I don't argue with the technical reasoning behind this statement, and
even if I were I'm certainly not in the position to dispute this with
Dr Roberts. However, I would say that there are valid reasons for
white LED content below 400nm. Namely, the excitation of fluorescent
whitening agents in clothing, papers, and other materials which is in
the 360-400 range. Hence white LED illumination will lose this feature
in comparison to existing illumination methods. I realize this will
not be compelling to many of you, but to folks in the printing and
pulp & paper worlds, it might prove to be very significant.
I have already found that true with 4100K T8 triphosphor fluorescents,
especially with modern electronic ballasts. They produce less UV than
older tech halophosphor fluorescents, specifically "cool white".
It appears to me that a major reason is that the blue phosphor component
in triphosphor lamps of medium and high color temp. absorbs much of the
365-366 nm UV. The halophosphor of older fluorescents passes this
wavelength.
The 404.7 nm wavelength also excites most common blue-glowing optical
brighteners - just to a lesser extent than 365-366 nm. LIkewise, it also
causes some excitation of the blue-glowing component of medium and high
color temp. triphosphor fluorescents. It is also present to a lesser
degree with modern T8 4100K triphosphor fluorescents with electronic
ballasts than with "older tech" "cool white" fluorescents.
- Don Klipstein (
[email protected])
