Re: Do Plants Grow Better In Sunlight or Artifical Light? Why?

Complete question:

I need to know this for our Science Fair in March 2001.  I also need to 
know the effects that each type of light has on plants.  How can I test to 
find out?  Thank-You.

Reply: 

Plants can grow just as well, if not better, under electric light than with 
sunlight if the amount, quality, and duration of the light are optimum. The 
quality of light is the wavelength composition. Sunlight has a roughly equal 
amount of light of all colors. An incandescent bulb produces much more red than 
other colors. Flourescent lamps, such as the standard Cool White, has less red 
than sunlight or incandescent and may produce slightly shorter plants.

The best types of electric light for plant growth are fluorescent and high 
intensity discharge lamps (HID). HID lamps are of several kinds including high 
pressure sodium, a type often used in street lights. Incandescent light 
produces a lot of heat and not much light so is not as good for plant growth. 

It is difficult to fairly compare sunlight and electric light because it not 
easy to get the same amount of light from each source. It is easier to compare 
different types of electric light, such as Gro-lux versus Cool White 
fluorescent bulbs. 

It is also easy to compare light amount and duration with one, two or more 
fluorescent light banks. Timers can be used to change the duration, for example 
12 versus 18 versus 24 hours of light per day. Plants can be set at different 
distances beneath a fluorescent light bank to give differing light intensities.

I do not recommend experiments that use colored cellophane to grow plants under 
different light colors because it requires expensive equipment not available to 
students in order to get the same amount of light for each color. Without 
having the same amount of light for each color, you cannot know if plant growth 
is affected by light color or light amount.



References

Hershey, D.R. 1995. Plant Biology Science Projects. Wiley: New York.


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