As i'm reading the Softsecrets 03-2009 page 16. right bottom of the page, Its article from Ed rosenthal. He says that we can keep the pure blue light on at night!!! the flower cycle wont be desturbed and the plants will benefet and give bigger buds...

I quote Ed Rosenthal:" plants use blue light for certain regulatory processes and also for photosynthesis. Chlorophyll absorbs both blue and red light and uses the light energy to power the complex process in which water and atmospheric carbon dioxide are converted to sugar and oxygen gas. Blue light does not affect the regulation of flowering.

When blue light is turned on during the dark periode, plants photosynthesize but their flowering isn't affected. This results in more growth as the plants produce more sugars. Before LED light it was diffficult to create a pure blue light. Instead, most of the time other spectrums were filtered out. Which can be an inconvenient process.''



source: http://www.softsecrets.nl/?id=47&title=Issues issue 03-2009 page 16
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So next LED grow, that will be whit one 600Watt Spectra unit. I keep a pure Blue LED light on during the dark periode...