It seems strange that there are bar-element spells for the 6 "main" elements, but not for light and dark. This is a hole in WHM, RDM and RUN elemental defensive options without there being an evident reason why. (For example, BRD get elemental defense songs (carols) in all 8 elements, and elemental enfeebling songs (threnody) in all 8 elements. SCH gets weather-effect spells for all 8 eleements. and RUN gets job ability-based runes in all 8 elements.)
I would suggest adding the WHM spells Barlightra and Bardarkra, and RDM and RUN spells Barlight and Bardark, with the same general mechanics as the existing other bar-element spells.