Calculating lighting requirement for an office space can be done using quick and easy formulas or more complicated procedures. Calculations involve determining the amount of watts needed to light up a room. In addition, lighting professionals have recommended guidelines for the amount of light or lumens needed in a workspace for basic office and computer work. These guidelines can also be used to determine the proper amount of lighting needed.

Measure the length and width in feet of the given office and computer space using a tape measure. Calculate the square footage for the room by multiplying the length by the width. If the room is not square or rectangular, use a circular formula for obtaining the square footage. For example, the area of a circular room would be pi (3.14) multiplied by radius (½ of the width) of the room.

Look up the recommended amount of lumens (or candlefoot or luxes) needed for a given activity in the office at CIBSE.org. For instance, CIBSE recommends at least 500 lumens for general office spaces used for computer, reading and filing activities. Note that other professional lighting sources, such as ASID, may give a multiplier for the room being planned. In these cases, calculate the amount of lumens needed by multiplying the amount of square feet of the room by the multiplier provided.

Calculate the number of spaces in the office that can be used to provide lighting.

Divide the total recommended lumens for the entire office space by the amount of lighting spaces planned.

Purchase light bulbs that supply at least the amount of lumens needed. Look for the lumens (also called candlefoot and luxes) on the lightbulb's packaging.
References
 "Lighting Design Basics;" Mark Karlen and James Benya, 2004
 "Interior Lighting, Fourth Edition;" Gary Gordon, 2003
 CIBSE.org  Chartered Institute of Building Services Engineer  office lighting recommendations
 Photo Credit Fluorescent overhead lamp in office image by Alexey Kuznetsov from Fotolia.com