There are a few basic important factors you need to consider when choosing the camera lights, namely the amount of light and its color.
It is generally more difficult to shoot in low light, however, it can also be useful for some creative effects. Therefore, the power of your underwater light needs to be adjustable to suit the shooting conditions. For example, while the low power external strobe will usually be enough for macro photography, wide-angle shots require a broader and more powerful coverage.
The color of the light depends on the type of torch you choose (Halogen, LED or HID). Nowadays, Halogen lights are rarely used by underwater photographers as they produce a warm yellow glow. Strobes and LED lights are the best to use because they emit a cool white beam similar to daylight. This beam is capable of cutting through the blue (in warm saltwater) or green (in freshwater) to restore true color.
Finally, while underwater photography with one strobe is possible, it is recommended to use two strobes positioned on either side of the camera. This will allow you to produce more vibrant colors, eliminate harsh shadows, and establish creative lighting. Using two strobes also gives you more options and more control over lighting angles.