Testing UV absorption eyewear and sunscreen with a deuterium light source--make money online

today on Applied Science we're going to

talk about ultraviolet light I'm going

to test different ultraviolet safety

glasses and different kinds of sunscreen

to see how effective they are and we'll

try to answer the age-old question can

you get sunburned through glass in

addition if you want to find a material

that passes ultraviolet light we'll

check out some different options for

that for example if you're making screen

printing masks and to do all this we're

going to use this cool deuterium light

source and a spectrometer so let's start

with the deuterium light source in order

to do experiments with ultraviolet

absorption we'd like to have a light

source that is really broadband in other

words it has a very smooth output across

all the different wavelengths we want to

study you've probably seen these color

output charts for fluorescent tubes and

they look very spiky in other words

there's a really high peak in one color

and then there's not very much output

until you get to the next color and so

on but this is not helpful for us if we

want to measure how much light material

is going to absorb like for example

safety glasses or sunscreen so these

deuterium light sources are specifically

made to have nice smooth broadband

output into very far into the

ultraviolet spectrum the deuterium lamp

itself has actually built fairly

similarly to an ordinary fluorescent

tube it has four leads just like having

two pins on either side of a fluorescent

tube and it has a heater in there that's

for two of the leads and the heater is

just to make it easier to start the arc

it's a low pressure discharge lamp and

normally you could probably start the

arc in other ways but using a heater is

pretty easy so when you turn the power

supply on it warms up for about five or

ten seconds and then when the power

supply detects that the arc has struck

it turns the heater off very similar to

a standard old-fashioned fluorescent

ballast the reason to use deuterium in

the first place is because it has this

really smooth broadband output in UV and

the reason is pretty interesting for the

most part the emission is similar to

hydrogen as you'd expect but hydrogen is

easier to ionize than deuterium is which

means that more of the

energy that you put into it is going to

go into the emission lines that are

characteristic of hydrogen but as I said

earlier we don't want these emission

lines what we want is a nice broadband

output so with deuterium more of the

energy that you put into it comes out as

this very continuous molecular emission

spectra which is like a complicated way

of saying it but you you can change the

energy state of the molecule and it can

output it any sort of energy level at

once it doesn't have to be a specific

atomic emission I'll put a link to

Wikipedia if you want to hear more about

this okay so we've got our deuterium

lamp fired up and running stabili it

even has this little baffled light cover

here and the output is on this side

there's a couple of lenses to collimate

the beam somewhat and we're shining it

into the end of a quartz fiber and the

quartz fiber runs over there in this

blue jacket into the spectrometer and

then we'll read it out on the computer

screen and the idea here is that we can

put things between the light source and

the input to the spectrometer and then

check to see how the output changes okay

let's start with a baseline reading with

nothing between the fiber and the light

source so you can see here that the live

trace is in black so if I put my hand

here you can see the black trace goes

away and you can see the reference

colors here just to get an idea of how

far into the UV we're going so 400 is

typically the bluest light that you can

sort of see and then we're going all the

way to 200 nanometers with this

deuterium light source for a reference I

also put in a trace from an overcast day

aiming up at the sky and a trace from a

very sunny day also aiming up at the sky

so you can see that the Sun is of course

much much brighter than this light

source even measured a few centimeters

away but the light source has way more

deep ultraviolet light so for these

ultraviolet absorption measurements

we're going to make it's actually going

to be much easier to use this deuterium

lamp than even the Sun itself so I'm

going to clear the traces from the

sunlight and I'm going to change

the exposure time to be the 30

milliseconds so that we can get better

dynamic range and I'm going to set the

number of scans that we're going to

average lower because we don't need to

worry about it the deuterium lamp

actually does flicker so at the shorter

exposure time of just 4 milliseconds in

order to make it comparable to sunlight

I'd have to do a lot of averaging of

scans to keep the trace from jumping

around so let's say 30 milliseconds is

good this will give us good dynamic

range and then I'll also change the

scale so that we can zoom in on just the

part of the spectrum that we want to see

so now if we take a piece of ordinary

window glass and just put the glass

between the probe and the light source

you can see that there's a huge amount

of you ultraviolet absorption it is true

that pretty much everything below 300 is

is almost gone and you can see the

response is pretty quick so we could use

this set up sort of qualitatively and

just say oh ok glass is good to you know

320 nanometers and then I've got another

material here this is actually a plastic

knife disposable knife that one has a

little bit more UV cuts off it may be

280 or 290 but it would be nicer if we

could say in terms of percent how much

light is getting through for a given

wavelength so we can set up the machine

to do this or the spectrometer to do

this what we'll do is save the waveform

that we're currently looking at and then

request this transmittance profile and

then for some reason it changes the axes

a bit again so to set this back to what

I want we're gonna look between 200 and

