HMI vs Xenon?
Saberfire
I have heard that HMI lights produce more Lumens per Watt the Xenon's
do. Does anybody know how much of that is in the visible light spectrum?
--
Thanks,
Bob Bristow
Bob Knowlden
Lumens are, by definition, visual units. A megaWatt laser operating at 1.3
microns makes zero lumens -although you might get visible light created as
it torches off a plasma at the target.
I have no experience with HMI lamps (an Osram trademark). The 5600K color
temperature (close to sunlight) sounds efficient.
They don't sound distinctive enough to be attractive as headlamps in luxury
automobiles though. (I've always thought that the main purpose of the HID
lamps in those cars was to shout, "I'm what God would be like - if only He
had the money!". Halogen are available in any brightness you like, well up
into the extra-legal range. I doubt that the high-color-tempearture lamps
are justifiable in terms of visual acuity.)
Bob Knowlden
Spam dodger may be in use. Replace nkbob with bobkn.
"Saberfire" <b...@bristow.com> wrote in message
news:GyyA9.2$yn.4...@newsrouter1.sac.winfirst.net...
Doug Dulmage
>All of it.
>
>Lumens are, by definition, visual units. A megaWatt laser operating at 1.3
>microns makes zero lumens -although you might get visible light created as
>it torches off a plasma at the target.
>
>I have no experience with HMI lamps (an Osram trademark). The 5600K color
>temperature (close to sunlight) sounds efficient.
>
>They don't sound distinctive enough to be attractive as headlamps in luxury
>automobiles though. (I've always thought that the main purpose of the HID
>lamps in those cars was to shout, "I'm what God would be like - if only He
>had the money!". Halogen are available in any brightness you like, well up
>into the extra-legal range. I doubt that the high-color-tempearture lamps
>are justifiable in terms of visual acuity.)
>
>Bob Knowlden
Sorry to piggy back here. HMI's have a fairly flat curve relative to the
different wavelengths, more of a broadband source compared to some
fairly high spikes that are found in xenon and krypton lamps.
As far as the arc lamps for vehicles, those types are known as HTI's
vs. HMI and have a little different curve to them, as well as slightly
better color renditioning numbers if I remember. The whole idea of using
the HTI lamp as developed by Osram was not so much as a status symbol,
or a means to blind as many oncoming drivers as possible. It is part of a
much broader program where there are heads up displays in the works that
require both IR and UV to do their jobs, the UV for fog penetration, and I'm
not sure exactly what they are using the IR for, except possibly to make
wildlife or humans stand out more in darkness. Years ago I was building high
intensity fiber optic illuminators using a 250 watt version of the HTI lamp
that is packaged as either a standalone lamp for use in your own collection
system, and then also some prefocused modules for use in LCD and light
valve video projectors. There was a research automotive lamp available to
OEM's called the D20 if I remember, and it was a tough lamp to build as
these things have to fit some pretty hard to make specifications set by
vehicle safety standards. Things like being able to do an instant hot restrike
which is tough with xenon, being able to ignite them at temps down to -40F,
again tough for most arc lamps, and of course long life as well as a small
arc as possible as future plans at that time also called for unified auto
lighting where a single lamp could be used for all turn and brake signals by
pumping the light over a common fiber, and then using eletromechanical
vanes at low current to flash them, etc. This also has a bit to do with the
move to going to a 48volt standard for automotive use as it lowers a lot
of the copper requirements.
So, in the long run, you should be able to look up online at Osram
the specs for HMI lamps, taking into account that you also want to look
at the color rendition numbers if you're using it for film or video work, the
higher the better. So, it's not only raw lumen output, as if you're using this
for film lighting and you find that the xenon has too much blue, you may have
to put a lot of tungsten correction filters on which cuts down on the light,
where the HMI may have less output, but because of the better color
renditioning, you don't have to cut the output with filters. Also, you can
do things with the HMI and HTI power supplies that you can't do with xenon
supplies, and again this is more geared to film or television use.
