Lighting is one of the most important components of a reef aquarium. Correct color with the appropriate intensity is a critical factor in the health of aquarium organisms. A combination of LED Blue Actinic, creating 18,000-degree K to 20,000-degree K are what many aquarium hobbyists consider the most pleasing, not only for the tank inhabitants, but also for viewing pleasures. Using this light in conjunction with your existing white lighting, will help bring your Kelvin spectrum in between this appropriate range.
Actinic is blue... more precisely Actinic is the FAR blue range
The first line in WIKIPEDIA
"Actinic light is either light that affects photographic film, or will facilitate photosynthesis or stimulate light sensitive species
A wavelength of approximately 410 to 465 nanometers (nm), are the wavelengths where photosynthetic efficiency in relation to corals is at its highest.
Design specifications subject to slightly change as new technologies are developed.