Halide Lights Why Do The Metal Halide Lights Usually Come With Actinic Light?What Purpose Dose The Actinic Light Have?

Why do the metal halide lights usually come with actinic light?What purpose dose the actinic light have? - halide lights

I believe a aqurium Reef Marine Light is vital. Metal halide lighting to simulate sunlight? If so, why do I have actinic light as well? Need help.
Thank you in advance.
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