UV Blocking Glass vs. Regular Glass vs. Plexiglas ???

[KrackerG]

During my mission in finding the correct glass needed for my 20” CSL 70w MH, I obtained a reasonable amount of knowledge about glass and UV rays… and even some basics about how light works. However, I’m most definitely NOT an expert in ultraviolet, lights, rays, electrical, or glass or anything that falls in between. But some of the info below may be of use to you…

 

UV LIGHT

 

Ultraviolet light, or UV is present in EVERY single light source…the sun, a lamp, a window or skylights, fluorescent tubes, and halogen bulbs as well. UV rays are more commonly known for wrinkles and sunburn on your skin but also can do some serious damage to it’s surroundings causing fading, yellowing and aging. It’s inherent to every light source…however all manufactures coat their bulbs to protect from these rays…except MH HQI bulbs….Ok??!

 

UV GLASS

 

Now for UV blocking glass, there are a few various types but all of which, filters out over 97% of damaging UV light rays. Your mid-grade UV filter glass has a spectrum cutoff slope set gradual so it allows for a small amount of UV transmission in the 300nm to 400nm spectrum region. From there, all that gets blocked is light transmission below the 300-400nm which is basically blocking the whole UV region and allowing the transmission of the visible light spectrum beyond the 400nm and into near infrared.

 

The more expensive UV glasses differs in overall clarity but has an almost vertical ascent around 400nm, going from almost zero just before 400nm to 90 percent just beyond 400nm. It can also be done tempered for strength and made of pyrex-based material so it can deal with a reasonable amount of heat….

[KrackerG]

Lowe's Glass

 

Regular clear glass often referred to as single-strength glass is what Lowe’s and Home Depot and common glass shops’ stock. It does offer up to 45% ultraviolet light blocking protection but regular glass also has a 10% surface reflection which is noticeable under higher light conditions. There are some regular, non-glare glass that have their reflective properties stripped by chemicals but are often seen as cloudy, hazy, and are not visually as transparent as regular glass.

 

Plexiglas

One of your common clear Acrylic plastics, or Plexiglas, has the same clear appearance as regular glass but having a lighter weight advantage. ** They DO make Plexiglas with 97% UV blocking properties just like glass...BUT they ALSO make a 97% clear plastic tint, similar to automotive window tint( sold for $25 at Lowe’s) Some disadvantages of Plexiglas are the static electricity inherent to plastics…which in turn draws dust. Plexiglas is also suspect to scratching and surface damage. Other common issues with Plexiglas are seen as slight waviness when poor quality acrylic is used causing distortion in light.

 

The only advantages is it’s lightweight; being only about as half the weight of a similar sized regular glass, and the fact that acrylic is virtually shatterproof.

[jasontatro]

Great info Kracker. You definitely did your homework.

 

So.... all that said, which glass are you going to end up using?

[KrackerG]

FINEST GLASS

 

Perfect Vue is new glass product that utilizes a proprietary technology to combine glare reduction and conservation-quality UV-blocking protection. Transparency and mirroring reduction are better than Nonglare but not quite as good as AR Glass (see below).

 

AR Glass is a specialty "anti-reflective" glass made for almost disappearing glass, creating maximum transparency with greatly reduced mirroring and no hazing whatsoever. AR is a higher cost glass option, but this product is definitely worth it in cases where the primary consideration is the elimination of the glass "barrier" and maximum color and detail presence. UV blocking protection is significantly better than Regular glass, but not as high as provided by the regular UV blocking glasses.

 

Museum type glass is the highest quality glass available. This product combines 97% UV blocking protection with AR Glass-quality transparency and reflection control. Suitable for use in circumstances where the ultimate in conservation protection and optical clarity is required. Museum Glass is top-of-the-line glass which can be bought from Stanway Gallery.

[KrackerG]

My 20”and 30” CSL UV blocking glass prices were:

 

6 ½” x 20” was $17

6 ½” x 30 was $30 (ouchy Reefer_Buddha!)

