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Ben FrantzDale

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PSA [Jun. 26th, 2006|07:55 am]
Ben FrantzDale
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Compact fluorescents

Compact fluorescent lamps don't suck anymore. I had written them off after my parents got them when I was younger. At that time they weren't very white, flickered, and took a while to turn on. Today they don't seem to flicker, have a fairly good spectrum, and start up quickly. (They do get to about 80% instantly, it takes a minute to get to 100% but it's not too noticeable.) They also take about a quarter the power of a similarly-bright incandescent. By changing 300 W of lights in my primary room in my apartment, it should be the same heat effect as having more than two people leave the room. The glass globes on my overhead lights are now 109° F rather than 131° F with 100 W incandescents.

I was thinking of this in terms of keeping cool in an apartment with no AC, but the cost savings, at least, should be even better with AC. It looks like an average AC unit does about 2.5 watts of cooling for each watt of power you put in, so replacing a 100-watt bulb with a 25-watt one should result in a savings of 75 W + (75 W/2.5) = 105 W – that's more than the bulb itself. (Note: I am not a HVAC specialist.)


In completely unrelated musings, good old Gaussian blur is not the same as out-of-focus. Whereas Gaussian blur is convolution by a normal-distribution–shaped kernel, the blur you see in a camera is convolution by the camera's aperture, creating artful roundish dapples of light. After a discussion on Wikipedia's Talk:Gaussian blur, The result is apparently called bokeh. You wind up with bright circles (or hexagons or octagons) where bright points are out of focus. There's a GIMP plugin to do all this which works nicely. Still, doing it by hand I was able to go from

to .


In still more unrelated news, the Linux equivalent of Spotlight and Google Desktop Search, Beagle, Just Works with Ubuntu if you install it. Between this and alpha-blended windows with drop shadow, the look and feel of my home Linux box has caught up in major ways with Mac OS X.

[User Picture]From: thegreatgonz
2006-06-26 01:23 pm (UTC)
There's a lot more to bokeh than convolution with a kernel, whatever the shape. The Wikipedia link mentions this image, which shows one of the complications- the shape of the Bokeh varies with position on the image plane, particularly away from the centerline. It's not even a predictable planar distortion- look down near the girl's stomach. It's determined by the 3D geometry of the camera optics. Also, although it's hard to make out in that image, Bokeh often have an internal speckling structure, which is sometimes organized into rings (I described these effects in the context of human-eye bokeh from laser light here, although I didn't know the term bokeh at the time).

I know all this because someone in my lab is doing a research project on bokeh, to try to model them more effectively than is possible with the convolution-with-a-kernel model.
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[User Picture]From: benfrantzdale
2006-06-27 12:22 am (UTC)
Interesting. I'd be interested in seeing what this lab mate comes up with. (As for the laser topic, I asked it on Talk:Laser. We'll see what we get.)

I know the GIMP plugin can account (more or less) for blur from near objects obscuring far objects and far objects' blur cannot obstruct nearer objects. But as you said, it's more complicated than this. Experimenting with my SLR, a point light source, and my finger, it appears that when my finger is near the lens it modifies the aperture so the silhouette of my finger, reversed in x and y, is removed from the convolution kernel. I think this is what's causing the cut-off splotches in your first link.

On the SLR I did notice that the near splotches appeared dish-shaped (dimmer in the middle) whereas the far splotches were more even. This might be a flat-field issue; it's an inexpensive zoom lens.
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