To see anything in deep water, additional source of the light is necessary. Here you have a description of the popular types of lamps.

Halogen lamps

Cheap and bright. Easily available in any Home&Garden shop. 50W/12V halogen lamp costs about 1€. The only problem is power consumption. For 50W/12V lamp you must supply 4A. The way you can limit power consumption is to use PWM, this gives you the possibility to limit the brightness and power according to your current needs.