 

It is good for protecting 97% of UV-A and UV-B harmful rays which is the highest w/o distortion. 8% light reflection. Light reflection is how much light is "bounced back" from the surface of the glass. UV blocking is how much light in the 300-380 nm range is prevented.

 

This thread is in conjunction with "My "CUSTOM" SeaLife 20" MH retro conversion thread. However, I felt this data could be useful to anyone using ANY non-UV shielded double ended HQI bulb. This data was taken from after speaking with professionals in the glass industry along with information from glass manufacturer’s information data sheets. Please feel free to post your comments.

[bgoode]

How does thickness affect the blocking abilities? I assume the thicker the glass, the more UV is blocked, but is that correct? What is the minimum thickness to be effective?

[jasontatro]

I wouldnt imagine that it would have to be all that thick as the UV blocking is probably just a thin layer within the glass or a coating on the glass.

[KrackerG]

ooOOOOO....good point! dealing with 2.5mm thickness (1/8")

 

i'm sure the values go up in thickness but 1/8 is all that's required. you may be loosing some USEFUL spectrum rays when using thicker glass...gotta call the glass guy tomorrow:P

[csxno1]

Ok kracker this info. is all well and good, and i can see this being useful for keeping your carpets from fading, but isn't the purpose of USING the metal halide bulb is the increased UV output so that you in turn get the vibrant colors associated with the UV protectent colorations in sps and the like?? i would think if you filtered all or most of this out with some exspensive glass your defeating the purpose of putting a metal halide on the tank, especially with only a 70 watt, we're not talking 400 watters here. Just a thought as i am making the same mod to my 20" CSL light as you did, but i think regular tempered glass shuld be fine. Just my 2 cents.

[KrackerG]

bgoode-- the thicker glass...say 1/4" is still 97% UV protection. But the light that is reflected is probably around 20%...not good. Light transmission is lower too because it has to penetrate through thicker glass...not good again.

 

csxno10-- true. simulating the natural sun's rays is really what lighting a tank is all about...right??! the advantage of using metal halide is the increase in visable light output in the USABLE spectrum range (300nm(blue) and up) the lower spectrum lighting (below 300nm) will do nothing good for your tank...or carpet at that! as for the 70w vs. 400w...it's not the watts your dealing with...either will still throw off harmful UV rays.

[digz]

but will putting the uv glass up cause me to lose my tan?

[Acrylics]

One of your common clear Acrylic plastics, or Plexiglas, has the same clear appearance as regular glass but having a lighter weight advantage. A BIG misconception about Plexiglas is about it’s UV filtering properties. It is the same as provided by regular glass!!

Not at all true. Generally speaking, acrylic transmits absolutely no UV below 320nm and doesn't really transmit any until 360nm then it's a linear slope to 400nm, exactly the same as UV filtering glass. The average UV absorption or "blocking" by acrylic is right around 93%. This is not a misconception at all, feel free to check the physical and optical characteristics from any acrylic spec sheet. Whomever told you this is just plain wrong.

 

BTW,

http://www.atofinachemicals.com/atoglas/te...rch/PLA17c3.cfm

Atofina is the mfr of "Plexiglas"

 

http://www.cyro.com/Internet/SiteContent.n...256ADF0049AEC9/$File/1213F+UV+trans+TB.pdf?OpenElement

Cyro Industries is the mfr of "Acrylite"

 

Polycast and Lucite have similar numbers as well.

 

James

[KrackerG]

thanks James for the clarification. Anyways, I have sinced spoke w/ my glass guy to find out some truth....and he stands behind what he told me 100%. He said they also DO make UV blocking plexiglas but not all plexiglas is the same. He is willing to bet his 25 year old business on it. He showed me the spec sheets you were referring..all the info i posted was told to me by my LGS or was taken from glass manufaturer's spec sheets. He showed me the spec sheets you were referring to and directed me to this website for more info.

