think of it like this: a change machine converts a dollar bill to a quarter, and keeps 75% of the money. every time you put a dollar bill, you get a quarter. Now if you throw a whole bunch of different bills at the machine, only the 1 dollar bills will make a difference, and it will always give out quarters. Chlorophyll only absorbs a certain wavelength (in the UV spectrum if I am not mistaken) and gives out red.

I think it’s not right. As I remember, we had some other colours, maybe black… Chlorophyle absorbs red and blue light, but it reflects green light. Find it somewhere, I’m not sure 🙂

look up the definition of fluoresce.

as miloshic said chlorophil a absorves in red and blue. Blue light is much more energetic than red, so when a blue photon strikes the chlorophil, it change from a basal state to a very excited state. To get to a lowest excited state it loses energy by heat. When striked by a red photon, chlorophil changes to that lower excited state and to get to the basal state it looses energy by re-emitting red photons.
Thats why chlorophil a always fluoresce on red…

This is gonna be long…but if you have the patience…it will explain everything to you. =)

If the chlorophyll is placed under a strong light, especially one with a lot of ultraviolet, it can look red due to a process called
"fluorescence," which is the release of absorbed energy in the form of light. Chlorophyll fluoresces red light.

Why red? You may have learned that different colors of light
have different energies. For example, in a rainbow, red light has the least energy, and violet has the most energy. Chlorophyll is able to absorb different colors of light, especially red and blue light. The relatively weak red light causes chlorophyll’s electron to jump one "energy level." Since blue light has more energy, it excites the chlorophyll’s electrons even more: They jump two levels. (Ultraviolet has even more energy.) However, it’s very difficult for the electron to stay at such high energy in a chlorophyll molecule, so the electron falls very quickly from the blue energy level to the red energy level. (The extra energy is lost as heat.)

OK: now all of the energy associated with the chlorophyll is "red" energy. When the chlorophyll is properly arranged in the chloroplast, that red energy is used to do the work of photosynthesis. However, if you take the chlorophyll out of the chloroplasts, there’s no place for the energy to go, except heat or light! Much of the energy is released in the form of red fluorescence, so the chlorophyll looks red.

Chlorophylls reemit a fraction of the light energy they absorb. Irrespective of the absorbed light, the emitted fluorescence is always on the long-wavelength side of the lowest energy absorption band, in the red or infrared region of the spectrum.
The fluorescent properties of a particular chlorophyll are functions of the structure of the molecule and its immediate environment. Thus, the fluorescence spectrum of chlorophyll in the living plant is always shifted to longer wavelengths relative to the fluorescence spectrum of a solution of the same pigment. This red shift is characteristic of chlorophyll.