PROPER LIGHTING IN THE HOME 



109 



ington, D.C. This unit of the intensity of light is 

 known as the international candle. 



We have learned, however, that the illumination of 

 an object depends not only upon the intensity of the 

 light source but also upon the distance the object is 

 from the light. A body five feet away from a 100- 

 candle power bulb will receive only one-twenty-fifth 

 as much light as the same body placed one foot from 

 the bulb. To take into consideration these two factors, 

 the unit in which illumination is measured must have 

 both intensity and distance. This unit is called the 

 foot candle. An object one foot away from a one-candle 

 power light source is illuminated with an intensity 

 of one foot candle. A tennis court on a bright sunny 

 day has an illumination of about 10,000 foot candles 

 while some factories working by artificial light have 

 less than one foot candle. 



The amount of illumination needed in our homes, 

 schools, and factories varies. The following table 

 . gives the proper illumination for various conditions. 



Illumination Required for Schools 1 



Assembly rooms 5 foot candles 



Classrooms and studies 10 foot candles 



Cloakrooms and corridors 2 foot candles 



Drawing and sewing rooms 20 foot candles 



Laboratories and manual training rooms 10 foot candles 



Illumination Required for Homes 



Halls and corridors 2 foot candles 



Kitchen 10 foot candles 



Bedrooms 5 foot candles 



Sewing room 10 foot candles 



Porch and basement 2 foot candles 



Bathroom 5 foot candles 



Dining room 2 foot candles 



Living room and library 2 foot candles 



but with 10 

 foot candles 

 under read- 

 ing lights 



The illuminating power of electric-light bulbs is 

 more commonly expressed in watts than in candle 

 power. The watt is the unit of measurement of the 

 power of electricity. The relation between watts and 

 candle power for different electric-light bulbs is 

 known. An ordinary tungsten lamp requires about 

 1.25 watts per candle power. Thus a 60-watt tungsten 

 lamp gives 60 watts -+- 1.25 or 48 candle power of 

 light. How many candle power would a 100-watt 

 tungsten lamp give? Figure 166 shows a device known 

 as a foot-candle meter which has recently been de- 

 veloped for home use. From this instrument the il- 

 lumination of any room may be read directly in foot 

 candles. 



What are the different methods of lighting? Electric 



1 From Lynde, Everyday Physics, by permission of the Mac- 

 millan Company, publishers. 



-rtil Electric Company 

 FIG. 165. TYPES OF HOME ILLUMINATION 



r DIRECT LIGHTING 

 Middle INDIRECT LIGHTING 



Lower SEMI-DIRECT LIGHTING 