 

EDIT: See this website for more info:

Plexiglas/non-glare plexiglas has NO UV-blocking protection properties beyond that provided by Regular Glass.

[Acrylics]

all the info posted was told to me by my LGS or was taken from glass manufaturer's spec sheets.

First off: Nice to meet ya

Secondly, you are going only to his shop, listening to what a "glass guy" is saying, IMHO, he is a glass guy - why would he say anything good about acrylic? Same goes with glass mfrs.

Also, regular or "float glass" (which, BTW, is just a mfg process) can have UV transmission rates of below 1% to ~80% depending on which manufacturer he goes to, the amount of iron and other impurities, and a coupla other factors. To base his numbers on one mfr is manipulating the truth IMHO, if he said this was an average, I could agree, but to come out and say "regular glass" and come up with a number is bad form IMO. Do a Google search on float glass and UV filtering and/or transmission and you'll see what I'm referring to.

BTW, his statements regarding static and acrylic are only a half-truth, a quick wipe with Brillianize will completely eliminate this "issue".

 

Anyways, I have sinced spoke w/ my glass guy to find out some truth....and he stands behind what he told me 100%.

While I understand you have no reason to believe me over him, he is quite mistaken.

 

He said they also DO make UV blocking plexiglas but not all plexiglas is the same

This is quite true, they make acrylic specifically to transmit UV (called UVT, for tanning beds). They make it to block out 100% of UV, amber in color, used in scientific applications. But normal run o' the mill acrylic such as Acrylite, Polycast, Lucite, and Plexiglas transmit very little UV overall, none @320nm, doesn't really start to transmit 'til 360nm, and exactly the same slope as UV cutoff glass.

 

He is willing to bet his 25 year old business on it

on what? that not acrylic is the same, hehe, funny

If he wants to bet on anything regarding his statements about UV and acrylic, I'd gladly take him up on it.

 

He showed me the spec sheets you were referring to and directed me to this website for more info:

What was he using to back up his claims? a website written by him? come on, do better than that. I've given you mfrs specs (from more than one mfr) on the acrylic, and it was either Rob Toonen or Sanjay that did some testing on this a li'l while back if you'd like that as well. Of course they'd rather sell the UV "blocking" acrylic at 3x the cost though.

While I commend the effort you've put forth, I think you've "put all your eggs in one basket" in taking what this guy says as gospel. Did he bother to mention anything about acrylic made specifically for HID UV shielding?

All that said, I am not an acrylic fan for shielding HQI bulbs, I still use glass for mine simply for the heat issues.

 

Anyway, nice to meet ya

 

James

[KrackerG]

so would you agree to the fact that the Lucite clear plexiglas (or even the regular glass) sold at Lowe's is NOT UV blocking glass appropriate enough for use under an unshielded metal halide bulb??

So you are use what type of glass...? is my glass ok?

 

EDIT: Michael's Arts and Crafts website--> Michael's Store Locator

[Acrylics]

so would you agree to the fact that the Lucite clear plexiglas (or even the regular glass) sold at Lowe's is NOT UV blocking glass appropriate enough for use under an unshielded metal halide bulb??

Nope

I'll start with the acrylic side of it. *Generally speaking*, acrylic has the same UV blocking ability of UV cut-off glass. While it's not marketed as UV blocking for the simple fact that the acrylic mfrs sell a "UV Absorbing Acrylic" at 3x the cost and only 5% more UV absorption. The major problem with acrylic in this application is the heat issue.

While "glass" may not be perfect by any means, it will filter out much of it - how much? well, depends - as you know. IMO you don't want to filter out *all* UV. A certain amount will be filtered out by the glass, some will be attentuated by the water, some will be reflected by pigment in the corals, and the corals need *some* UV for synthesis of certain vitamins necessary for calcium uptake. To block it *all* out would be a mistake IMHO.

So, while not "UV Blocking" materials, I think both are very adequate for this purpose. BTW, there is still debate as to whether or not shielding is necessary at all, between such folks as Eric Borneman, Dana Riddle, and others.

