When choosing a dive light it is important to consider your dive needs and environmental factors to choose the proper light. Dive torches come in different sizes, styles and price tags. Every type of light is designed for particular use in mind.
Primary dive lights can be sometimes used during the deeper daytime dives, but are an absolute necessity for a night or a wreck dive. They are normally larger and brighter than all the other types of lights and come in either pistol or lantern grip. You can also choose between a Halogen (Xenon), LED and HID versions. Halogen lights are the least expensive and have a soft yellow glow, LED torches put out a while beam and usually have a longer life, while HID lights are the preferred option among professional divers and underwater photographers, as they are the brightest. Another major point to consider with regards to primary dive lights is power capacity. Here more power is always better since the light is meant to be kept on all of the time during the night dive.
The secondary dive light is also an important accessory meant to protect you in case your primary dive light fails during the night dive. Remember, it is a matter of your safety to always carry a back-up torch when going diving after the dark. As for the construction, secondary lights are typically more compact and lightweight, so you can store them in your BC pocket. They also put out a narrower beam, which makes them perfect for exploring under ledges or the cracks and crevices of a reef.
Lastly, there are special lights for underwater photography or videography. They help to adequately light your subjects and capture the vibrant colors of marine flora and fauna. The bright wide beam is perfect for wide-angle cameras and general photography and video use.