Excuse me, Mr. Don. [img]/ubbthreads/images/graemlins/wink2.gif[/img] Sorry for be'in an [img]/ubbthreads/images/graemlins/duh2.gif[/img] ignoranimous here, but, could ya tell me, What the heck is SODA LIME Glass?
Is that what I drank out of? [img]/ubbthreads/images/graemlins/icon3.gif[/img]
I am not up to speed on all of the various glass materials but soda lime is a very common one and recommended to me for these windows. It purportedly has good physical charactoristics for its application with LED lights. A google on soda lime will likely bring you more than you want to know! If I were looking for windows that had a higher thermal range or lower CTE, there would be likely better choices of material. [img]/ubbthreads/images/graemlins/icon3.gif[/img]
Perhaps some experts or more knowledgable members can chime in here. I believe Newbie had a post not so long ago discussing various window materials?
Soda Lime or regular float glass, are all normal green house windows.
Optiwhite, crown glass, borofloat, pyrex, and borosilicate are all clear. It is also known as waterwhite glass.
Getting it clear is only half the battle, typically clear will get you to 91.6% of the light passing through, the next step is to go for doublesided AR (anti-reflecitive) coating. Depending on thicknesses, AR coated window glass (which is green), passes more light than the clear glasses without AR coating.
Okay, so, what type of glass do you have in your hand, turn it on edge, and look from the edge to inside the glass. If it is green, you have soda lime float glass. (otherwise known as window glass).
Soda lime float glass (a.k.a. window glass) that is often used in flashlights causes a shift in emitted light towards the green portion of the spectrum. So you could have the whitest white emitter shift out of the perfect white bin into another bin when using it, depending on where it sits in the bin. How far it shifts will depend on the glass thickness.
I should run a test one of these days to see exactly how far the soda lime float glass actually shifts the light color, on top of dropping the light output level.
Without AR coating, you have a 3-5% drop in light output (typically 4%) for each face, for a total of 6-8% loss, on top of 30 - 15% typical losses for common flashlight reflectors. You can drop the reflector loss to a total reflector loss of 2 - 15% when you go to lab or telescope quality reflector coatings.
You can make an aluminum reflector from 100% pure aluminum (the normal aluminum you get is not pure but an alloy), and get the reflectance up to 93%, by putting a perfect polished surface on it. Unfortunately, on contact with normal air, it rapidly degrades from this immediately.
This is why they do it in an inert atomsphere, and do a special protective oxide overcoat. Most of the oxide overcoats will degrade the reflectivity. Some special oxide overcoats will actually improve the reflectivity.
Though you can get a rather specialized hi phosphorous Nickel that is rumored up to 80% reflective if it is done properly.
Also if looking this stuff up, note that solar reflectance, and normal reflectivity are two different numbers, and even the folks that use the terms get them mixed up. Solar reflectance includes IR and UV reflectance, though some only use visible + IR to make the numbers look better. In the end, it is always best to ask for a graph of reflectivity vs. wavelength.
Add all this up, and thats where flashlight manufacturer's claims that use the light source lumens for the flashlight lumens are easily 30-50% too high. Very few actually measure it.
Just to add in some related info given by Don on the anti-reflective coating on the glass from another thread -
[ QUOTE ] McGizmo said:
It is apparently pretty hard and likely will scratch with the proper abrassive but is not too sensitive as to need pampering. When one considers the coatings on good eyeglasses as well as binoculars and other devices which have exposed windows or lenses, it would seem that any potential downside to partial removal or scratches is overwhelmed by the upside of the improved light transmission of the optic element being coated. [img]/ubbthreads/images/graemlins/icon3.gif[/img] wait..... google search on Luxar......................
" Luxar® glass is the new leader in anti-reflection glass. Unlike many similar anti-reflective products which are soft coat, Luxar is a hard coat which allows for easier handling, longer shelf life and makes Luxar an excellent candidate for exterior applications that are subject to environmental stress and constant cleaning. Luxar's anti-reflective coating reduces the glare of uncoated glass from 8% to 0.5% when coated on both surfaces."
