when fluorescent lights flicker it's either the globe or the starter that needs replacing. And they should both be replaced together anyway.
eg: you replace the globe because it no longer works, and you replace the starter at the same time.
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You can go to any hardware store or lighting shop and have a look at LED lights. They have strip lights and led spotlights. The spotlights penetrate deeper water more effectively. If you have a tall tank then spotlights are a better option.
The LED lights come in a range of wattages and kelvin ratings and lumens. Generally higher wattage means more power used but more light is produced at the same time.
More lumens means more intensity/ light.
Kelvin rating is the temperature of the globe. Natural sunlight has a Kelvin rating around 5700K. Try to get a light with a Kelvin rating around 6500K as the main light, and if you want a morning/ evening light get one with a 2500-3000K rating.
The higher rating (6500k) is often referred to as a cool light, whereas the lower rating (2500K) is referred to as a warm light. The cool light has a white glow, the warm light has a yellow/ orange tinge.
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How tall is the tank and do you have plants in it? If you want live plants then you want higher wattage and more lumens.