How to calculate lighting needs

Written by g.k. bayne
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Calculating the illumination for a room or an entire home is based upon a standard rating. This is typically performed by an electrician when they wire a home or a room addition. The purpose for this base calculation is to provide enough electrical power to each room and in the main circuit panel for the home's occupants' lighting needs. Once the home or room is finished, additional considerations must be employed. These concerns fall into the colour of the room, the room's use and, of course, the placement of the lighting fixtures. The amount of light may be a personal preference, but, as we grow older, our lighting requirements may increase. Theses factors should be taken into consideration for future expansion of illumination.

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  1. 1

    Begin by calculating the basic lighting load according to the National Electrical Code for dwelling units. The table 220-3(b) indicates that a load factor of three (volt-amperes) also called watts, be allotted for in the main electrical system. Translate this into the home's interior of 1,500 square feet. The total wattage of lighting will be 4,500 for this size home.

  2. 2

    Find the required wattage for a room that is 10 feet wide by 15 feet long. The square footage is 150 feet with a wattage requirement of 450 watts. This can equal nine 60-watt light bulbs for this small room. This basic guideline only ensures that there is plenty of electrical power dedicated to the circuits that service this room. Some of the power can be provided by the receptacles of the room.

  3. 3

    Consider the use of the room when figuring light placement. A reading room may need more lights at specific places. A dining room may only require two or three properly centred lights over a main table for atmosphere and illumination. Kitchen areas may need spot lighting and specific cove lighting as cabinets could block certain light fixtures.

  4. 4

    Visualise the rooms colour and wall finishes. Lighter coloured rooms, especially ceilings and walls will reflect certain lighting. Dark floors can quickly absorb light from any type of overhead or ceiling fixtures.

  5. 5

    Make use of extension cords and movable light fixtures when planning lighting needs in a new room addition. Find a lighting decorator that can help you in making selections of various fixtures. Incorporate outdoor lighting as much as possible into a room through the use of large windows or skylights.

Tips and warnings

  • Utilise a light meter that shows the amount of light in lumens. This is a simple tool to operate and most have a corresponding chart to understand the readings. See the resource link.

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