MadSci Network: Botany
Query:

Re: why do plants grow better with fluorescent light than incandescent?

Area: Botany
Posted By: Marcy LaViollette, Senior, chemical engineering, Capital High School
Date: Thu Oct 30 23:58:23 1997
Area of science: Botany
ID: 877555137.Bt
Message:
The simplest answer to that question is the fact that fluorescent light is 
more like natural sunlight than incandescent.  By more alike, I mean that 
the emission line spectra of fluorescent light and sunlight are nearly the 
same.  An emission line spectrum is a pattern of colors that is as unique 
to a kind of light as a fingerprint is to us.  It is used to tell different 
kinds of light apart and different elements apart.  To see an emission line 
spectrum, you must have a special instrument called a spectroscope.  When 
placed at the proper angle to the light source, a rainbow will appear.  
This is illustrated in the picture below.  


This rainbow will most often be missing many colors in it.  A scientist can 
tell which kind of light it is by which lines are missing.  White light is 
made up of all possible colors (wavelengths) of light combined.  The whole 
spectrum is pictured below, you know it as the rainbow.  


Plants need two main colors (wavelengths) of light.  Red and blue.  Green 
light is not used.  It is deflected towards your eye, this is why plants 
appear green.

If you were to look through a spectroscope at incandescent light, you would 
notice the prominent red lines.  When red light is used alone on plants, it 
tends to produce leggy plants. The bulbs also produces a lot of heat in 
comparison to the amount of light given off.  Cool white and warm White 
fluorescent tubes, used together, produce the best light for plant growth. 
Cool white emits light in the blue wavelength while warm white emits light 
in the red range.  These two when used in the correct balance, much like 
sunlight, will grow healthy plants.  

Keep asking questions! :]

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