This is an ad from the April 1917 edition of Hugo Gernsback’s The Electrical Experimenter, which you can read on archive.org here.
I can only assume this is an early blacklight bulb (operates on battery or alternating or direct current) that is supposed to infuse your blood with ozone (how?) lending vitality to your scalp, face, and body (how?).
It’s under an ad for an electric water heater and next to an article about sunlight’s effect on magnetic needles based on a discussion by “F. C. Loring, department of terrestrial magnetism, Carnegie Institution.” I guess this was an early study of what we now call solar radiation.
No mention of violet light, though.