Light Wattage Help

[boabmac63]

I have lights in my tank but unsure of what they are i cant remember its a 64 litre tank with a bulb thing its not long that goes accros the top its just at 1 side but it does light up the whole tank i would like plants in my tank such as riccia amazon sword christmas moss java moss dwarfhair grass and moss balls what wattage of light would do please help also it has to slots one has a blue night light but i could Put another bright one in and just turn them off at night