Action Spectra - Spectral Sensitivity and Effectiveness

(This is an growing archive and information page on action spectra. If you know some more action spectra or background information we would welcome you to contribute to this site.)

Special thanks for contributing with original data (in alphabetical order) to :L.O. Björn, M.M. Caldwell, F. de Gruijl, S.Flint, D.-P.Häder, M.F. Holick, S. Madronich, R.B. Setlow, T.Swartz, L.Taiz, Y.Takeuchi,




Biological effectivity:
An action spectrum describes the spectral effectivness of a photobiological or photochemical process. They are presented as plots, tabled values can be provided later. Weighting the spectral irradiance of a source with the action spectrum followed by an integration over the whole spectral range delivers the biologically effective irradiance Ebiol. Under clear sky Ebiol depend in first order on the total ozone content of the atmosphere (O3) and the solar heigth above horizone (sh). Ebiol plots are given for each biological effect below. The change in Ebiol due to a change of 1% in O3 is often described by the RAF which depends again on O3 and sh. Below the RAF is calculated as: RAF=dE[%]/dO[1%] and given as plot.
The biologically effective dose Hbiol is gained by taking into account the time of exposure.

Many processes show a continously direct relation between effect and dose. Some effects stop at a certian level even if the dose is still increasing. Some others occur only if a certain threshold (radiatiant exposure) dose HT is exceeded. For such effects treshold spectra are given as plots (if data are available).
Effects can be distinguished by the latent time, occuring immediately or with delay. Some effects are reversible others are not. Further they can be grouped in being damaging, vital and protective.

Gaining an action spectrum:
Action spectra may be derived in vivio, in vitro or in situ. The light source can either be monochromatic or polychromatic. This can make a difference if an effect is not wavelength additive, but synergetic. This means that a serie of irradiation with monocromatic light of different wavelengths do not cause the same effect as irradiation by all at once.
An action spectra can not always be derived direct from volunteers. Such effects are then often studied indirect in using a model. For the human for example effects are studied in animals (e.g. hairless mice) and then transformd to the human by changing or addinge an parameter (e.g. skin trasnmittance,...)

Information from an action spectrum:
The action spectrum for formation of photoproducts photoproducts might be expected to resemble the absorption spectrum of the molecules responsible for these photoproducts, although several conditions need to be fulfilled for this to be case (Jagger 1985). Nevertheless, comparison of experimentally determined action spectra with the absorption spectra of appropriate molesules can sometimes give insight into the molecule primarily responsible for the effect. For example, in 1928 Gates showed that the bactericidal action of UVR of different wavelengths in Staphylococcus aureus cells closely matched the absorption spectra of nucleotide bases. This observation was confirmed with other unicellular organisms (
figure 4) and led to the realization that nucleic acids have a fundamental role in ultraviolet photobiology. More recently, comparison of erythema action spectra, in patients with possible drug-induced photosensitivy, with the absorption spectra of suspect agents can confirm the diagnosis (Diffey and Farr 1988).

Sources of action spectra:
During the past many photobioogical or photochemical effects were found. For a variety of them the corresponding action spectrum could be derived. Many action spectra are published rather schematically by scatter or line plots than in tabled form. Applications are therefore often done with values taken from a plot which may lead to uncertainites especially at logarithimic scaled plots. In many cases effectivity is given for distinct wavelengths. These points are mostly vanishing when later on shown as line-graphs, etc. (see interpolation or Lost original data)
Up to now even peer-reviewed journals do not care on the authors source of an action spectra.

Interpolation, approximation and extrapolation:
Action spectra are derived for certain wavelengths. Model calculations however need relatively high spectral resolution for weigthing the spectral irradiance. Therefore another point of concern is interpolation. Linear interpolation may be appropriate for slopes within one magnitude. If the nature of an effect is rather logarithmic then linear interpolation leeds to bumps on a logarithmic scale(d plot).

History of action spectra:
Some of the action spectra have a long history dating back to the first decades of the last century. The action spectrum for the erythema as an example was already published by CIE in 1935. A continous work of improvement, technical advance, summarising, or dividing leads to different versions which are often used parallel at the same time. To comprehend earlier studies the availibility of a collection of historical action spectra is also of advantage.
A variety of action spectra were not derived over the whole UV range. Extrapolation in the UVA may result in noticeable errors since solar irradiance is magnitudes higher than in the UVB.

Lost original data of action spectra:
Many action spectra (when not published in tabled form) can only be retrieved due digitizing the curve from an published paper. Especially for older action spectra original data are not available respectively the author can not be contacted. Sometimes private communication may help.

Measurements of biologically effective radiation:
The proper way to measure biol. effective radiation is using a spectrophtometer with high resolution. This technique is expensive and need operators with high experience. A cheaper and less sophisticated method is to use broadband meter. The spectral sensitivity of broadband meter hower does not fit the action spectrum perfectly. Corrections are necessary depending on the atmospheric parameters which change the sepctral distribution of sun ligth (O3, sh, clouds, altitude, ...).

This collection should help to solve some of the mentioned problems. A special side for tabled values will be comming up soon.





Phototoxic Reactions:


Human General Risk:


Skin Cancer:

Skin cancer associated with exposure to UV are the basal cell carcinoma, squamous cell carcinoma and curaneous melanoma. The first two result from the malignant transformation of keratinocytes. The later results from malignant transformation of melanocyten (pigment producing cells).



Pigmentation is strategy to counteract high radiation levels. Immediant pigmentation results from oxydative mealnin darkening, which is reversible. It occurs after receiving a threshold dose and vanishes depending on the received days after minutes or days. After receiving a certain threshold dose, melanin pigments are built up and spread. Delayed pigmentation vanishes after weeks.


Immune suppression
The UVB activated photoreceptor urocanic acid regulates immune suppression in mice. The same compound exists on other mammalian skin, including human skin.


Vitamin D3:

Vitamin D is formed in the skin after exposure to ultraviolet radiation (and is also absorbed from diet). It is hydroxylated at the liver to 25-hydroxyvitamin D (25(OH)D), and again in the kidney to 1,25-dihydroxyvitamin D (1,25(OH)2D), which is the active form (Schemata). Effective dose is assumed to be less than 1MED.








Mycrosporint-like amino acids (MAA) are photoprotective compounds. Cynobakteria, Phytoplankton, Macroalgea or Seagras produce MAA as strategy of phtoprotection.







Action Spectra in the UVA and Visual range



Light plays also a major role in orientation of non-photosynthetic organisms which use ligth as a directional cue to move. Movements are done also to avoid high irradiance or to avoid radiation of harmful wavelengths. It is thougth that in many ciliated protozoa photo-orientation additionally serves nutritional needs or to avoid predators.



Spectral Sensitivity of broadband meter





Diffey B L and Farr P M 1988 The action spectrum in drug induced photosensitivity Photochem. Photobiol. 47 49-54

Errera M 1952 Etude photochemique de l'acide désoxyribonucleique I. Mesures énergétiques Biochim. Biophys. Acta 8 30-7

Gates F L 1928 On nuclear derivatives and the lethal action of ultraviolet light Science 68 478-80
Harm W 1980 Biological Effects of Ultraviolet Radiation (Cambridge: Cambridge University Press)
Jagger J 1985 Solar-UV Actions on Living Cells (New York: Praeger) pp 174-6



Patrick M H and Rahn R O 1976 Photochemistry of DNA and polynucleotides: photoproducts Photochemistry and Photobiology of Nucleic Acids vol II ed S Y Wang (New York: Academic) pp 35-95




Last modification: July, 2003 alois.schmalwieser()