Osram's web site will have all the info that you need, otherwise any
professional lighting or film equipment rental supply company will have
catalogs that have the relative light curves and effeciency charted out
for the different lamp types, and especially Osram as they make every
type lamp and tend to be less biased.
Good luck!
Doug
Sven Hegewisch
>
>It is part of a
> much broader program where there are heads up displays in the works that
> require both IR and UV to do their jobs, the UV for fog penetration, and I'm
> not sure exactly what they are using the IR for, except possibly to make
> wildlife or humans stand out more in darkness.
Are you shure that UV penetrates fog better than IR?
Scattering on small particles goes up with the 4th power of frequency,
so I believe that IR would be better for fog penetration.
( Long ago yellow light was used for "fog lamps" ).
Sven
Saberfire
did forget to mention what I will be using these lights for, which will be
searchlights. I have heard a lot about HMI and Xenon lamps. I am just
trying to figure out what would be brighter....A 6000W HMI Lamp, or a 6000W
Xenon lamp in the same housing. How big of a visible difference would there
be?
--
Thanks,
Bob Bristow
"Sven Hegewisch" <Sven.He...@Physik.Uni-Muenchen.DE> wrote in message
news:3DD361F6...@Physik.Uni-Muenchen.DE...
Don Klipstein
> I really appreciate all the great info all of you have provided me.
>I did forget to mention what I will be using these lights for, which will
>be searchlights. I have heard a lot about HMI and Xenon lamps. I am
>just trying to figure out what would be brighter....A 6000W HMI Lamp, or
>a 6000W Xenon lamp in the same housing. How big of a visible difference
>would there be?
I have seen the spectra of searchlights (I sometimes carry around a
diffraction grating) and I can tell you that they normally use xenon.
Although a short arc xenon lamp produces only about half as much light
as an HMI of the samw wattage and short arc xenon lamps do not last as
long as HMI lamps, the xenon arc is a lot smaller and a similarly smaller
reflector can be used to achieve a beam of the desired divergence (more
like lack thereof).
I remember asking a couple searchlight operators years ago what they
used, and they told me not only xenon (one said mercury-xenon, although
since then I have seen only pure xenon spectra), but the wattage. I
somewhat remember those trucks with 4 searchlights on them have either a
500 watt or a 1,000 watt lamp in each individual light.
Higher wattage lamps have larger arcs, and you will need to have a
larger reflector to get a given shape/divergence beam. Light emitted
per unit area of arc surface is not a whole lot higher in higher wattage
lamps than in lower wattage ones. You will need to increase reflector
area almost proportionately with lamp wattage if you want the same
divergence beam as another lower wattage searchlight.
- Don Klipstein (d...@misty.com)
Doug Dulmage
Well, to be honest, it was a fairly short story in one of the laser trade
magazines about using arc lamps in vehicles, as well as what the
current technology in heads up display were. So, this I believe was
a program being run by BMW along with Osram and they did make
a point of saying that there were two spikes in that HTI lamp that were
of interest for the heads up display, one being UV for fog, and then IR
for animals and pedestrians. They didn't go into great detail about any
particular windows in the fog that worked better in the UV, however I
think part of the article mentioned that by using this wavelength with the
particular detector that they had in mind, it allowed for the visible light
to be attenuated for both the benefit of the driver and oncoming vehicles
by dropping in a UV bandbass filter, and then the detector would present
the data on the HUD while allowing the drives pupils to open up more than
usual. This article is a bit old, I'd say about 4-5 years ago, but I have
heard that there are vehicles available in Europe now that have the HUD's
in them, whether they are using IR or UV or both, I don't know, but I would
imagine that it would either be a high end BMW or Mercedes.
As far as IR absorbtion in fog, I know there have been studies done
here in the States for clearing ground fog from military air bases using IR
lasers, mostly the longer wave Co2.
Doug
Doug Dulmage
> I really appreciate all the great info all of you have provided me. I
>did forget to mention what I will be using these lights for, which will be
>searchlights. I have heard a lot about HMI and Xenon lamps. I am just
>trying to figure out what would be brighter....A 6000W HMI Lamp, or a 6000W
>Xenon lamp in the same housing. How big of a visible difference would there
>be?
