usually too low for growth of many 
kinds of plants, even on the window 
sills. However, plants can be grown 
quite successfully with artifical light 
in complete absence of sunlight. 
Beans, tomato, cereals, and many 
ornamentals that grow in open sun- 
light make satisfactory growth if the 
artificial light intensity is about 1,000 
foot-candles. Shade-loving plants, 
such as African-violets, begonias, 
episcias, gloxinias, and orchids, will 
grow well with intensities as low as 
500 foot-candles. 
A practical source of artificial 
light for plant growth is the fluores- 
cent lamp. These lamps supply the 
necessary intensity without excessive 
heat and are available in various 
lengths, wattages, and colors, They 
are usually operated on one- or two- 
lamp ballasts, which maintain the 
proper current and provide the start- 
ing voltage. Prewired lamps and 
ballasts of several sizes andtypes are 
available as commercial luminaires 
or as channels. 
Many kinds of plants can be grown 
satisfactorily with only two 40-watt 
fluorescent lamps. As the lamps 
themselves are relatively cool, the 
plants may be placed quite close to 
them without danger of excessive heat 
or burning. Table 1 shows the illum- 
ination at various distances from two 
40-watt cool-white fluorescent lamps 
mounted 2 inches apart. If the lamps 
are mounted further apart, the illum- 
ination at 6 inches or less from the 
lamps is markedly decreased. 
If the daylength is to be controlled, 
plants must be put into complete 
darkness at the close of a particular 
photoperiod. A dark chamber can be 
made of Masonite or plywood with 
calked seams, or it could be made of 
two or more thicknesses of black 
sateen cloth stretched over a wooden 
frame. If used carefully, a cardboard 
box with all seams and joints sealed 
with paper tape could be placed over 
the plants to provide darkness. 
Experimental procedures can be 
facilitated and made more exact if 
an electric time switch is available 
to turn the lights on and off at any 
desired time. 
TABLE 1,--Illumination in foot-candles at various dis- 
tances from two or four 40-watt standard cool-white 
fluorescent lamps mounted approximately 2 inches from 
a white-painted reflecting surface 
Illumination 
from lamps Two lamps Four lamps 
(inches) 
ODARNALRWONE 
1 Center-to-center distance between the lamps was 2 
inches, 
2 These lamps had been used for approximately 200 
hours. 
Demonstrations D-1 through D-4 
show some of the effects of the rela- 
tive lengths of day and night on plant 
growth and _ reproduction. These 
demonstrations tell us that: 
@Some plants flower on short days 
and long nights, whereas others 
flower on long days and short 
nights. 
~*~ 
