82 



THE FLOWERING PROCESS 



Beltsville, Maryland, a large carbon arc lamp is used as the source, 

 and the light is broken into the various regions of the spectrum by 

 passing it through a prism (see Chapter 7). This apparatus has 

 provided considerable information about the response of plants to 

 light. We are presently building a light flasher which will use a 

 Xenon arc lamp, a set of shutters, water-cooled lenses, interference 

 filters, and other items. 



\ standard 500 Waff 

 \ 

 \ incandescent lamp 



\ 



\ 

 \ 

 \ 



Typical daylight type 

 fluorescent lamp 



-\ h 



-{ \ \ h 



T \ — 



400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 



U.V.I Visible I Infra-red 



WAVE LENGTH IN MILLIMICRONS 



Figure 5-6 

 Spectral distribution of fluorescent and incandescent light. The vertical 

 bars in the fluorescent lamp spectrum are emission lines of mercury. 

 Data such as these are readily available from the lamp manufacturing 

 companies (see also, for an excellent and thorough review of the prob- 

 lems concerned with lighting: Robert B. Withrow and Alice P. Withrow, 

 1956, Generation, control, and measurement of visible and near-visible 

 radiant energy. In A. HoUaender (editor), Radiation Biology 3, 125-258. 

 McGraw-Hill, New York). 



The investigator often apphes the following facts: incandescent 

 light is rich in both red and far-red (far-red can be obtained by 

 filtering through two layers of red cellophane and two layers of blue 

 cellophane), while fluorescent light is rich in red but has essentially 

 no far-red (see Fig. 5-6). Pure incandescent light acts primarily as a 

 red source, even though it contains more far-red than red, because the 



