As mentioned before, Underwater Photography is not for the average photographer. The skills and equipments for such activities are demanding and exact. You cannot use the normal photographic equipments for underwater photography. Even if you do, special enclosures must be used to prevent seawater from coming into contact with them. Seawater is highly corrosive and will eventually damage any equipment that is not designed to withstand its effects.
To make matters worse, underwater lighting conditions tends to be dimmer. Additionally, because of the higher density of particles, they tend to give volumetric effects as well.
To add to the challenge, you will need to be able to handle whatever lighting equipments that you are using and at the same time maneuvers skillfully within the watery environment. Therefore, if you intend to take underwater photos, you will need specially designed lighting equipments such as Photofocus lights.
Underwater lighting equipments are not easy to find too. Because of that, sometimes a more cost effective way is to buy them online.
One of the more established site that deals with Underwater Lighting and Photographic equipment is Nocturnal Light.
Nocturnal Lights Inc itself is an established manufacturer of underwater lighting systems. Basically, Nocturnal Light carries 3 main categories of equipments: Dive Light, Photofocus Light and Video Lights. The photo below shows one of their Photofocus light products.
All their products are built for demanding underwater conditions. This include producing them only with aircraft grade Aluminium. Additionally, over-charged battery powering technology are utilised to ensure the best light output
The main buyers of their products are underwater photographers, underwater videographers and scuba divers.