Products > Thermal Imaging

DIY SWIR/NIR source from a halogen lamp

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DaJMasta:
This forum has seen some SWIR and NIR threads, so I assume this is the best place to put it.  I designed a printable lamp housing for a reasonable power selectable band source made from a printed box, a tungsten halogen lamp, a longpass filter, and it seems to work well.  The box is sized and designed around a 10W, 12V halogen lamp - the heat output of halogens is high, so there are lots of ventilation slots, but they angle away from the front face with the filter, so a minimal amount of visible/out of band light will show on the front face target.  I used some reflectors found on ebay, but there is probably a good variety that will work, and reasonable gauge solid core wire makes for a reliable lamp mount that can be bent to focus against the reflector in back.  The optical filter can be selected for usage (a tungsten halogen lamp is a very broadband source), and is a standard 50x50x2.5mm size (2" square) that is often available on the used market.

https://www.thingiverse.com/thing:4758234



For the pictured box, I used a 2800k halogen lamp (lower color temperature means a larger portion of the total emission below the visible band), a reflector off ebay, and a Schott RG1000 filter (1000nm longpass).  The filter will likely be the majority of the cost of the whole thing.  I screwed on the reflector with M3 machine screws and nylon spacers, then I stripped the solid core wire and bent it approximately in place, securing in two places with zip ties, so that I could solder the lamp in place to the wires.  Then I made sure to clean the lamp with isopropyl alcohol, slid the filter into the front slot, and pressed the two lower halves together.  A couple of nuts and bolts, one on either side of the bottom, help keep the press fit parts hold the wires in place better, then you press fit the top piece on it.  The bottom has a 1/4" 20 TPI thread built in for a standard camera threaded mount.


(the room is much darker than the high gain of the visible camera makes it look)

The results are good!  You get stripes of unfiltered light facing to the side and back, but looking at the face of the light you only get what comes through the filter, I've got a set of cameras setup for multiband visualization and you can see that the RG1000 passes as expected - the NIR camera can see it in its reduced sensitivity region (sensitive to about 1150nm, I figure), whereas the SWIR camera sees a bright light.  You can see a tiny bit of UV through the slots, but I think being low color temperature and probably a standard glass lamp (rather than quartz glass), there is little UV emitted by the lamp used.

http://medpants.com/ee/SWIR%20Source%20SWIR%20only.jpg

(the plastic magnifying glass passes SWIR just fine!)

Fraser:
Nice project  :-+

Only one safety related comment though. Halogen lamps are well known for the high temperature at which they operate. Such is necessary for their correct operation to preserve the filament. As such care is needed when using Halogen lamps near plastics. My Tiertime UP! Box 3D printer uses fire retardant 3D printed parts for its extruder head covers because Tiertime warn that normal 3D ABS burns easily and is a potential fire risk. I know you are being careful and will not leave the lamp unattended whilst operating, but do keep an eye on it as if the top casing melts down into the Halogen lamp things could get ‘interesting’ .

Lamp houses for Halogen lamps used with Microscopes use metal, ceramic and heat resistant plastics, and for good reason.

Fraser

Ultrapurple:
That's an excellent piece of work, and a very useful design for the community.

Thank you also for posting images made at so many different wavebands. I see I'm not the only person who has LWIR-to-UV capability!

Bearing in mind what Fraser said, is it worth considering adding some simple thermal monitoring or protection in the housing (eg a resettable thermal fuse)?

DaJMasta:
Thermal fuse would be pretty easy to put up top, I left it going for a few hours and examined it with a thermal camera too as I figured that was the risk with it, and with a 10W bulb it seems to be fine - no softness or drooping in the top plastic and no obvious hotspots that are too high externally.  The center of the filter window has a similar hotspot, and as expected, the wires coming through the base of it, but at least provided that the lamp doesn't move from its set position it appears to be fine for operation at room temperature.  I wouldn't put it in a high vibration environment or anywhere particularly hot, though.

Aside from making it larger or having a thermal cutoff, I'm not sure what could be done to make it safer (I guess underdriving the lamp would do it too).  I had thought about looking for an IR reflective paint, as it may give a bit more output from the front window as well, but while I have the equipment to test paints for their performance, I don't know of ones that really advertise it and don't really feel like taking the time  ;) Too many other projects on the way.

bap2703:

--- Quote from: Fraser on February 11, 2021, 11:22:38 am ---Lamp houses for Halogen lamps used with Microscopes use metal, ceramic and heat resistant plastics, and for good reason.

--- End quote ---

Got one just next to me:


Interestingly the lamp is encased in a metal shield.
The vents are only there to cool the casing, but no external air flow is hitting the lamp itself.
That might also help with the temperature stability of the lamp .

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