Below is a list of some of the things that need to be taken into account when planning your lighting design:

Purpose – The activities that are carried out in specific areas of the house will determine what sort of lighting should be implemented.
Size – The size of the room dictates how many fittings will be required (or how much daylight is required) to light the room sufficiently for the purposes it`s required for.
Positioning – Where lights are placed, whether they`re directional or diffuse, how they`re arranged and how they`re spaced all makes a difference to the light in your home.
Type – Different types of light globes perform very differently, and not all globes are ideal for all situations.
Surfaces – Walls, furniture, carpet, ceilings and mirrors all reflect light in different ways.
Decoration – Lighting is pivotal to the way objects and aspects of an area are emphasised and portrayed.
Efficiency – A carefully planned and efficient lighting system can save you a small fortune in the long run.

How much light?

Determining the correct light levels for a home environment is a very complicated subject and depends on a degree on the individuals perception and requirements. The formula below, however, can be used as a rule of thumb. Measure the room size in square metres and multiply this by 25 (for incandescent lamps) 15 (for halogen lamps) or 19 (if using compact fluorescent lamps). This will give you the total watts required to light the room.

Example 1:

a room 5m x 5m has an area of 25sq metres. If we are to use conventional incandescent lamps we multiply this by 25 giving a total wattage of 625 watts. This can be made up as required, for example as follows:
2x 75W table lamps = 150W
2x 3 light ceiling lights each with 40W bulbs = 240W
2x double wall lights each with 40W bulbs = 160W
2x single wall lights each with 40W bulbs = 80W
Total = 630W

Example 2:

a kitchen 3m x 6m = 18 square metres. If we intend to use low voltage halogen dichroic lamps then we multiply this by 15 to arrive at 270watts required in total. This can be made up as follows:
1x 3 light halogen bar fitting with adjustable heads each with 50W lamps = 150W
6x downlighters mounted in the ceiling each with 20 W dichroic lamps = 120W
Total = 270W

Please note that this formula is a guide only and some people prefer more light, others less. A useful measure is to over estimate by 10 - 15% and install a dimmer to give you more control. If in doubt seek professional advice.