From the supplier of these specific windows, I have borrowed the following transmission graph:
I suppose this information should be place elsewhere in another thread. [img]/ubbthreads/images/graemlins/blush.gif[/img]
Thanks for the post. The windows I am using are from soda lime clear with Luxar coating both sides. These windows are clear on edge and do not have any green tint what so ever?!?! Further, if the graph above can be believed (refer to the ClearView with A/R 2 sides which I am using) I would assume that if there were any tinting or filtering of the spectrum that this would be seen as a spike or peak in the transmission curve?!?!? [img]/ubbthreads/images/graemlins/icon3.gif[/img] Perhaps a comparison above of normal window glass where you can see the curve drop at about 575 nm can be interpreted to be the loss of the reds and hence the apparent green? It looks like the windows I am using don't drop until 650 nm. Since the visible spectrum is 400 to 700 nm, it would seem that these windows do a reasonable job of light transmission. [img]/ubbthreads/images/graemlins/icon3.gif[/img] In comparing the Clear View with and without A/R coating, you can see that the A/R is less effective at the UV end in terms of aditional transmision over non A/R and there is also a drop at the red end.
Well at any rate, I deferred to the "experts" in the choice of material for these windows. Heck, I was happy with mineral glass windows but wanted to improve the light transmission with the Aleph lights even though the windows have cost from 4 to 8 times more than mineral glass. [img]/ubbthreads/images/graemlins/thinking.gif[/img]
"though the windows have cost from 4 to 8 times more than mineral glass."
Yeah, nothing is free. Sure is nice to gain an extra 6-8% light though.
I'm looking at the chart and see dramatic roll off in the blue and red ends...guess what tint that makes it?
Doesn't have to be peaks, for filters, you'll see a drop. Your perhaps comment is correct.
Go to a window glass shop, and take a look at the glass edge on, even short pieces are green. Shoot, even hit up your local home depot and take a look.
I use AR glass on a routine basis...
As of June 30, 2004, JDS Uniphase had approximately 6,000 employees.
The OCLI subsidiary currently employs approximately 1,600 people worldwide
"Throughout its 52-year history, JDS Uniphase (aka OCLI's mother company) has provided its customers with high-quality optical products utilizing multi-layer interference coatings. Our first products were anti-reflective filters for high-altitude aircraft cockpit instruments. Since the Company's inception shortly after World War II, we have developed sophisticated process techniques for manufacturing optical thin film coatings that enhance or modify the behavior of light. "
"Optical Coating Laboratory, Inc. (OCLI) is the world&#8217;s leading manufacturer of high efficiency anti-reflection coatings for Display Applications. Leveraging over 50 years of thin film coating expertise... You won&#8217;t find a better anti-reflection display enhancement product than OCLI HEA® anywhere in the world."
Bleh, lexan windows (polycarbonate), numberous reasons why I don't like those. Personally if I have to go with plastic, I personally prefer 2 sided AR coated acrylic instead, with an abrasion resistant hard coat, if needed.
If you look at the graph above, do you see a dramatic roll off on clear view? That is the glass. Now with the A/R coating, there is this dramatic roll off of maybe what 8% between 400 and 450 nm and then what 2% between 660 and 700? [img]/ubbthreads/images/graemlins/icon3.gif[/img]
So maybe I could avoid the drama by not getting the A/R coating!!! [img]/ubbthreads/images/graemlins/tongue.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img] I do see a drop in the normal window glass starting at 550 nm and I have actually cut a fair amount of glass and mirror in the last 30 years and I do know what you are talking about when you mention the green glass on the edge. These windows are not green. They are clearon the edge. I think you are lumping all soda lime into a group and I suggest that there are some differences! As evidenced above in the ClearView VS normal window glass. Now do you suppose that the same A/R coating on a different substrate will have markedly different transmission charactoristics or do you think that some of the drop off as shown above is inherent in the coating itself?
Last comment. If one were to take the Luxeon relative spectral power distribution and adjust it by the percentages of transmission through these windows, would the overall effect be that noticible? We would knock 1% off the top of the "spike" centered around 440 nm and maybe 1 or 2% off the meager output that is up in the high 600's??