>
Well, for searchlight use, you'd probably want to use the xenon. This has to
do with the arc size, which in your case, if you want sharp and well
collimated beams, then you need to use the shortest arc possible. I don't
think that even the shortest arc HMI's come even close to being as short
as a xenon in the same wattage. There is a little confusion about brightness
and power when describing arc lamps and such. Briteness in an arc lamp
is a function of the arc size, so it's entirely possible to get more light out
of a smaller wattage xenon lamp with say a 15mm arc than a higher wattage
HMI that has a 30mm arc. This is because you can collect and focus the
smaller arc more effeciently. HMI's are used in stage lighting up to a certain
wattage as their arc sizes are still about the size of a comparable xenon
lamp, and they have operational advantages over xenon. But once you get
up to talking about a lamp in the 1000 watt range for stage or spotlight
operation, or for film projection, you normally then have to go to the short
arc xenon to be able to get the same amount of light through a small
aperture, which is what will give you the tight collimation that you probably
want. If you just want to flood a very large area with light, then the HMI
may very well be suitable, and probably more cost effective. But you won't
be able to focus it down very small, strictly a floodlight application.
Doug
Doug Dulmage
> I remember asking a couple searchlight operators years ago what they
>used, and they told me not only xenon (one said mercury-xenon, although
>since then I have seen only pure xenon spectra), but the wattage. I
>somewhat remember those trucks with 4 searchlights on them have either a
>500 watt or a 1,000 watt lamp in each individual light.
Well, the original old army searchlights were all carbon arc, and they were
also used in follow spots and film projectors until the invention of the short
arc xenon that had the proper color temp. As for the 4 lamp Skytrackers(tm)
that you're thinking about, they use a little bit larger lamp. Those typically
run with either a 7k or 10k (thousand watt) xenon lamp. I have seen some
smaller models used, but even then they are still around 4 thousand watt.
A typical cineplex theater lamphouse will use at least a 2.4kw xenon
just for lighting up a 30ft screen, so you can see why they need to use such
a large lamp to light up the clouds at 2000ft or so. Thanks to newer switching
power supplies, you no longer have to carry around a 3 phase silenced
generator to run such a large lamp, most theaters running up to a 2.4k lamp
run them off of single phase 220 volts with a supply that one person can
carry. They used to be all big iron transformer units that took a crew of four
to lift, so they can pretty much build the power supplies for those 4 lamp
units right into the trailer, and then run it from a much smaller and quieter
generator, or local building power.
Doug
Don Klipstein
Sven Hegewisch <Sven.He...@Physik.Uni-Muenchen.DE> wrote:
>>
>>
>>Scattering on small particles goes up with the 4th power of frequency,
>>so I believe that IR would be better for fog penetration.
>>( Long ago yellow light was used for "fog lamps" ).
Fog particles are so large compared to wavelength that they scatter all
"optical band" radiation nearly equally.
Ability to see illuminated objects through fog may vary with wavelength
for another reason: Photopic vision emphasizes sharpness and color, while
scotopic vision is lower resolution, monochrome, and designed to see light
where light is dimmer. In conditions where both are working, photopic
vision is better for seeing objects through fog while scotopic vision may
prefer to see the illuminated fog.
Scotopic vision is favored by wavelengths from mid-blue to mid-green and
peaks at 508 nmm or so (bluish green). Photopic vision is favored over
scotopic by wavelengths from yellow-green through red.
And some particular blue wavelengths have high "color impact" while not
stimulating scotopic vision a lot - this is the general 430-445 nm range,
including the 435.8 nm line of mercury. Mercury has earned a bit of a
reputation for seeing through fog, by lacking wavelengths between 436 and
546 nm. Although such blue wavelengths will often be imaged out of focus
by human eyes focusing on longer wavelengths - violetish blue can look
blurry.
- Don Klipstein (d...@misty.com)