Led Panel Tech:" Cabriolet " or no ?

[stardustsailor]

To cover or no ?

I mean ....

Should the leds be covered with some kind of thin polymer screen -mainly for protection - or no ?
Hmmm ....

That is a tough one ....

And somewhat ,of rather great importance ....

Seems like a "detrimental" detail ,eh ?

Nah...

 

[stardustsailor]

To cover ?

Ok ...

Let's cover the precious little ones ...

Simplest way ,to protect them ...
...
Protect them from(possible) physical impact/abrasion and from(possible) chemical corrosion /deterioration ,
which might affect seriously their normal operation and service life ....

Yeah....
But there'a "price" to pay ......

- Light Output is affected ...
-Cooling,somewhat ,is also affected ....

Some basics :

 

[jubiare]

It'd be nice one could just wipe on them from time to time eh eh eh

 

[stardustsailor]

Refraction ....

....

At a case of covered leds ......

Light exiting the led's lens into air ...Pass through polymer (plastic ) screen ...
To exit again into air ......

Air=>Polymer=>Air .....

From led light falls to screen ,having different angles ....
Starting from 0° ( perpendicular incidence ) up to a certain angle (depending on led's lens/case ) ....


Passing through the screen light ,refracts towards the incident angle ..
It "zooms inside" ,in a way ...

Exiting into air again ,it refracts away .....

ni*sinθi = nt*sinθt ....
nt*sinθt = ni*sinθο...
ni*sinθο=ni*sinθi

So ,in other words -theoretically - a protective screen does not alter the emission angle of led(s) ,
but rather " narrows " the output light cone(s) ...
....


So ,a screen decreases somewhat the " footprint "...
Without affecting emission angle of led(s) ....

 

[stardustsailor]

It'd be nice one could just wipe on them from time to time eh eh eh

We'll get to that point ....
Almost all led manufacturers ,suggest never to be done ...

 

[stardustsailor]

From refraction ..Another "phenomenon" occurs ,
inside the polymer matrix of screen
TIR ..
Total Internal Reflection(s)...
..


Oh ...That is a serious one ....

While utilised in led lens manufacturing ....

In case of a screen ,covering the leds ...
Things aren't that ..."nice " .....

Example ...
Two leds .....
Let's say one Oslon SSL 80 (full cone angle=80°-at where rel.power is at 50%- ,half =40° )
And one Oslon SSL 150° ....

Let's take the case of an Acrylic ( PolyMethyl-MethAcrylate aka PMMA aka Plexiglass... ) transparent screen ...

With the Oslon SSL 80 ,light with incident(to screen ) angles over 42° ,get reflected back ...
But this led has it's 50% of rel. output light power at 40° half angle ..
Light that gets reflected back ,has rel . power of less than 50% ......

But for the Oslon 150...
Things are different ...Since it has it's Half Angle at ~75° ....
So ..Plenty of light,is actually reflected back ,from screen ,not exiting the other side ....
And ,in fact ,is quite a big amount of light loss .....

So ....
Material of screen and led's emission angle ,are tightly related ......
http://refractiveindex.info/?group=PLASTICS&material=PC
https://en.wikipedia.org/wiki/High-refractive-index_polymer

 

[stardustsailor]

Power losses ...
Absorption and Fresnel losses ....

Solid materials,no matter if of great transparency ,will still absorb an amount of light ,"passing through "......
Depending on material used ,it's purity ,colour,etc ,those losses range from detrimental to really high .....

Polymers " age "...
Specially under constant short wavelength radiation ( U/v-Violet-Blue light ) ...
Heat* ,makes things worse ....
That aging (cracking-chipping-yellowing-etc ),seriously impacts light output power ,exiting the screen ....


.......

Again ,Fresnel losses for a wide angle led ( >120°),are quite high ,if an i.e. acrylic protective screen is used .....

Summed up :
-TIR Loss
-Material Absorption Loss
-Fresnel Loss ....

....The wider emission angle leds used ,the worse ....

 

[stardustsailor]

Heat issues ....

Well ...

Covering the leds (and of course the metal core pcbs & heatsink surface ,that leds are installed to ..) ,
does impact cooling ...

Well ,to be more precise,at least if that is not "overridden" somehow ....
Swedish led grow panel designers ,are really a bunch of clever guys/girls ,there... !

They chose to cover the leds ,with a high quality screen and manage to "override " the possible heat issues ....

Led fixture case ,is actually covering the mcpcbs/heatsink of leds ...
Leaving only the leds exposed ,through a "grill " construction/design ....
So,actually case ,conducts heat from "ledside" ,which is covered with the polymer screen ....
...
Which heat in other case of exposed leds/mcpcbs/heatsink ,would have been radiated /convected to air ....
Indeed,clever thought & design ....
They have taken into account ,the possible heat issues ,generated by covering the leds with a screen ...

Other designers ( i.e like myself or Mr.Hans ) choose not to cover the leds with a screen ,but do protect them (as much as possible ),
utilising other methods ....

Building a "top seated, grilled ,kinda case -kinda heatsink " to cover the mcpcbs/heatsink and serve as screen " holder " ,yes,it is a really good idea ...

But ...
As also good are other ideas ...
With their own "limitations " & "advantages"- pros 'n' cons - ,of course .....

 

[stardustsailor]

Now ...
Take a brake...
Have to finish the study of incidence of
my new "spectrum " ..

I call it "444" ..

( 4x NW 4000°K LCW CQ7P.CC _ 4x WW 2700°K LCW CQ7P.CC _ 4x Hyper Red LH CP7P ) ..

