examined in combination with the onium salts. The reaction rate was compared with isopropylthioxanthone (Sens3) as sensitizer. The reactivity of the initiating system is proposed to be associated with the conductivity of the salts in acrylate monomers such as tri(propylene glycol) (TPGDA), trimethylol propane triacrylate (TMPTA), and 1,6‐hexane diol diacrylate (HDDA). Salts carrying the [Al(O‐t‐C(CF3)4)4]− anion require new consideration of previously introduced models because the reactivity of the salts does not directly correlate with their conductivities. Rhodamine B lactone quantitatively probed formation of acidic cations between considering the reaction between [(t‐C4H9‐Ph)2I]+[Al(O‐t‐C(CF3)4)4]− and photoexcited Sens2 comprising either BF4−, PF6− or [Al(O‐t‐C(CF3)4)4]−. No significant differences were observed in terms of the reactivity. [ABSTRACT FROM AUTHOR]