Victor Roberts wrote:
[snip]
However, the potential for a better incandescent lamp is
still there. As opposed to some other ideas we have heard
about, the 100 lm/W incandescent lamp does not violate any
laws of physics and requires /only/ the solution of material
science issues.
Yes, in theory. However if the total number of requirements and/or
constraints of such technology are of the same type as those of, say,
controlled fission or fusion, then I don't think it would be of much
practical use.
Both a tungsten filament and the sun are essentially black body
radiators. The tungsten filament achieves a mere 10-30 lm/W (depending on
wattage and type), while the sun achieves a whopping 98 lm/W.
This difference tells me something: that in order for us to be able to
realize efficiencies of the order of 90-100 lm/W using black body
technology, we better have some new nifty theories behind the final
application.
We do have controlled fission of course, but I certainly do not expect
nuclear reactor cores radiating close to criticality to be the light
sources of choice any time soon
Absent fission and fusion, I really cannot see how one can force any
material to realize temperatures close to 5785 K, without facing some
serious containment problems.
I think Vic was talking about HIR and also filaments with IR emission
impaired - maybe along the lines of whatever got mentioned here a few
years ago by using crystal size or something along those lines to make
tungsten radiate effectively only in the visible. If enough development
goes into things along these lines and they succeed, then maybe we can get
100 lm/W with temperatures in the 3000K or low 3,000's K ballpark.
Then there are gas mantles. They radiate very selectively, radiating
very little IR and having emissivity reduced at many, maybe most
red/reddish wavelengths. It appears to me that they achieve a temperature
close to the actual flame temperature (maybe achieving 1900 K or so?),
incandesce at a brightness easily explainable by such a temperature even
with inpaired red radiation, and have a reasonably incandescent color -
just with CCT well above their actual temperature and color somewhat on
the greenish side.
Gas mantles have their radiating constituent having emissivity varying
not only with wavelength, but also with temperature. It appears to me
that the radiation is from some electron transition between 2 different
energy level bands, the lower one of which is not the "ground state".
This means that emissivity would increase as temperature does. I suspect
that explains why gas mantles are white at room temperature, but when
heated in direct sunlight, take on a brownish tinge as temperature is
increased until their incandescence makes it impossible to see their own
color. The older formulation with thorium did that more visibly than the
more modern formulation.
I wonder if an arc tube can be made of a similar material and an HID
lamp can be made with such an arc tube in a vacuum-containing bulb. To
maximize luminous efficacy, one only needs to minimize electrode losses
and arc radiation of invisible wavelengths that pass through the arc tube
(probably mainly infrared). If the arc tube gets to the low or mid
2,000's Kelvin and promises to last, looks like we have an efficient
selectively-visible-radiating incandescent light source. If it gets much
past the temperature of a propane torch, it would probably have CCT hardly
higher than that already achieved by gas mantles (notably having CCT
changing little as brightness varies greatly directly with temperature).
The higher temperature, higher emissivity with higher temperature, and
reduced discrepancy between CCT and actual temperature may make the darn
thing a little less greenish.
The arc may not need to be efficient at radiating anything - but would
conduct heat to the arc tube. I suspect that argon at about an amp
and pressure in the fractional atmosphere to few atmospheres ballpark
likes to be very inefficient at radiating anything, though could blow up
its radiation of near-IR lines with power input past 15-20 watts per
centimeter after electrode losses. Neon probably radiates little around
ballpark-atmospheric pressure at 20-30 or less watts per centimeter -
probably mainly visible, heavily at red wavelengths - and portion of that
passing through the arc tube would probably be welcome to adjust the
color of the arc tube's incandescence that would be a greenish variant of
broadband incandescence having CCT in the mid-3,000's K - even if a bit
less greenish than gas mantles. The neon reddishness may get the CCT to
close to 3,000 K and the chromaticity impressively close to that of
blackbody - and CRI may achieve mid-upper 90's, with main error being from
shortage of shorter bluish wavelengths around/under 450 nm.
(Given existence of ceramic arc tube metal halide lamp technology, a
trace of an indium halide might improve upon the above if the arc tube is
not completely opaque to the 451 and 411 nm wavelengths of indium. Heck,
metallic indium may produce enough vapor to achieve a majority of what
would be desired from indium.)
And I would use pure neon rather than 99.5%-neon-.5%-argon, which has
significant near-infrared emissions of argon. Pulse start and other
ballasts achieving boosted volatge for starting are established well
enough for metal halide lamps that I think an incandescent-arc-tube lamp
with pure neon (and maybe a trace of indium) and M-whatever ANSI
"ballast-compatibility" codes could be a way to go.
- Don Klipstein (
[email protected])
