U.V. filter

**MIOPE** · 10-22-2010, 03:51 PM

We apply the U.V. filter (the fast one) to every CR-39 processed. We use a U.V meter from BPI that shows the percentage of U.V. not filtered and also has 3 lights. Green (3% or less) yelow and red. It is adjusted fecuently with a test lens. We only pass lenses that shows the green light which means 97% U.U blocking or more. Sometimes the lens gets a little yelow color and some patient do not like it so we redo the job. This yelow color is higher on some lenses and in others is almost invisible. Do not know why.
Recently i heard that the new Ansi Standards permit up to 5% of U.V. Light not blocked.
I went to the page of Ansi Standard on Opticampus but did not see anithing about U.V. filter.
Is it true about this 5% of U.V. permited?

**uncut** · 10-22-2010, 08:57 PM

Originally Posted by MIOPE

We apply the U.V. filter (the fast one) to every CR-39 processed. We use a U.V meter from BPI that shows the percentage of U.V. not filtered and also has 3 lights. Green (3% or less) yelow and red. It is adjusted fecuently with a test lens. We only pass lenses that shows the green light which means 97% U.U blocking or more. Sometimes the lens gets a little yelow color and some patient do not like it so we redo the job. This yelow color is higher on some lenses and in others is almost invisible. Do not know why.
Recently i heard that the new Ansi Standards permit up to 5% of U.V. Light not blocked.
I went to the page of Ansi Standard on Opticampus but did not see anithing about U.V. filter.
Is it true about this 5% of U.V. permited?

Since I am in Canada, I am not able to answer the question about the new standard permitting up to 5%....however I would suggest that you aim for a higher standard, and that would be to make all your lenses as close to 100% as possible.

Remember Vogt's law..."Where there is transmission, there is risk of lesion".

A true UV 400 lens has a slight color to it. This can be disguised by adding a balancing color dip to make it appear more pleasant. I have used a combination of pink/brown, or grey/blue, depending on the frame or complexion color. I would record the ones that are more or least colorful, it may be brand, or index specific; that would enable you to predict which ones are more undesireable.

I am not familiar with the BPI unit..does it read up to 380, 390, or 400?

**MIOPE** · 10-23-2010, 07:32 AM

Just checked here http://www.callbpi.com/htm_cat/meters.htm and they say
"Our photometers accurately assess the upper portion of the UVA band between 350 and 400nm"
The one we use is BPI Computer Call III.

I has notice also that some CR-39 lenses gets a more intense yelow color than others once the UV filter is applied. Even we have had a few cases where the patient returns a few week later with one or both lenses with a higher yellow color that when we dispense the lenses. This is not frequent but i would like to know why.

**MIOPE** · 10-23-2010, 07:40 AM

Just checked here http://www.callbpi.com/htm_cat/meters.htm and they say
"Our photometers accurately assess the upper portion of the UVA band between 350 and 400nm"

They also say
"For customers who require photometers that read to the ANSI standard, BPI® also sells units that read lenses to 380nm and gives a percentage transmission reading based on 315nm to 380nm."

The one we use is BPI Computer Call III.

So which is the correct portion of UV to be blocked to produce a safer lens?.

I has notice also that some lenses gets a more intense yelow color than others once the UV filter is applied. Even we have had a few cases where the patient returns a few week later with one or both lenses with a higher yellow color that when we dispense the lenses. This is not frequent but i would like to know why.

**Chris Ryser** · 10-23-2010, 06:47 PM

Originally Posted by uncut

I am not familiar with the BPI unit..does it read up to 380, 390, or 400?

A few years back when I was still selling US made Uv meters we had the choice between selling the ones that would show 100% absorbtion at 382nm or at 400 nm.

Actually I was told that the 382nm units would make for about 75% of the total sales.

also see: http://optochemicals.com/prism_article.htm

**uncut** · 10-23-2010, 08:59 PM

Originally Posted by MIOPE

Just checked here http://www.callbpi.com/htm_cat/meters.htm and they say
"Our photometers accurately assess the upper portion of the UVA band between 350 and 400nm"

They also say
"For customers who require photometers that read to the ANSI standard, BPI® also sells units that read lenses to 380nm and gives a percentage transmission reading based on 315nm to 380nm."

The one we use is BPI Computer Call III.

So which is the correct portion of UV to be blocked to produce a safer lens?.IMO,up to 400nm

I has notice also that some lenses gets a more intense yelow color than others once the UV filter is applied. Even we have had a few cases where the patient returns a few week later with one or both lenses with a higher yellow color that when we dispense the lenses. This is not frequent but i would like to know why. Perhaps the wholesale lab people on here can jump in, but I think it is a batch issue. The same thing can happen when tinting lenses, where one dyes darker and faster than it's mate. The phenomena of the lenses coming back in two weeks later showing unequalo yellowing, may be due to the type/brand of UV treatment you are using. I use Chris's UV 4-in-one treatment and have never had that happen. What index are the lenses?

Looks like you already have a UV400 reading unit!

**Falstaff** · 10-26-2010, 06:41 AM

The reason for the yellowing is because a uv filter, though efficient at blocking out short wavelengths, has to become gradually less effective upon approaching the visible part of the spectrum. If such a filter takes out light at the 400nm part of the spectrum, it is removing some visible blue. When blue is removed from white light, the result is yellow. If only a small amount of visible blue is filtered out, then only a small amount of yellowing will result.