An action spectrum is a graph of the rate of biological effectiveness plotted against

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

. It is related to absorption spectrum in many systems. Mathematically, it describes the inverse quantity of light required to evoke a constant response. It is very rare for an action spectrum to describe the level of biological activity, since biological responses are often nonlinear with intensity. Action spectra are typically written as unit-less responses with peak response of one, and it is also important to distinguish if an action spectrum refers to quanta at each wavelength (mol or log-photons), or to spectral power (W). It shows which

is most effectively used in a specific

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

. Some

reactant In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

s are able to use specific wavelengths of light more effectively to complete their reactions. For example, chlorophyll is much more efficient at using the red and blue regions than the green region of the light

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

to carry out

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. Therefore, the action spectrum graph would show spikes above the wavelengths representing the colours

red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...

and

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...

. The first action spectrum was made by T. W. Engelmann, who split light into its components by the

prism Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry), a kind of polyhedron Prism may also refer to: Science and mathematics * Prism (geology), a type of sedimentary ...

and then illuminated ''

Cladophora ''Cladophora'' is a genus of reticulated filamentous Ulvophyceae (green algae). The genus ''Cladophora'' contains many species that are very hard to tell apart and classify, mainly because of the great variation in their appearances, which is a ...

'' placed in a suspension of

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. He found that bacteria accumulated in the region of blue and red light of the split

. He thus discovered the effect of the different wavelengths of light on

and plotted the first action spectrum of photosynthesis. Further examples include suppression of melatonin by wavelength and a variety of hazard functions, related to tissue damage from visible and near-visible light.

References

External links

Plant Physiology Online: Principles of Spectrophotometry
Photosynthesis Absorption spectroscopy {{spectroscopy-stub

See also

References

External links