Blinded by the light (slight return)

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Discussion Overview

The discussion revolves around the photography of various light sources, including halogen bulbs, arc lamps, and lasers. Participants share their experiences capturing images of these sources and the complexities involved in the process, including technical challenges and the visual characteristics of the light produced.

Discussion Character

  • Exploratory
  • Technical explanation
  • Experimental/applied

Main Points Raised

  • One participant describes the process of photographing a 12V 100W halogen bulb, noting the technique of combining images of the lit and unlit bulb to capture the filament's appearance.
  • Another participant shares their experience photographing a high-pressure mercury arc lamp, detailing the steps taken to capture the startup process and the thermal expansion of the electrodes.
  • There are mentions of the ethereal quality of images taken with a germicidal lamp, with one participant comparing the visuals to ion thrusters tested at NASA.
  • A participant expresses uncertainty about the compelling nature of images taken of a NeHe laser and a medium-pressure Hg arc lamp, while also noting the presence of fringes in the initial startup light that may indicate density variations.
  • One participant observes a color change in the images of the arc lamp, suggesting it might be related to the UV content of the light, but admits uncertainty about the cause.

Areas of Agreement / Disagreement

The discussion includes multiple viewpoints and observations regarding the photography of light sources, with no consensus reached on the compelling nature of the images or the reasons behind certain visual phenomena.

Contextual Notes

Participants express uncertainty about the interpretation of visual effects, such as color changes and fringe patterns, and acknowledge the technical challenges involved in capturing these images.

Andy Resnick
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For whatever reason, the "blinded by the light" contest has stuck in my head, motivating me to take some images of sources.

As usual, don't try this at home.

Halogen (incandescent) bulbs are fairly easy to photograph: this is a standard 12V 100W bulb

[PLAIN]http://img713.imageshack.us/img713/1043/hibeams.jpg

This was done by adding together an image of the unlit bulb with an image of the lit bulb- that's why the reflected filament is cold metal. Easy breezy.

More interesting are arc lamps- I have a spare 100W Hg high-pressure arc, so I thought it would be interesting to get some images while it was firing. Here's the unlit bulb-

[PLAIN]http://img141.imageshack.us/img141/3287/unlit.jpg

The gap is about 1 mm, and somewhere inside is about 100 ug of Hg. There's other gases as well. After taking this image, I stopped down the lens to about f/120, set my shutter speed to 1/640 s, turned on the bulb and started snapping away, decreasing the shutter speed all the way down to 1/8000 s as the bulb came on- the process took about 20 seconds. After it was lit for a few minutes, I increased the shutter back to 1/60s and turned off the bulb to take an image of the hot electrodes.

I've never seen images of this process. Arc lamps are fairly complex to understand, but it appears that there is a multicolored diffuse glow from the other gases present, which heats up the Hg. The diffuse glow then goes away, and as the Hg heats up, it pools and collects in the glass as it evaporates, finally resulting in a concentrated arc.

The cooldown image clearly shows the thermal expansion of the electrodes.

[PLAIN]http://img197.imageshack.us/img197/8607/startup1.jpg

[PLAIN]http://img141.imageshack.us/img141/9681/startup2.jpg

[PLAIN]http://img441.imageshack.us/img441/4006/startup5.jpg

[PLAIN]http://img715.imageshack.us/img715/8358/startup8.jpg

[PLAIN]http://img251.imageshack.us/img251/4813/lits.jpg

[PLAIN]http://img703.imageshack.us/img703/6186/cooldown.jpg

The other sources I want to try next are a HeNe laser (which I have to disassemble first) and a 1200W medium-pressure Hg arc we use for lithography. The laser should be straightforward, but the MP arc may be problematic due to the excessive amount of UV light. Stay tuned...
 
Last edited by a moderator:
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Wow great pics Andy
 
Sweet!
 
Thanks, guys.

While procrastinating putting together a talk for Friday, I remembered I have a germicidal lamp in the culture hood, so I figured I'd 'warm up' with that before trying the Mother Of All Fluorescent Lamps.

It wasn't pretty to get these- if I walked in on my student doing what I was doing, I'd be really p-ssed and kick them out with prejudice. Can't say I love these, but there's an ethereal quality that is interesting- it reminds me of the ion thrusters they build and test at NASA GRC.

[PLAIN]http://img826.imageshack.us/img826/8961/lit2.jpg

[PLAIN]http://img842.imageshack.us/img842/5458/lit1.jpg

There's some sort of contraption inside the ring, but I couldn't get the angle to clearly see it. As it was, I practically had to climb inside the hood to aim and focus.
 
Last edited by a moderator:
Very cool pix!
 
As promised, here are some images of a NeHe laser and a medium-pressure Hg arc lamp. I dunno, there's nothing really compelling about these...

Here's the laser tube; a couple different views showing the laser cavity (the thin magenta capillary):

[PLAIN]http://img24.imageshack.us/img24/8058/resultofdsc4056.jpg

[PLAIN]http://img254.imageshack.us/img254/320/resultofdsc4050.jpg

I set up a Michaelson interferometer to take some obligatory magazine-style photos, but the ones I have are boring.

Finally the Hg arc- the electrodes are about 100mm apart. Here's the unlit bulb (actually, the 'cooldown' pic so you can see the electrodes a little easier)

[PLAIN]http://img440.imageshack.us/img440/6186/cooldown.jpg

The initial startup light has a lot of fringes- I don't know if they are density variations or something else, but they are real.

[PLAIN]http://img338.imageshack.us/img338/4333/dsc4118.jpg

And as the arc comes up, it looks like this:

[PLAIN]http://img824.imageshack.us/img824/8607/startup1.jpg

[PLAIN]http://img525.imageshack.us/img525/6327/lit1r.jpg

[PLAIN]http://img141.imageshack.us/img141/8679/startup3.jpg

Something odd- if I let the camera set for a few seconds, the first image showed a definite blue tint, but images acquired immediately after showed the arc getting brighter and green (the change between images #2 and 3). I suspect this has to do with the UV content of the light, but I have no idea.

Enough of this... time to get back to work...
 
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