This statement indicates the type of confusion that is
created by use of the undefined term "full spectrum."
Considering that standard incandescent lamps are very close
to being blackbody radiators, I can't think of any light
source, except the sun, that has a spectrum that is more
full than incandescent lamps. The "blue"-tinted glass bulb
used on many incandescent lamps to raise their color
temperature actually absorbs energy in a relatively narrow
range of wavelengths. In my opinion, that makes the spectrum
of these incandescent lamps less "full" than a non-filtered
incandescent lamp.
This is true of incandescent lamps whose bulbs are made of "neodymium
glass". "Neodymium glass" has a distinct absorption spectrum, with its
main feature at visible wavelengths being a notable and narrow absorption
band in the yellow, with two points of maximum absorption (one close to
578-80 nm and one close to 589-590 nm).
I have seen the claims of "neodymium lamps" being "full spectrum".
I consider their main benefit being a "color exaggerating effect" - as
in most red objects tend to be rendered more-red and more brightly, and
most green objects tend to be rendered more-green and more brightly, than
under unfiltered incandescent light of the same color temperature.
Neodymium glass, by being bluish, also raises the color temperature.
However, I normally do not consider any of this a reason to use
incandescent lamps that have energy efficiency even lower than usual for
incandescents - the neodymium glass only removes visible light, and does
not make visible light from anything. Energy efficiency of "neodymium
lamps" is less than that of unfiltered incandescents.
Since many "neodymium lamps" with "taller claims" (my words) have
claimed life expectancy of 5,000 hours and vibration-resistant filaments,
I expect their energy efficiency to be significantly less than that of
unfiltered incandescents having 5,000 hour life expectancy and
vibration-resistant filaments. Longer life expectancy and
vibration-resistant filament design both detract from energy efficiency
(which is light output for a given wattage).
The color distortions, despite being at least fairly arguably favorable,
detract from the color rendering index. I don't have an exact figure on
hand but my impression is that neodymium lamps have a CRI around 80, while
unfiltered incandescents have CRI by definition of 100.
There are also incandescent lamps with bluish glass (or bluish coatings)
not involving neodymium. These largely lack any sharp spectral features,
other than often a somewhat to fairly sharp loss of absorption as
wavelength increases from far-red to near-infrared. Sometimes there is
some notable "ripple" in the visible spectrum, but I have never found that
to be truly serious.
My impression is that CRI of those would be in the mid-uper 90's.
My main objection to those is the same as my main objection to
"neodymium lamps" - the filtering removes visible light, reducing the
energy efficiency from that of unfiltered incandescents.
If we are talking about high color temperature filtered
incandescent lamps, perhaps we should call them that instead
of using the term "full spectrum."
Most without neodymium and having color temperature within several
hundred K of 5000 K I would consider candidates for "full spectrum",
except there is no "official definition" of "full spectrum".
I do note that "full spectrum" has no official definition in
"the lighting industry".
I remember a few years ago a thread involving proposal of such a
definition, and I remember proposing such a definition in that thread.
I also remember resistance to any definition of "full spectrum" being
"officially adopted in the industry" (my words) since the biggest winners
of that would be some of the hucksters.
- Don Klipstein (
[email protected])