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Each light-mediated plant response has what is called “action spectrum” showing that response as function of the light wavelength. Phototropism is no exception, even though the phototropic response is more complicated than most (it has different behaviors at low and at high light levels). For the purposes of this discussion, we’ll consider only the low light level phototropic response which has been studied since the 19th century. The reference http://biology.mcgill.ca/Phytotron/LightWkshp1994/3.3%20Hashimoto/Hashimoto%20text.htm shows a couple of such spectra in Fig. 1 (you might also want to Google “phototropism action spectrum” for more examples). Regardless of some subtle differences, those action spectra look essentially the same and have a global maximum in the blue spectral region around 450 nm, with very little phototropic action above 500 nm (dropping to zero by 510 nm). This means that 520 nm green light is completely ineffective when it comes to phototropism.