How Does Light Affect Goldfish?

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Goldfish need equal amounts of light and dark.

Goldfish are freshwater fish that can live an average of 12 to 20 years with the proper care. Lighting is an important part of goldfish health that must be constantly monitored. The reason is that goldfish are sensitive to sudden changes in light. Providing the proper amount of light and darkness will allow the fish to get the rest they need and prevent harmful algae from growing in the tank.


Direct sunlight can overheat the water in the fish tank, causing poor living conditions and bad health for the goldfish. Goldfish are cold water fish, so you must keep the water temperature between 65 and 75 degrees for optimum fish health. The wrong lighting in the fish tank can also lead to overheating. Fluorescent lighting is recommended for goldfish tanks because it heats the water less than incandescent lighting.


Goldfish have no eyelids, so the fish are unable to close their eyes and shield themselves from light at night to sleep. Goldfish must have 12 hours of light and 12 hours of darkness. Turn off the lights in your fish tank for 12 hours at night to help the goldfish get an adequate amount of sleep. Lights are available with timers to ensure goldfish are getting the right amount of light and darkness each day.



Lighting in goldfish tanks affects the pigment of the goldfish the same way it affects the pigment of human skin. Having the right lighting will help to ensure the goldfish's color develops to its full potential. Different lighting will make goldfish appear different shades of color. Good lighting will bring out the fish's natural color.

General Health

Too much direct sunlight will promote algae growth in the fish tank. This will create an unhealthy living environment for goldfish, leading to unhealthy fish and possibly loss of your goldfish. Since goldfish are sensitive to direct sunlight and sudden changes in light because they have no eyelids, putting a hood on your tank is a way to keep your goldfish safe from sudden changes in light.