600 nanometers and the output is going

to be in percent and I've selected a

hundred and twenty percent so that you

can kind of more easily see the hundred

so we'll set this to run and of course

everything is a hundred percent now

because that was the reference waveform

that we just got and I'm going to turn

off the color bar that's a little

distracting now if we take the window

glass and put it back into the profile

this is reading off in percent getting

through the window glass

pretty convenient and if we left click

somewhere we can see the exact percent

number as this y-value so at 349 a

meters window-glass

passes about 64% down here in the lower

range so let's say right at 300 we're

only getting 0.1 or 0.2 percent at 300

nanometers and then just to make sure

the system is working kind of the way we

would expect if I take a piece of metal

which should not pass any ultraviolet

light we can see that their reading is

pretty darn close to zero if I hang here

it's it's way down in the noise so with

the window glass if we're reading oops

if we're reading 0.2 that actually seems

like a real value if a piece of metal

only reads point zero two so this point

two percent seems like a real value at

300 okay let's try the first pair of

safety glasses these are ultraviolet

safety glasses sold with UV q adhesive

from Amazon and there are pretty generic

I couldn't find any brand name or any

sort of a model number or anything on

there so we'll put those in and you can

see that they do a very good job of

cutting out certainly 300 nanometer

wavelength light at 350 it's like 0.1%

or something at 405 which is actually

the wavelength that you would be using

your UV cured he civ most likely they

only let through 1% or so this next pair

of goggles came with my 450 nanometer

laser cutter a little desktop laser

cutter put this one on there

interestingly this one actually allows

through some ultraviolet light at around

three hundred eighty eight nanometers

still far down here it's quite low 0.2%

and finally these are safety glasses not

meant to protect you from ultraviolet

but they are meant to protect you from

Ruby laser light so let's just put this

in here just to see what the effect of

having of using the

wrong safety glasses might be and as you

can see these actually let through a ton

of ultraviolet light in fact at now 365

nanometer it's letting through 65% of

the light about and even at 322 it's

still appreciable at 4 or 5 percent I'm

going to run through some other

materials and it's pretty much the same

process for each one so I'll just show

you the results at the end this is

PMMA or acrylic

you

and now let's try some unusual materials

these are made to block ultraviolet

light from getting into a photopolymer

tank so if you have one of these 3d

printers that uses light to cure the

resin it uses the wavelength 405

nanometer and the trick is you can't

make you want to block all that light

from getting into the Machine or getting

to the resin so all the tanks are made

out of this special material that blocks

ultraviolet so let's test how good it is

so we noticed that the green material is

actually better at stopping 405

nanometers than the orange material used

in this 3d printer system so as a sanity

check I wanted to test it out with my

405 nanometer laser pointer so I've got

a fluorescent material here the laser

itself is purple hopefully this is

showing up on the on the camera and when

I hit the phosphor it turns green so if

I shine the laser through the little bit

of orange material check out what

happens there's still quite a bit of 405

getting through because the phosphor is

turning green right so the laser is

purple the material is orange but when I

shine through we're getting the effect

from the phosphor let's try the same

thing with the green material it's kind

of dark green we shine through there's

almost nothing I can't see any any

phosphorescence going on there at all

and see there's there's the laser so it

does an amazingly better job of blocking

405 nanometer at least not really UV but

405 just something to keep in mind if

you're ever designing a system where you

want to keep 405 nanometers out choose

the green material and finally I'm going

to test this vellum which I used in the

screen printing video the challenge here

is that the vellum is not transparent so

all the materials that we've tested so

far are clear and when I put them this

far away from the fiber the light

basically just passes straight through

and the fact that the

it doesn't change the direction of the

light it just absorbs it the problem

with this vellum is that it is diffusive

and this will interfere majorly with the

absorption measurement so if we put this

here instead of all the light going

straight into the fiber it comes in at

different angles and would change the

reading so this one is definitely not

going to be the intensity is not going

to be correct but note there's something

very interesting going on we're actually

getting more more light passing from

less than 300 nanometers than we are

from any of the other materials that we

tested it so far it has the smoothest

transmission even though it's lower

across all the wavelengths and finally

let's test a piece of fused quartz so it

looks like glass but it is in fact fused

quartz let's put this in here and it is

amazingly good it's actually very close

to a hundred percent all the way down to

250 nanometers this is why we used fused

quartz to move ultraviolet light okay

let's try something here now I'm going

to take this window of fused quartz and

spray some of this SPF 100 sunscreen on

it and this is hardly scientific of

course but I just sprayed some on there

and kind of rubbed it around a bit now

there's one component of the sunscreen

is quickly evaporating and the rest of

it will stay on the surface of this is a

film

so interestingly it's a

consistent 5 or 6% transmission at least

at the film thickness that I put on

there for for the whole UV range pretty

much and above 400 it's still cutting

