Anonymous

# 慳電膽 -- for eye health

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• 天同
Lv 7

Let us treat this problem in a scientific way.

The illuminance at a residence should be in the range from 100~300 lux (lumen/m^2), as given in the Code of Interior Lighting produced by the Chartered Institute od Building Services Engineers. Please refer to the follwoing web-page:

http://www.arca53.dsl.pipex.com/index_files/lightl...

Taking an average illuminance of 200 lux at the dining room, and assume that your dining room has a height of about 3 m, the luminous flux at a compact flouresent lamp (CFL) installed at the ceiling is

= 200 x (4.pi.3^2 ) lumens = 22600 lumens

where pi = 3.14159...]

To produce 22600 lumens, a CFL of 340 watts is needed. See the follwoing web-page, at the table under "energy efficiency"

http://en.wikipedia.org/wiki/Compact_fluorescent_l...

However, the above simple calculation assumes no reflection of light from the walls, ceiling and floor; and also the light comes from a single light source.

In the actual practice, you could reduce the CFL wattage by nearly half if shiny wall finishes have been used. Also, by spreading the light source into about 5 evenly spaced CFLs over the 100 square feet room, then each CFL should be of power 34 watts,

Notice that the above calculation is only a crude estimation. As the average illuminance at the room depends to a large extent, the decoration inside the room and the wall finishes, which reflect light to different extent. A room with dark coloured wall definitely needs more CFLs than walls with bright colours.

• Anonymous