Good deck lighting can present quite a challenge to the homeowner; it requires a perfect blend of practical and beautiful. Decks are used primarily as extensions of the living space, and as such they must mimic the same characteristics of the home by offering ambience but also sufficient light for tasks.
The best way to achieve this is by using combination lighting. Certain areas, such as the cooking area (if there is one), or a reading area, must have enough lighting that you can see what you are doing without eye strain or requiring a secondary light source. But other areas require only the barest hint of light, enough to accentuate the lines of the deck, but not so much that it detracts from the atmosphere.
Fortunately for homeowner there are many many choices when it comes to deck lights. Practical consideration must be given to things like stairs and railings, for safety concerns but also since they give the deck its definition. Downlighting is often a good choice for these, so that the light does not shine into your eyes but rather illuminates the stairs themselves, or the railing.
Spot lights can be used on a deck to light up particular objects, such as artwork, furniture, plants, or even a particular place from where light is reflected out and creates an atmospheric effect. The narrower the spot light, the more dramatic the effect, but also the more other light sources may be required to provide sufficient light.
Flood lights are rarely used on decks, since they are simply a 'wash' of light and not much good at creating drama. However, for security and task lighting, they can be quite effective. Often the best choice is to have mood lighting and task lighting on seperate switches and even circuits, so that a choice can be made depending on what is required.
When decking lights are very bright, the light source itself should be shielded or hidden so that you are not blinded by the light. Spot lights are often recessed, and sometimes the light is hidden behind something, so that the source is not seen.
Softer lighting does not have this requirement. In fact, often the idea is to actually see the light fixture itself, since these are a thing of beauty. This kind of lighting is often low-voltage, since there is less need for power and more simply for ambience.
Whatever choices you make for your deck lighting project, just remember to balance the practical with the ambient, and try several different types of light. Also remember the less is more rule; there is such a thing as too much light when you are trying to establish an atmosphere. And decking lights are no different than interior lights when it comes to this.