 

like i said in beginning of this thread, "I’m most definitely NOT an expert in ultraviolet, lights, rays, electrical, or glass or anything that falls in between."

I don't claim to be an "expert" on UV nor it's detrimental effects on corals. But, I have been in the business of building exhibits for museums and public aquariums where I've had to learn a working knowledge. In so doing, I"ve had to research and work with glass and it's optical coatings as well, but to be honest I claim no expertise in glass, but I do know that one cannot say "regular glass filters out x amount" without qualifying that statement.

My expertise is solely in acrylic, it's properties, manufacturing, and applications, just so ya know

 

So you are use what type of glass...? is my glass ok?

Simple run 'o the mill 3mm float glass that Pat at PFO gave me with my pendants, each BTW house 250w 10,000k HQI, 150w 20,000k HQI, and 2 x 75w VHO actinic. I've had them on my tanks for years and no bleaching or other light related issues. The only reason I keep glass on there at all is that I keep the bulbs about 6" above water line and the glass acts as a barrier between splashing water and the bulbs, which would explode should the be splashed with water at working temps.

 

IMO, the reason that no the guy at Lowes or the glass shop will tell you it will be fine is two-fold. A) he doesn't know how much *actual* UV absorption and at what wavelength that UV absorption will be on each and every piece he sells - this would be totally impractical and if he did tell you it would be fine, he opens himself up to a liability in conditions he cannot control. Besides, they would rather sell the more expensive "UV Blocking material" at 3x the cost. just business

 

James

[KrackerG]

hmmmm, interesting. thanks james, all well said and understood...and it all makes sense. so a $6 piece of glass is all thats need...cool. BUT, you also say that using an acrylic plexiglas shield under a HQI metal halide is a major problem because of heat...?? how hot can acrylic stand before meltdown?? is there such a thing as tempered plexiglas??

[trmiv]

Sorry to drag this thread out of the depths, but I just want to be sure I am clear on what I have read. When I need to get my shield cut for my new 70w MH modded CSL hood, I can just take the acrylic piece I have now to Lowe's and have regular glass cut to that size and use it?

[trmiv]

I went to Home Depot and got some glass cut, but I still am not sure about this. Is this glass going to be good enough?

 

Now I'm hearing from various threads that this regular glass is going to crack from the heat of the MH bulb. Urgh. What is the answer here? Do I need to plunk down the money for tempered or Borosilicate glass?

[Acrylics]

Regular "float" or "window" glass is fine IME. Just so ya know, PFO Lighting has always used just plain ol' float glass. In each of my pendants I keep 2 HQI bulbs and 2 VHO and never an issue in this regard. While the cracking thing *can* happen, it's actually quite rare and not some I'd worry about.

 

HTH,

James

[trmiv]

I went ahead and just got some tempered glass. Better safe than sorry, and I don't trust myself around glass.

[BallR]

i listened acrylic and i went ahead...6 bucks for each glass...good thing cus i broke the first one..cant imagine myself breaking the $35 uv glass w/o givin myself a thorough a$$ kickin....

 

 

ShHHHWEEeeeet info got more dead presidents to spend on the LRB)

[szesteve]

Hmmm...

 

This is really useful, I'm also getting the 70W MH from LampDr.

 

So just normal glass from a glass shop is fine??? Or do I need tempered glass?

[trmiv]

regular will work fine. i had a regular piece, and it was fine, but i switched to tempered because i didn't trust myself with the glass. tempered is harder to break. if you want to be a bit safer you can get tempered. that will make it stronger, and a little harder to break, especially if it gets hot water splashes on it.

[wallywaltt]

I just bought the home depot Lexan XL acrylic. I think a few other reefers are using it as well. It says its 300 times stronger than glass, won't yellow for at least 10 years or so, can withstand high temps, and is uv protectant. I bought a piece for $8.88 and they cut it to the dimension I wanted for free. Just read this thread, so I'll let you know how the Lexan XL holds up when my tanks up.