Everyone comes across a problem when he is choosing the lamps for a new house. This very much comes down to personal preference. Personally I prefer to use more than what is required, and then divide them into different switches. This will create different lighting effects. For example if you are putting the downlights into a kitchen you could have the downlights that are placed over the worktops on one switch and the other downlights that are illuminating the rest of the kitchen on another switch possibly a dimmer. This means that you have good task lighting where needed and controllable mood lighting elsewhere.
However there are still some important factors to consider.
If you don’t have any technical specifications about your special room, try using the following "Rule of Thumb". This best describes a kitchen, and can be adjusted for any room in your house.
Firstly make sure the downlights that are going to be close to your walls are not more than 600 mm into the room. The reason for this is that 600 mm is the standard measurement for the depth of your floor cupboards. This will mean that once the downlights are fitted, no shadows will be created over the area that you are working.
Secondly, you should now work out the position of the other lights by spacing them at intervals of between 900 mm and 1200 mm. From these figures you should now be able to calculate how many fitting will be in a row and how many rows you will need.
For more knowledge about downlights, pls visit: http://www.ledpanel-light.com/productstype/led-downlight.htm