A little bit about light

I’ve been giving myself a crash course refresher on light over the last new months. It started when I picked up a used Laser Cutter and wanted to figure out how it cuts with light. What I’ve written here is my understanding of things. I may be wrong, if so, please let me know in the comments.

My simplification of a CO2 laser is that it’s a poorly designed Neon light that gets way too hot and produces a heat ray that we can manipulate with mirrors to vaporize things. Magnifying lens on a sunny day style. I fear if I ever find an ant in my laser cutter whatever project I was working on will be a total loss as I will be chasing the ant with my laser beam. https://en.wikipedia.org/wiki/Carbon_dioxide_laser

So I now have this really sharp cut thing that I can’t see the blade on. A CO2 laser beam is invisible. If you see a red dot on a laser cutter, that is a separate cat-toy style red laser put in place so we can guess about where the actual invisible laser will do it’s thing.

Deep Infrared thermal image of laser cutting fabric
The heat line produced by laser cutting some fabric in a laser cutter
laser cutting fabric
The laser cut fabric. You can see where it has cut the fabric using focused invisible light.

My laser cutter’s light is 9.4-10.6 micron wavelength. This is the same wavelength that Humans glow in the dark. Well, everything room temperature glows at this light frequency or ‘color’.

Deep Infrared

A thermal camera can see light in this ‘Deep Infrared’ zone. I have a Seek Thermal camera that plugs into my cell phone which allows me to see effectively heat. I can walk around and find things that are plugged in that are doing a bad job of being off, and give off heat because they are still on. I can tell the temperature of anything, just by looking at it with my cell phone. I can also look for things that are supposed to help keep me warm and are failing at their job like doors and windows.

A Deep Infrared image of a Kurig Coffee Machine
A Kurig Coffee Machine that wasn’t told to ‘power save’. It’s been heating up since it was plugged in.

Except nothing is ever that simple. Materials have a property called ‘emissivity’. This is how well they emit light at a certain wavelength. Things that emit light well, tend to absorb light well. Things that don’t emit well tend to be reflective in nature.

Humans have a pretty high emissivity about .98 (with 1 being perfectly emissive and 0 being perfectly not-emissive) so we need clothes to stay warm as we would glow all of our heat away without them. But because we are highly emissive, we can absorb heat well too, so this is why you can feel heat being given off by things like hot pans, light bulbs, and turtle heat lamps, and sitting in a sunny spot.

You can see here that I glow. My clothes hold in some of my heat and my glasses block the Deep Infrared light.
You can see here that I glow. My clothes hold in some of my heat and my glasses block the Deep Infrared light.

Things such as shiny metals have a low emissivity, so they tend to reflect heat like a mirror. This is how camping space blankets work. The thermal ‘glow’ that us humans have gets reflected back at us. We absorb a lot of this reflected heat, so space blankets feel warm to us. Because, you know, science and stuff.

But, what this means, is that my fancy thermal camera can’t take accurate temperatures of shiny metal things. What I am really taking the temperature of is the things reflected on these ‘heat mirrors’. To do a good job using thermal imaging for temperature reading the more expensive equipment has material tables that you can assign to spots that have a lookup to a emissivity table so it can calculate the proper temperature based on what it sees.

I am going to carry some electrical tape which has a pretty high emissivity number around .96 and just stick that on things I want a proper temperature of. Because, you know, lazy and stuff.

Materials have some pretty funny ideas about what is ‘clear’ and what is ‘opaque’ at wavelengths other than what we can see with our eyes. Thin plastic bags that we can’t see through are transparent to deep infrared. Stick your hand in a bag, you can see your fingers as clearly as if the bag wasn’t there. Windows, glasses, things that we see through all the time are as black as night to thermal. “Low E” windows are not only black to thermal, they are reflective as well, so you can see your heat reflection in a ‘good’ modern window. CLICK. OH, that’s why “Low E” windows are better, they reflect heat. I get it now.

Near Infrared

Another portion of light, called Near Infrared, has some interesting properties as well. First off, things that aren’t metallic (reflective) are rather transparent. Things look kinda like jello at these wavelengths, the light can see into them a ways. A couple of centimeters often times.

The Near Infrared has another interesting ability. Oils, fats, sugars, alcohols, and proteins absorb certain frequencies of light – they have colors (for lack of a better word) in this range. Click here to Geek Out on Near Infrared. This means that a camera that uses Near Infrared is very useful around the house. We can look at something, and judging by it’s ‘color’ in Near Infrared, we can make a good guess as to what is made of, or at least major components of it. We can’t see near infrared, so we tend not to manipulate the colors in that range.

There is a gadget that takes advantage of these useful properties. The SCiO which is a Near Infrared ‘scanner’.

