"misswizz" wrote in message
oups.com...
Hey
Okay maybe if I explain how I did my project then you will know what
sort of an answer i am looking for.

I got three plastic cups filled it up with soil and planted 10 radish
seedlings in each of them. On the first cup I covered it with blue
plastic, on the second cup I covered it with red plastic and on the
third cup I didnt cover it with anything because I wanted to test that
on normal sunlight. I did not use any different coloured light bulbs.I
set my project outside under the sun. I tested the radish seedlings out
over a three week period in the end I discovered that the blue plastic
covered cup the plant grew best in.
My teacher wants to know why that is she wants to know the scientific
idea behind my experiment... i told her, from my research that blue
light helps vegetables grow fastest...then she asks why, i tell her
that it has more of an effect on the plant than red light or norml
sunlight, because red light is better for flowering plants. she still
goes and asks me why...

So really the question that I want to ask you is why did the blue
covered cup help my plant grow at a faster rate.

We need more details of *how* you covered the seedlings with the blue
plastic. Did you cover these seedlings so that there was a free flow of air
(i.e.absolutely free flow) around them? Or did you cover the seedlings with
the blue plastic in such a way that the flow of air was hindered? If you did
the latter, you effectively placed these seedlings in a greenhouse, so that
they grew in a hotter environment than did the seedlings that were exposed
to direct sunlight without a plastic "greenhouse".

Even if you accept this idea, you would still need to explain why the
seedlings under the blue plastic grew better than the ones under the red
plastic. You have received many excellent suggestions to answer this point.
It is worth remarking that plant growth is not the only thing that depends
on the colour of the light. Photographers (in the old days of black and
white photography) used to work in darkrooms that were illuminated by a red
light. This was because the emulsion on the photographic paper was sensitive
to blue/green/yellow light, but not to red. Tanning of the skin, and skin
cancer, are both caused by ultra-violet light, but not (to any significant
extent) by red, green or blue light.

From a physicist's point of view, light arrives as a shower of millions of
"photons" - which are individual packets of light energy (much as an atom
is a individual packet of a given chemical element, or an electron is an
individual packet of electrical charge). The energy of each photon depends
on the wavelength of the light. The shorter the wavelength, the higher the
energy of each photon. Red light has a relatively long wavelength, and each
individual photon has a relatively low energy. To a large extent, therefore,
each photon of red light has insufficient energy to initiate a chemical
reaction. Because the wavelength of blue light is approximately half that of
red, each individual photon of blue light has twice the energy. This extra
energy is often sufficient to initiate a chemical reaction, such as
photosynthesis, but is relatively ineffective in tanning your skin or
causing skin cancer. Ultra-violet light is even shorter wavelength than
blue, has an even higher photon energy, and can cause the chemical reactions
of tanning and skin cancer. The energy of far-ultra-violet light may be so
high that plant leaves might experience more damage than beneficial
photosynthesis if exposed to it. Our eyes may also be damaged by exposure to
excessive ultra-violet light, again because of the high photon energy.

Richard Chambers Leeds UK.