The lighting of the aquarium is not an unimportant factor. From the right lighting depends on the normal activity of the inhabitants of your aquarium and how they will look. There are reflectors (lighting devices for lighting aquariums) that allow you to light the aquarium from above or from the side.
In the past, incandescent lamps were mainly used in such devices. This allowed not only to illuminate the aquarium, but also to heat it due to the large heat generated by the incandescent lamps. Especially well heated aquarium at the lateral location of the reflector. It would seem that this is good – one shot killed two birds and lighted and heated. But it is not quite so.
With this method of lighting it was difficult to monitor the temperature of the water, which could quickly overheat when the reflector was on, especially in summer. And at night when the lighting was not necessary, the water in the aquarium quickly cooled. In addition, the invariably yellowish tint inherent in incandescent light distorts the natural coloring of fish.
Technology does not stand still and aquarium technology is no different. Wasteful incandescent lamps have been replaced by low-pressure mercury lamps. They practically do not heat up, can have different shades of glow, consume much less energy. All this allows you to illuminate the aquarium in such a way as to most favorably represent its inhabitants. Due to the low heat emission, you can illuminate the aquarium with several light sources without fear of boiling the water with its inhabitants.
As already mentioned for the most favorable observation of the underwater kingdom it is important how it is illuminated. Fish look best in reflected light. That is, when the light source directed at the fish is in the same side as the observer. But it is quite difficult to realize technically. Do not arrange a spotlight on the opposite wall of the aquarium …
This is partly solved by placing the lighting device on the side of the aquarium. But this is not physiological for the fish. In nature, the light into the water body always comes from above. So illuminate ninety percent of modern aquariums. And beginner aquarist makes sense to illuminate your aquarium from above. This is both easier and physiological for all the inhabitants of your indoor pond.
And do not try to put a small sun in the reflector. Lighting should be sufficient for comfortable observation of the inhabitants of the underwater kingdom, but should not cause discomfort to these same inhabitants because of excessive brightness. Also do not arrange in the aquarium all sorts of illuminations. Fish are living creatures, and your aquarium is their home. It should be cozy to those creatures responsibility for which you have taken on.