out some of the light I mean it's

passing about 80% so let me try taking

it out and just sort of re rubbing

across here just to kind of get another

sample just to see if this really

changes much and you kind of get a sense

of how much is on here I mean it's not a

huge amount it's probably fairly similar

to what would be on skin ok so that's

interesting so we're getting about 2%

transmission now in this region of you

know 300 and something nanometers 2%

let's say okay let me clean this off and

we'll try it with the other sunscreen

and this time I'm going to use 50 SPF

and this one is not a spray so it's

going to be even tougher to to get kind

of a reasonable sort of film that you

know it's not really a scientific test

it's pretty much dumb luck but we're

getting about twice as much UV between

300 and 350 as we did with the previous

sunscreen and this happens to be SPF 50

which is half as high as SPF 100

although as you've probably heard these

SPF numbers are not really the most you

know scientific things themselves kind

of more marketing so the question is is

5% enough is 10% enough how do I know if

I'm going to get a sunburn or not and so

I started researching this and found out

that you know it's been researched quite

extensively and they've come up with

this thing called the erythema action

spectrum or the CIE action spectrum and

what this shows is how sensitive your

body is to getting a sunburn to a

specific wavelength of light and note

that the Y axis is actually logarithmic

so this means that anything any

wavelength longer than about 330

nanometers has almost no chance of

getting you a sunburn I mean it's true

that if you had enough exposure at these

wavelengths you might get sunburned

but it's a thousand times less potent

than wavelengths shorter than about

three

so there's it's very important to know

exactly how much the ultraviolet or what

wavelength of ultraviolet light is going

through the material that you want to

protect your skin or your eyes and as we

saw most materials are quite good at

keeping stuff shorter than 310 nanometer

out of view the even window glass does

it so if the short answer is it's very

difficult to get sunburn through window

glass because it does such a good job of

stopping all the wavelengths shorter

than you know 330 for sure you've

probably heard these terms UVA UVB and

UVC pretty arbitrary definition but it

does actually make sense when thinking

about skin exposure to the Sun where UVA

has almost almost no chance of giving

you a sunburn this includes things like

black lights fluorescent lamps that are

meant for day glow posters that sort of

thing the UVB is actually the thing that

you have to worry about the last thing I

wanted to mention was this concept of

optical density so a lot of times you'll

see od7 with the stated wavelength range

so on these professional actual optical

safety glasses it's important to know

precisely how much light they stop so

the optical density scale is just a

logarithmic way of describing how much

light goes through and the reason you

would want this is that if you're

stopping 99.99% of light and then you

come up with a better material or you

double the thickness or something and

now you're stopping 99.9999% of light it

gets to be kind of silly to say how many

nines

you know 0.9% you've got there so

optical density is just a logarithmic

scale just like we use DV in RF and

power electronics it just makes more

sense when you're talking about all

these orders of magnitude so optical

density is negative log base ten of the

percent transmittance over a hundred so

if you're transmitting one percent one

over a hundred it's going to be a log of

that as to so or negative two and you

take the negative of that so optical

density 2 so optical density seven is

seven orders of magnitude of

of resistance let's see if we can make

an obstacle density measurement for

these unknown safety glasses so we're

back up to the standard setup here are

pretty close to a hundred percent

transmittance and we'll put the safety

glasses carefully in without moving

anything hopefully okay now if we try to

measure this directly let's say we want

to know at 300 nanometers the reading is

super low it's like you know point zero

five percent and that's getting close to

the noise at zero so what I'll do is

increase the exposure time by 10x and

we'll see what this does to the reading

it looks like it's stabilized at 0.6 two

percent and then just to play around a

bit here let me change the number of

averages to one and then increase the

exposure time to three full seconds okay

so I was kind of hoping this is going to

be linear so that 30 milliseconds we are

getting an unreadable thing at 300

milliseconds we were getting like 0.6%

and at three thousand milliseconds I was

expecting or hoping this was going to be

close to six percent but it's actually

more like 2.25 so this sort of implies

that the true transmittance is between

0.06 and point zero two so let's just

say it's point zero four okay so 0.04

percent divided by a hundred minus log

base ten of that comes out to be about

three point four which is kind of

reasonable for safety glasses like this

these were fairly high-end and it was

marked OD seven at those wavelengths OD

four is kind of on the low side for

safety glasses but for these $5.00 or

whatever off Amazon ones this three

point four number is actually pretty

reasonable okay see you next time bye top websites to earn money, online typing jobs for students to earn money, earn skrill money online, earn skrill money, best way to earn money from home, make instant money online absolutely free, trusted online money making sites, online income site, best online earning, money online, earn money from home, earn dollars online, earn money online, earn money online 2019, earn money online by typing pages, earn money online daily, online work at home and earn money, online earning, earn money online free, online money earning sites, earn real money online, e commerce ideas to make money, easiest way to earn money online,