Take a glimpse ..
[video=youtube;KAJvJ_-htjg]http://www.youtube.com/watch?v=KAJvJ_-htjg&feature=youtu.be[/video]

 

[stardustsailor]

So...
In order to have a good blended light ....
Leds have to be closely "packed " ...

And then covering them with a polymer screen ,is not the best idea....

So...

 

[Chronikool]

I love how they create rays of multiple 'Mt Olympus peak' life bringing light.....

 

[stardustsailor]

I love how they create rays of multiple 'Mt Olympus peak' life bringing light.....

...for you,brother ....
[video=youtube;ShMRW3dFMlI]https://www.youtube.com/watch?v=ShMRW3dFMlI[/video]

 

[650baquet]

I have an HTG 432w 7-band LED panel, i know it's now great but it's cool to experiment with. so far i experience way better yield with my 400w hps but the nugs are naturally more dense and flavorful under the LED. I also have the 240w 7-band and a Kessil H150 magenta great for filler light/supplemental light

 

[stardustsailor]

I have an HTG 432w 7-band LED panel, i know it's now great but it's cool to experiment with. so far i experience way better yield with my 400w hps but the nugs are naturally more dense and flavorful under the LED. I also have the 240w 7-band and a Kessil H150 magenta great for filler light/supplemental light

Yeap...Whatever suits you ,brother ...

 

[stardustsailor]

So ...

Regarding Wide emission angle leds, protective polymer screens ,is not the most efficient way to protect the leds ...
The simplest yes ..Efficient ,not at all ....

So ,it's best for that kind/type of leds to remain uncovered by any sort of flat polymer screen or film ...

Footprint will decrease somewhat , as overall output power will also,in rather 'un-neglectable ' degree ..
Even if, best quality material is used ,for screen .....
,,,
While ....
Narrow emission angle leds ,( <120° ) ,do better under a protective polymer screen ....

But then ,their narrow light cones ,have to be as "close" as possible .....
Towards forming a single cone of light ....
Otherwise ,light " inconsistencies " will/might occur ...
Due to narrow light beams ..("cones" )
And generally ,that is a non-wanted effect ...

So ,they have to be as closely "packed" as possible .....

But then ....Cooling ,becomes even more of an important issue ....
And the polymer screen ,"isolating " the leds from rest of environment ,makes things worse ....


What about if just leave the leds uncovered ?....
Well ...

-Physical Damage ...
&
-Chemical Damage...
......

Those are the two main problems,to deal with,at that case ..

....

 

[stardustsailor]

Well ...
Let us start with the chemical corrosion ...


The uncovered leds ,are going to be used for horticultural purposes ...

So ...
They're going to be exposed to a wide range of ambient Temperature...For example 15°-25° ...Or 25°-35° ...
Also ,they are going to be exposed in rel. humidity conditions ,sometimes close to 100% ....
Dripping Wet ....
As also they might be exposed to droplets/spills of various chemicals which might be oxidising / corrosive ..
(I.e Ph up & down solutions ..) ..
Or to "sticky " organic chemicals ....
Which brings another type of chemical corrosion ..
Bacterial/Fungus corrosion .....
Or "contamination " ,if you'll prefer ...

If led has iron /copper /aluminium contacts ,soft -thermoplastic- polymer parts or other parts made of non corrosion resistant materials ,
then simply ,leds won't last long ,in their " horticultural purposes " assignment ....

Corrosion -Resistant leds ?

Oh ,yes .....

Most of tiny ceramic packages ,are of that exact type .....

-Hard Silicone or Epoxy lens/'encapsulants',used ......
-Ceramic ( AlN / AlO / BN /BeO ) cases,used....
-Gold (plated) metal contacts ,used ....
All of them ....
Alkali-Acid -Oil/Fat-Organic Solvents & Acids -- resistant materials.....

BUT ....

Oh,yes ....

While they resist to all that .....
They won't resist ..dirt ....Dust ,"organics" staining droplets ,etc ...

Eventually ,they will get dirty/dusty ,somehow ....

How about cleaning them ?

....
Not a simple issue at all .....

 

[stardustsailor]

....

Some useful notes ...
...

Personally I use a small ,with a tiny tip of soft natural hair ,painting brush ,dipped in IPA (Isopropyl Alcohol ) ,
If to clean the leds ,from my messy -prototype- done job ....

Purified Compressed Air (spray can ) for un-dusting / keeping clean ...
&
IPA,for the more severe "contamination" cases ....

 

[guod]

http://en.wikipedia.org/wiki/Gorilla_Glass
http://abrisatechnologies.com/specs/Gorilla Glass Spec Sheet.pdf
http://www.corning.com/docs/specialtymaterials/pisheets/PI2317.pdf

 

[guod]

People call it Merkaba but for me...
http://en.wikipedia.org/wiki/Close-packing_of_equal_spheres

 

[stardustsailor]

Still ,dear Guod ...
TIR phenomenon is not avoided and it's impact on wide emission angle leds ,is still rather great ...

Material you list ,does absorb ~10% of light at region 400-750 nm ,at average ....

Add to that ,Fresnel losses ...
..... And Losses from TIR ....


It goes(how far? ) beyond ~10% of total output power ...

...

Critical Angle for Gorilla Glass ....

n air / n gorilla glass ....

~1 / ~1.5 = 0.66666666=Sin &#920; critical .....


&#920; critical of Gorilla glass = ~41°

Still...

Good idea ,though ...
For tv screens ,laptops ,palmtops ,mobiles ....

In use for led grow panels ,it does not differ much than ordinary,"humble" plexiglass ..
It's just way thinner ,for same strength ....

Still ..