Light Test

The Light Test is among the many tests people use to evaluate outerwear.

One of the ways people often estimate the comparative density and wind resistance of fabrics is what is often called The Light Test ... observing how much light can pass through different fabrics.

One of our customers teaches Materials Science at a prestigious university, and I asked him what he thinks of the Light Test. Part of his response really surprised me. He checked with another instructor at the university, who had been employed by one of the biggest outdoor-clothing companies. She said her former employer relied on The Breath Test ... hold the garment or fabric against your mouth and feel how much air you can push through by exhaling. So I guess we need to do a Breath Test ...

The Light Test is really simple and widely used and can be instructive. But it's easy to be misled. Basically, the thing to keep in mind is that you must compare similar colors because color strongly affects the test results.

Partly because we are fortunate to have many readers for whom American-style English is not their native language, it might be useful to try to make clear the ways Americans use the words "light" and "dark".

LIGHT can mean:

• That portion of the electromagnetic spectrum that people see
• The color of an object that reflects a relatively large portion of the spectrum to which the human eye is sensitive
• The opposite of heavy (irrelevant to this discussion)!

DARK:

• A relative lack of radiation to which our eyes are sensitive
• The color of an object that absorbs a relatively large portion of the spectrum that we can see

Sorry if that was tedious, but it seems to me English is full of confusing usages!

It was a customer phone call that led me (Ralph) to create this page, and then to get Denali to do some controlled testing and photograph the results.

A customer called to tell me he'd just received a new Lynx Pattern All-Around Jacket, and done a Light Test against his FullWeight Drab CPO Shirt. He was surprised that the new Lynx let significantly more light pass thru than did the Drab. This result also surprised me, but I did remember observing the same.

I was surprised because the FullWeight Lynx Pattern had the same weight (density) and same wind-resistance properties as the FullWeight Drab. We do everything we can to make all our FullWeight Fabrics to the same specs, except for color. And we do the same for both our MidWeight Fabrics. So I didn't understand at first why Lynx would allow more light to pass through.

And this explanation is a little funny because it relies on people understanding the contextual differences in the way the words "light" and "dark" are used ... that's the reason for the bullet points above.

Compared to "dark" colors, "light" colors reflect more light waves. Our FullWeight Lynx Pattern and Black (and Drab and Duff) Fabrics are made from the same fiber, spun into Yarn with the same specs, and woven into Fabric with the same specs. But the light-testing our Black and Lynx Fabrics shows that Black Fabric will absorb far more light than will the Lynx, making some people think Black will stop more wind.

Black is black because it absorbs all the different colors of light waves. That, I think, is actually the definition of black. Lynx has four different colors, all of which are lighter than black, and one of which is undyed wool, which is quite light in color. Lynx is a lighter color because it reflects many different color light waves. And so when Black and Lynx are compared side-by-side in a light-absorption test, Black will absorb far more light than Lynx. This may lead people to conclude that the Black is a tighter weave, or that Black might stop more wind than Lynx. But it won't. I think the light test only tells you about light. Or maybe the light test is only indicative if you compare the same color.

The idea behind the light test is that the more fibers, the more light will be blocked. But I don't think "blocking" is all that is happening. Light colors reflect light waves. So I think the light waves bounce around within the light-colored fibers of light-colored fabric, and eventually find their way completely through the light color fabric ... not because they have encountered fewer fibers, but because the light fibers reflect the light waves and many light waves makes it all the way through the fiber. It is my guess that the light fabric looks light from the opposite side of the light source test is the same reason it looks light from the same side of the light source. Light colors reflect light waves.

The Black Fabric has sort of the opposite result. The light waves hitting the Black Fabric will encounter the same amount of wool, but the black color will cause the fibers to absorb (rather than reflect) much more of the light waves, with the result that far fewer light finds it way through the Black Fabric.

With luck, somebody who reads this will understand better than me and help me clean this up ... or maybe tell me I'm all wrong!

Here are some Light Test photographs from Denali, who photographed a light-check card in each photograph. The room was brightly lit for all photos, but half the photos had added backlighting. All of the images were photographed with identical camera setting. The only thing variable is whether the Tungsten Backlighting is on or off. None of the lights physically move, so light falloff over distance is taken out of the equation. 

The first pair of tests show our FullWeight Black Fabric. Kind of amazingly (or maybe not!), the Black looks the same whether or not it is backlit. The backlit image does not show any light at all coming through the Fabric.

Next, the same pair of images for FullWeight Lynx Pattern Fabric:

The Lynx looks very different ... the light colored parts of the pattern appear much brighter/whiter/lighter, and even the darker colors in the pattern are much lighter and kind of orange. Denali said this was caused by the Orange-Tungsten lamp used for the backlighting.

As mentioned, we do everything we can to ensure that our Black FullWeight and Lynx FullWeight Fabrics differ only in color.

We don't do a lot of knitting, but we do offer knitted Reversible Watch Caps and Neck Gaiters, and so Denali repeated the experiment with our knitted Neck Gaiters. The fibers are from the same sheep, processed in identical methods, knitted in identical patterns on the same machine, but the black stops all light, while the natural color (cream color) wool allows a significant amount of light through.

Black looks the same. All the light is absorbed by the dark color yarn, whether lit from the front only or from the front and the back.

And the Natural Color Yarn is MUCH brighter because a huge amount of the backlighting finds its way through the white (light color!) knit.

 

2 May 2023 --- Ralph and Denali