This little device is even cooler than the thermal camera. It’s small, and can tell you the interesting bits about your food like how many calories and of what type (fats, carbs, protein) are in it. You don’t have to guess at a restaurant if you are tracking your diet anymore.

This doesn’t work like a camera, it is instead a spectrograph. It doesn’t take a picture of stuff, it instead looks at all the colors that are present like how a prism works. You scan something with a SCiO and it breaks apart the intensities/brightness of different wavelengths of light (those would be the colors if this was visible light) and looks up what it sees against a database of stuff that it knows about and when it finds a match, tells you what it is looking at.
If we were to present only pure substances it would be able to tell us what things are easily. However, we don’t have much of anything that is truly pure. Table salt, sugar, baking soda, for the most part tap water are about all I can think of commonly around the house. Most of the stuff we interact with is made up of a variety of things.

This is where we get clever with the SCiO. Instead of needing to extract out the stuff into individual bits (imaging taking a baked cake and separate it back out to it’s flour, sugar, eggs, milk, water, etc) we just capture what a thing looks like in different bits of Near Infrared light and correlate it to things we’ve told the SCiO what they are previously.

The thing that makes this work is that we LIMIT THE DOMAIN of what things are so the SCiO has a chance at making a reasonable guess. For example, there are a lot of things that are Red. Lego, fancy cars, strawberries, some apples, etc. If we showed you a particular shade of red, and asked you what was that color, you can come up with a lot of wrong answers that are that exact shade of red. But if we said we have a berry that is this particular color, you would be able to tell very easily what it is most of the time. Especially if you can look back against other color samples and compare what you have now with what you have seen in the past.

So for the SCiO to work well, we need to train it. We get together a bunch of things that we want to tell apart if it’s not properly labeled. We then teach the SCiO this thing is X, that thing is Y. We can than ask SCiO what is this stuff, it’s something that belongs to this group that we trained it on.

An example could be clear liquids. Clean water, vodka, strong vodka, watered down vodka, rubbing alcohol, denatured alcohol, clear soda, vinegar. These things all look similar to our eyes. They will all look different from each other in Near Infrared. We can train the SCiO about all of these clear liquids, and when we find a glass of one and we don’t know what it is, we can check with the SCiO.

Amazing!

There are some ways in which the SCiO can fail.

  • Shiny mirror like surfaces tend to reflect all light, regardless of the wavelength. Metals for example. We also see this in Visible light as well as Deep Infrared.
  • Things that are black – they absorb light – tend to absorb all frequencies of light including Near Infrared. Things that have been colored black will likely be black to the SCiO as well, and it can’t get a good read on them.
  • Only the major components of something can be read by a SCiO. If there isn’t enough of something to make a strong ‘color’ influence, it simply can’t be read. A SCiO can ‘see’ stuff that is more than 1% or so of the overall item.

 

Understanding how a fancy new tool works ‘under the hood’ helps me manage my expectations of what the tool can and can’t do well. I can ‘hack around the edges’ of it’s capabilities because I understand what the edges of capabilities are and why they exist.

Anybody else try the SOL Escape Bivy? I found one on clearance for $35 shipped and…

Anybody else try the SOL Escape Bivy? I found one on clearance for $35 shipped and thought I'd give it a try. $50 is too rich for my blood given the mixed reviews and stories how it's a tight fit. Only been wanting one for 2 years.

The features I liked in the ads are the unobtrusive green color, heat reflective construction, and waterproof while being breathable.

I ran it through it's paces as best as I can with the temps running around 0 outside.

Initial test. I filled the stuff sack with water. The sack is made of the same material, without the nicer seams. The water poured out the seems, but no seeping on the main material. Sticking your hand in the bag, you do feel the 'space blanket' effect with nearly instantly warmer hands.

First night I climbed in it in bed, and tossed my usual quilt and wool blanket over me and the bag. I felt decidedly warmer than usual even with lots of skin contact to the bag. In the morning there was no clamminess so the breath-ability claim is substantiated in my book. If it didn't breath, I should have been swimming like a fish.

For the 2nd night, I decided to 'camp out' in my basement with my oldest 2 girls. The basement runs mid 60s during the winter. I rigged up a pair of hammocks for my girls out of bed sheets and lots of blankets. 
I slept in a hammock and the bivy wearing sweatpants and a tshirt. I froze! My trip out in 3 degree weather and strong winds in  down bags had me less chilled (although much colder in spots) than 65 degrees with this bivy. 3 am, I folded and grabbed my light down jacket and wool hat. Covering my torso and arms and I slept great the rest of the night.

This again confirms what I've known for a while. Space blankets need space in order to work. This bag is SO tight on me that I doubt I can get my summer weight down bag and myself stuffed inside. Warm thin clothes is the best I can hope for.

