There are times when there just isn't enough available light to get a successful picture, such as the subject hidden under an overhang, taking pictures on a night dive or in murky UK waters. So underwater photographers use extra lighting in the form of strobes. This is just a name for a flashgun used underwater, it can mean the little flash built into your camera or external strobes that are more powerful and cover a wider angle. Your built in flash is often discounted out of hand by lots of underwater photographers, but as long as you use it within its limitations it can still be very useful. It is best used for very close-up or macro subjects, anything further away than about a foot, and it is not going to work very well. This is because it's low power doesn't have the range to penetrate a lot of water. Though much more of a reason to stay close is because even in good visibility there are many unseen tiny particles in the water which will be illuminated and show up as out of focus blobs, obscuring and lowering the quality of your shots. This is commonly called "backscatter" and to help avoid it we need to use an external strobe. Using an external strobe gives a much greater degree of flexibility. We can successfully illuminate subjects that are both larger and a bit further away than if we had used the built in flash. More importantly though we can help with the backscatter problem because the flash is positioned further away from the axis of the camera's lens, this reduces the chance of the tiny particles reflecting back into the camera's lens. More artistic lighting possibilities are now opened up to you, because you have a range of positions you can place the strobe at, most off camera strobes are mounted on flexible arms. Pointing the strobe acutely to the side of the subject, will result in strong shadows on one side of the picture, adding drama or depth to a shot. Or you could experiment with top or up lighting, for different effects. We have also started using dive torches instead of a strobe to provide an alternative source of illumination. You will of course need some way of mounting it to your camera. As long as the light is reasonably powerful, it is a great way to shoot macro on a night dive. You will need to carry out a white balance reading but you will only have to do this once at the beginning of the dive. As it is a continuous light source, it is a great way to judge what the outcome of the shot is going to be, so positioning the light is a very easy. We prefer one of the more powerful LED or HID torches as they seem to provide more consistent and diffuse lighting. Using an alternate light source gives you the flexibility to cover most picture taking scenarios, but shouldn't always be considered your primary light source. We have numerous different options for lighting our subjects available to us nowadays, don't be scared to experiment. Use a torch and manual white balance, move your strobe around to achieve different lighting effects, what have you got to lose, certainly not film.