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.

2nd layout of the Mobile Science Lab

I added more items to the Mobile Science Lab.  The main new item is a WeatherFlow WEATHERmeter. This is a pretty neat bluetooth device that captures wind speed and direction, temperature, humidity, and barometric pressure.

layout of pieces for the Mobile Science Lab
The Mobile Science Lab in the middle with the new WeatherFlow WEATHERmeter to the left along with a USB drive that works with cell phones. The new layout is on the right.

New stuff means I needed to update the case.  I fiddled a bit to get everything to fit.  I think the next iteration will end up including layers.  I will need to find some laser safe foam core or something light like that.  The cardboard won’t hold up all that well when there are removable sections.

trying to make cell phone accessories fit into a cell phone drybox
An initial cut of the new layout on some old cardboard that is scarred up from the laser cutter. I think it looks pretty neat this way.

I ordered a much larger Pelican case tonight. The SCiO I am ordering at the end of the week should fit into the new case.

I’ve also added some NFC stickers a few places to make using the bits a little easier. The case has my contact info embedded in it.  The WEATHERmeter is now set up to just tap the phone against it and the correct App will load.

cell phone accessories in a waterproof cell phone case.
The new layout is a lot more full than the previous version. You can see one of the NFC stickers on the lower left corner.

The miracle of having all the hobbies, is I tend to have lots of kit with me

My 5 year old picked up a splinter in her big toe.

My botany kit has some tweezers, a sharp knife, and a light on one of the tiny microscopes.

My essential oils travel kit has clove oil. A good topical anesthetic and antibacterial.

A dab of clove oil, a bit of digging around with the razer knife, and a pluck of the tweezers. No more splinter.

A look at the splinter, an explanation of the oil used, a wiff of lavender. A happy little girl.

I am at dreamforce

I've been attending non-core and small sessions so far to broaden my knowledge, as the big ones and keynotes will be available online. Over 8 miles of walking today my phone tells me. I packed light and carried the full week's stuff with me all day.

In album #DF15 Day One

dreamforce. I’ve been reading about it and watching the videos for the last couple of years. I am actually here, in San Francisco this year!

They knew I was coming, the soda selection? Top notch!

The top bag is my Kelty Oriole bag. I packed for the week in this bag. A little inspiration from my online Ultralight Backing Group. I knew I was getting a backpack at the event, so this works out for me, I have room for bringing stuff home in the 2nd bag.

I’d drive it to work lettered up without shame! Well, the ‘win me’ on the hood could be removed to clear up any confusion.

Talk about a surprise, seeing one of my machines at dreamforce for the Internet of Things Cloud booth. We could do oh-so much more to really show off everyone’s capabilities.

Powell street Trolly!

I have a trip on the calendar for the 4th of July for a trip with a buddy (who isn't…

I have a trip on the calendar for the 4th of July for a trip with a buddy (who isn't a ULer). My wife sent me to Aldi's for some ground beef, and I saw a few things I just had to have. A 40oz stainless water bottle and the Adventuridge Lightweight Foldable Backpack.

The backpack really reminded me of a small version of the G4 DIY ultralight bag. I've been meaning to make that bag for a few whiles. Just no time and a lack of ambition.

This bag is $10 and folds into itself. The back is padded, and the straps are double layer, but not padded. I figure I can rip open the seam, add my own padding, and sew it back up as good as new. Suggestions on a padded shoulder strap material?

There was also a black and red version. I picked this bright (like bright blue car bright) blue and silver one because I have some 'twilight grey' fabric dye I like to use to tone down bright articles. It should match my Kelty Hip Bag I posted here a few months ago.

I stuck it on the scale and it comes in at under 11oz or a touch over 300 grams. It claims 7.9 gallons which is 30 liters or 1825 cubic inches. A kids bag in size, really, but I suffer from fill-er-up-itis so a small bag is just what I need. I also have kids… so when I start going with them, they will have a bag to use as well.

I do plan on mating it to my Kelty hip bag with some clips so they function as a single bag. The Kelty is a great hip bag and will do the load bearing bit. This new bag is for the lighter stuff like the sleeping bag, hammock and such.

In album Aldi’s Ultralight backpack

This photo is pretty close to the true color of the light blue. It’s actually brighter yet to the eye than to the camera.

10 3/4 oz for a 7.9 gallon backpack. The best part? $10!

306 grams (including the cardboard tags). It folds up into itself nicely as well.

Turn it over, and you see it’s a backpack that really looks like that DIY G4 backpack I’ve seen plans for online. And it folds into itself so I can stash it nicely when I am not using it.

The outside is nice and simple. The over-flap has a zipper pocket like is very common. The color is very bright. Florescent lighting doesn’t really capture it.

The back is padded, but the straps aren’t really padded. I figure I can open up a seam, add some padding, and re-sew the seam on the straps.

I gave the brand new bag in a dye-dunk to try to tone the brightness down and make it more closely match my Kelty Oriele bag. The gray is a tad purplish, but this dye does that. I think a second round and I may have it tinted quite nicely to match. Also check out that big 40oz stainless water bottle for $5 at Aldi’s as well.

The hip pack has clips for shoulder straps. I plan on clipping the new bag onto the hip pack and using the hip pack like the waist belt. The heavy stuff can go into the lower bag, the light, bulky stuff can go in the new bag.