Illumination is measured in lumens using an illuminometer such as [http://www.sekonic.com/products/i-346/overview.aspx Sekonic]. The [https://en.wikipedia.org/wiki/International_System_of_Units SI] measurement of illumination is lux, or one lumen per square metre (about 1/10 foot-candle). A lumen is the amount of light falling on a surface. A foot-candle is one lumen distributed over one square foot.
The illumination required for casual reading is 200-550 lumens/sq metre. The standard for office desks is 500 lumens. Some general guidelines for comfortable living are given in the below table. These are generally in excess of [https://www.abycinc.org/ ABYC] standards but you should check when you build.
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