by Tom Sarac

The visible light spectrum is composed of a number of colors, and they are not all equally important for the life we keep in our aquariums that photosynthesize.

Our human eyes respond best to the green spectrum, the one that is least implicated in photosynthesis. However, the blue spectrum is arguably the most important part of the light spectrum for both planted freshwater and marine reef aquariums.

The blue (including violet) spectrum spans from approximately 380nm to 490nm, which represents the beginning of the visible light range of wavelengths within electromagnetic spectrum. These shorter waves of light contain the most energy within the visible light spectrum, making them very important in terms of light energy that fuels and drives photosynthesis.

In fact, as the days start to get longer, the amount of blue light that reaches the earth’s surface increases and drives plant growth, ultimately stimulating plants to become bushier and reach a denser vegetative state. Furthermore, most types of chlorophyll use the blue spectrum more efficiently versus the also important red spectrum. This is logical given the higher energy levels of blue light photons.

When considering photosynthetic corals and their action spectra, photosynthesis blue light is where it’s at. Given that blue light with its higher energy levels reaches down farther into ocean water, corals have evolved to use the blue spectrum most efficiently as well. In fact, blue light makes it down to over 300 feet in depth, whereas green doesn’t even make it to 100 feet.

So next time you’re gazing at your amazing marine reef aquarium and admiring how beautifully the blues are popping from some of your marine fish, or how intensely some corals are fluorescing, remember you owe that to the short wave lengths of visible light.