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Do some flowers fluoresce? Some deep purple Lobelias and larkspurs seem to glow and confuse my eyes in sunlight. It reminds me of those blue LED Christmas lights (they come in strings with other colors) - the blue ones only seem to be showing two colors at once.

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Many flowers fluoresce under the influence of UV and white light. The compounds that fluoresce are called Betalains, and are either red/purple (betacyanins) or yellow (betaxanthins).

It is thought that this is a method of making the flowers more obvious to insect pollinators. However, there is some debate about whether the fluorescence contributes to this much compared to just the bright colours.

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  • $\begingroup$ Fluorescence is a way of making brighter colors, though. Ever looked at day-glow colors under UV light? It's also common to fluorescent chemicals ("optical brighteners") in laundry detergents, in order to make colors (especially whites) appear brighter: en.wikipedia.org/wiki/Optical_brightener $\endgroup$
    – jamesqf
    Jun 21 at 17:11
  • $\begingroup$ @jamesqf - that's exactly the point of the papers linked in my second paragraph. It isn't known how much the fluorescence contributes to attractant for insects as the colours are already bright in the ranges that insects use. Fluorescence always puts out less energy than is put in because of the energy cost of the electron excitation step, so while those colours may be bright under UV alone, with the additional very bright white light spectrum, the fluorescence is somewhat lost. $\endgroup$
    – bob1
    Jun 21 at 22:23
  • $\begingroup$ We may be thinking about different things. I'm not thinking of UV colors that are visible to some insects & birds, but of fluorescence absorbing the incident UV light and re-emitting some of the energy in the human-visible range. Just as for instance day-glo orange is orange under inside lights (no UV), emits nearly the same shade of orange when you illuminate it with a UV light in the dark, and is really bright orange in sunlight because both oranges combine. $\endgroup$
    – jamesqf
    Jun 22 at 6:11
  • $\begingroup$ @jamesqf, no, that's what I am talking about too. The evidence for significantly brighter signals for plants emitting in the visible spectrum isn't there. It looks like <10% increase in brightness. $\endgroup$
    – bob1
    Jun 22 at 8:25

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