I have no concern about these windows throwing a tint on the LED's output. The gain of transmission from the A/R coatings is likely not noticible to the eye but no doubt measurable with the aid of a light meter. I believe these windows are an improvement over mineral glass and lexan as materials and I feel they make a viable component for the Aleph lights. [img]/ubbthreads/images/graemlins/icon3.gif[/img] Some experts advised me to go with this material and so I did. [img]/ubbthreads/images/graemlins/blush.gif[/img]
Right, Clearview is a very specialized soda lime glass (unique)(another variant is called optiwhite), that has reduced iron which is what gives the glass the characteristic green tint. The drop in the red and blue of clearview or optiwhite glass wouldn't be seen in the beam.
I know it is a combination of both. You can see it in the non AR coated clearview. I also know with even clearer glasses, the AR does cause a slight drop is red and blue.
Clearview is not as tough as the borofloat/borosilicate group of glass, and one of the leading materials that folks are familiar with from this group is Pyrex. It's toughness is the main reason it is used for labware. It's not as brittle, and it is more chemical resistant than soda lime glass. This type of glass is also utilized for more critical applications, such as LCD displays.
Looking at OCLI's chart for HEA or HEA-2 (BBAR), you can see some drop in the red and blue in the AR coating itself. This is why you see a slight purplish hue in a direct reflection, this is the MgF2 based coating. A less common type is SIO, which has a green hue in a direct reflection. The quality of the MgF2 coatings, and how well they are applied, when not done correctly, will show more of a red or more of a blue cast.
AR coatings can be applied by vapor vaccuum deposit, sputtering, and dipping. There is a big difference in the durability of the coatings, dipping being the worst of the bunch.
Geesh, normal standard soda lime float window glass is green. This will alter the color of the beam.
One version of the higher end Borosilicate glasses for LCDs is made by Corning and is called Eagle 2000. Note the flat optical transmission curve.
The manufacture of float glass is a modern technique that has increasingly replaced sheet and plate glass production since the 1960's. It produces glass that is nearly as high in quality as plate glass but does so in a single operation which, like sheet glass, requires no further processing. The technique was pioneered by Pilkington Brothers Ltd. - molten glass is fed into a float bath of molten tin. The glass floats on the molten tin as a ribbon and cools gradually as it travels across the surface.
Well thanks! Hopefully JDriller has his answers! [img]/ubbthreads/images/graemlins/icon15.gif[/img] I suspect that many of the mechanical as well as chemical resistances of the various window materials have little to no bearing in their application as windows for LED flashlights. The good news is that the windows are replaceable and should they either break or melt in acid, one can always install a new one. [img]/ubbthreads/images/graemlins/grin.gif[/img] I personally am looking into sapphire crystal with A/R coating for my own lights. I am sure these will be real cost effective! [img]/ubbthreads/images/graemlins/icon15.gif[/img]
Hardcoat and/or Abrasive Resistant Anti-Reflective coating, how hard is it? my UCL coating has held up pretty well against sand and a massively punitive environment at work, but it is a bit scratched, is this hardcoated? Is the luxar hardcoat even harder? How hard?
PS mcGizmo, if you get sapphire with AR coating the scratch resistance won't be better than regular glass with the same AR coating would it?
I really don't know how the hardness of the A/R coating compares to the substrate. I got a couple samples of A/R coated sapphire but they are only coated on one side. Obviously, that coating would go on the inside. I have a silly fantasy of a limited run of a Ti light where cost is no object but construct and the use of the best materials possible is. Cost effective things like a gold plated sterling silver heatsink and gold plated reflector. [img]/ubbthreads/images/graemlins/icon15.gif[/img]
It would be a small light and the LED efficiently underdriven.
A comparison plot of 2 sided AR vs. Mineral Glass:
This was further borne out, when the lens of a HDS LED flashlight was replaced with mineral glass, during Gransee's calibrated integrating sphere tests. It was found that the mineral glass alone caused an additional 13% of loss.