I recently gave a talk at Ames and got to see some of the vibration testing work they are doing.  I, however, did not get to see this.  You have got to love it when brilliant minds, like theirs, come up with beautifully elegant solutions to complex problems.

White light can be simulated by combining red, green, and blue light.  This is the method used by TVs, LCD screens, and compact florescent lights.  Could white LEDs be doing something similar?  Could they just be red, green, and blue diodes combined into one unit?  The simplest way to answer this question would be to google it, but let’s wait on that.  This gives us the perfect opportunity to do some empirical experimentation.  Let’s look at the light spectrum produced by a white LED.  To do this we need a spectroscope…or some cardboard and a CD.  There are multiple sites out there with instructions on building your own.  Here is a photo of the one I built.  You can find instructions to build a similar one here.  BTW: You can also use these spectroscopes to determine what gasses are used in your florescent lights – a topic for another time.

If the white LEDs were combining multiple colors to simulate white light, it would look something like the image below.  This image, by the way, is the spectrum of a typical compact florescent light.  You can see “bumps” in the image that represent individual wavelengths of light that compose the simulated white light.

However, this is not what you see when you look at a white LED.  Below is the image of the spectrum I captured from a common LED flashlight.  This is interesting!  ”Why?”, you may ask.  It is surprisingly continuous.  It seems to be composed mostly of a wide, smooth blue/green band and a wide, smooth red band.  There is practically no yellow though.  This seems to indicate that there are probably not three separate diodes in there, but the wideness and smoothness of the spectrum is a bit strange.

Another interesting aspect of this spectrum is that the red and blue ends look like they have a similar shape.  I’ve sketched this out in the plot below.  Now, I’ve hit a point where I need to google for answers.  After a quick search, I found that many white LEDs are actually blue LEDs that have been doped with phosphors that fluoresce red when exposed to blue light.  This explains the observation that the light was mostly composed of two similarly shaped blue and red spectra.  So there, a quick little experiment that taught us something about how LEDs work.

I visited the  La Brea Tar Pits today.  This was one of my “bucket list” items.  Ever since I was a kid, I’ve always heard about the excellent fossils found in the tar pits.  It was roughly a 30 minute drive to get there, which took me from one end of Los Angeles to the other.  Not a fan of LA driving/traffic.  I really hate the traffic and the reckless abandon with which many people seem to drive.  This little trip gave me the chance to get more practice on the freeways.  I’m calling it a learning experience.

Anyway, forgetting traffic for a while, the specimens they have on display at the museum are really amazing.  It’s hard to get a sense of the scale of this beast, but he is around 12 feet tall.  A truly massive creature.  The magnitude of the fossils is also astounding.  For instance, in this next picture are 404 dire wolf skulls…and that is ONLY the ones in this display.  There are many more.   As a matter of fact, the guy in the photo is actually composed entirely of dire wolf skulls, true story.  All in all, it was a worthwhile experience.

I haven’t really decided what is going to go here yet, but hopefully it will be something interesting…perhaps research related…perhaps not.  Regardless, I’ll try to keep the place up to date.

I recently moved across the country for work.  This might be a good place to document the experience of resettling.  We’ll just have to wait and see how this thing develops.