460 nm is just fine for "normal" purposes of observing fluorescence under water.
Actually I use LEDs of roughly 450-470 nm. The "trick" or trade secret lies in the use of the right excitation filter (a dichroic filter, for greater precision), which "trims" the spectrum (= distribution of wavelengths) of light output from your blue light torch, which is why the exact wavelength within the range 450-470 nm is not so important. See Spectrographs without and with dichroic filter for illustration of this.
However, it is true that different fluorescent pigments have different maximum excitation wavelengths. Nevertheless the best compromise (to see as many fluorescent colours as possible) is blue light of 450-470 nm.
In order to excite red fluorescence, for example, excitation light in the green part of the spectrum (530-550 nm) is slightly more effective than blue light.
See Investigating red fluorescence with a green excitation light for illustration (note that you can play several of these videos at the same time for easier comparison by clicking on "play" of two or more videos in rapid succession).
As you can see in these example videos, with green excitation light (and a red camera filter) you see only red fluorescence, but no other colours.
Another option would be to use UV light, but this has many disadvantages, see Ultraviolet versus blue excitation light.
Actually I use LEDs of roughly 450-470 nm. The "trick" or trade secret lies in the use of the right excitation filter (a dichroic filter, for greater precision), which "trims" the spectrum (= distribution of wavelengths) of light output from your blue light torch, which is why the exact wavelength within the range 450-470 nm is not so important. See Spectrographs without and with dichroic filter for illustration of this.
However, it is true that different fluorescent pigments have different maximum excitation wavelengths. Nevertheless the best compromise (to see as many fluorescent colours as possible) is blue light of 450-470 nm.
In order to excite red fluorescence, for example, excitation light in the green part of the spectrum (530-550 nm) is slightly more effective than blue light.
See Investigating red fluorescence with a green excitation light for illustration (note that you can play several of these videos at the same time for easier comparison by clicking on "play" of two or more videos in rapid succession).
As you can see in these example videos, with green excitation light (and a red camera filter) you see only red fluorescence, but no other colours.
Another option would be to use UV light, but this has many disadvantages, see Ultraviolet versus blue excitation light.
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