I think I may modify the bag by adding a heavy space blanket diamond to the bottom. Slit the bag about 3 feet and tape in a diamond shaped patch maybe 6 inches wide. I am going to try to seal the stuff sack with some Gorilla brand clear repair tape to see how well it sticks and durability before I cut the bag.

This isn't a down bag, for sure. I don't foresee any use for this in cold weather. It is also not a comfortable bag. Given the size and weight, it will be my ultralight summer setup. I will be using this bag a lot I expect simply because it's so svelte. Cowboy camping in my future in this bag for sure!

Anybody else try this bag?

In album 2015-02-22

244 grams for a waterproof bivy/sleeping bag seems like a great way to go ultralight.

Shiny on the inside. Supposed to reflect radiant heat back at you. As long as you don’t touch it.

Overnight in the hammock hung in the basement, 63-65f, and I froze wearing sweatpants and a tshirt. 3am I had to get my down jacket and a wool hat, and then I was good the rest of the night.

Some nice details such as nice finished seems on the inside, and a dart at the end of the 1/4 length zipper. Six foot four 235lbs for 2 nights really pushes out on the bag and the seems only settled a little bit.

I rigged up a pair of bedsheet hammocks for the girls, tied off the treadmill. They enjoyed it OK. Not a fan of the hammock yet. Practicing camping with them so they do better when we go for real.

There is something about being on the Ice Age Trail in single degree weather

Wife sent me packing with a buddy for my birthday. I think she started a dangerous precedent.

43 lbs missed the ultra light mark by a shade but that had food for a week, not two days. A pound of summer sausage weighs a pound. Who knew?

I was packing for -7f. Clouds rolled in last minute and it only got down to 3. But windy! Likely negative teens to twentys windchill in a hammock without one of those nice wrap around tarps. In fact, my 'tarp' was a wool blanket.

I fell in love with bits of my gear and learned to trust it better.

I got cold, but never froze. My buddy with twice the weight froze his butt off. He was cold for a full week after the trip.

Oh, the unexpected clouds? I drove home into a blizzard. #irony

In album 2/20/15

Yes, that is cast iron in the middle. Gotta hang onto that friend that is willing to pack cast iron!

Hanging out on a ridge between two lakes.

I need to practice my photo spheres.

This just looks cold.

I decided to 'fix' a blanket I got from freecycle

It is a military wool blanket. I love wool blankets for camping and hanging out outdoors. I don't much care for the olive green – even though green is my favorite color.
So I dyed one side of if grey. I couldn't find anybody else online (just a short search) that dyes a single side of a blanket. So I made it up as I went along. I'd picked up some Dharma Trading 'Twilight grey' and basically painted it on for lack of better description. 
Normally you soak whatever you want to dye, but that will get the whole thing. So I mixed up the dye, water, vinegar (a mordant, helps the acid dye work) and a bit later, soap, for better 'wetting' of the blanket.
I am really, really impressed with how it turned out.

In album Dye single side of wool blanket

The green is still green, the grey, is a dark forest green.

Something I’ve done with the grey blanket is made it more water resistant.

water beaded up in the center, soaked in on the lower right.

I’d treated the grey blanket last year with lanolin. The oil that naturally occurs in wool while the sheep are wearing it, It’s what keeps sheep dry in the rain. In one context it seems silly that it’s taken out, but the wool can’t be dyed with it still in the fibers. So I add it back, and make the blanket more water resistant.

I am dying my green wool blanket grey.

I am spraying the dye on. I am using a spray bottle rescued from the recycling. It works just as good as the ones that cost $3 – probably because it did cost $3, but full, not empty.

I mixed up the dye, vinegar, and water into a juice container rescued from the recycling, and poured it in a little at a time with the funnel. The second batch I added a bit of dish soap to ‘wet’ the wool. The dye spray was beading on the fibers, the soap helps it soak deeper into the fabric.

The light grey in the upper right is the dye as sprayed on. I worked it into the blanket surface so I got better contact with the fibers instead of the spray just sitting on top of the blanket.

I want a mildly dappled effect, so I heavily dappled the blanket with the dye. It spreads out, so the effect is much more subtle when dried.

I hope…

In order to set the dye, I microwaved the blanket while it was still damp. I misted the dye side with the dye right before folding it dye side together and rolling it up. Microwave the daylights out of it in couple minute bursts.  I took it out, and re-rolled it with what was on the inside on the outside so I get even steaming of the dye.

I re-folded the blanket and nuked it some more. It was probably cooking a dozen 2 minute bursts.

I stuck it into a kidde pool to wash. This is the moment of truth… did the dye bind to the wool or will it leach out?

The water just barely tinted, so the dye fixed to the wool! YAY!

Hanging to dry. The color is better than I expected. I really like the dappled effect, very subtle.

The still-damp blanket in the house. I really really like the dappled effect on the folded blanket.