How does this work?

[frankieb]

Steve,

Since I can't seem to find this answer by searching, I'm just gonna ask...

I was looking at the Cosmedico catalog the other day and the 160W 9K90's say the following:

UVA Flux - 40.3
UVB Flux - 0.5
Total UV - 40.8

How does that translate into a meter reading? Should I be able to meter a new, broken in lamp and get these readings on the 5.0 and 6.0?

[solarmeter®]

I've never liked the way Cosmedico does that because nobody understands "flux". They measure it by putting the 6-foot lamp into a giant white ping pong ball like this:



Details on how it works here: www.olinet.com/products-intergrating_sphere.php3

The flux values are radiance not irradiance. Radiance is W or mW or µW along the entire surface of the lamp shining on the ping pong ball walls. I believe the above values are W (watts).

Irradiance (like the UV meters read) is W or mW per a unit area like m² or cm².

The flux and irradiance values will never match - but they ARE proportional. So you can figure percent UVB from the Cosmedico site... but the meter readings will be per square centimeter of skin exposed not Watts of UV in a white sphere.

As Don might say.... hope that helps.

PS: In theory you could calculate "watts flux" from a single lamp in air by taking a meter reading in mW/cm² times how many square centimeters the lamp has divided by 1000 (there are 1000 mW in a W). But who would ever bother doing that?! Or buy a $50K ping pong ball haha.

[frankieb]

.... hope that helps.

Oh yeah, crystal clear now...

So, essentially the UVA Flux - 40.3, UVB Flux - 0.5, Total UV - 40.8 don't mean a whole hell of a lot to your average salon owner?

I didn't know if there was a way to get a "baseline" reading on lamps using these numbers. For example, let's say you just bought a used bed with the 160W 9K90's that had 700 hrs on the lamps. Is there a way to determine current degradation? Or, do you just roll the dice and use the scientific method of "I ain't getting as much color as I used to"?

[solarmeter®]

I once knew a guy named Jerry Frank from Cosmedico (in the US) who could probably answer that.... but I lost his contact info over the years. I'll email this thread to D. Smith and maybe he will chime in.

If there IS a way to correlate those flux values with meter readings... it would have to be based on a single lamp comparison. Not one in a ping pong ball vs 20-some in a canopy.

The 40.8W of A+B flux basically means that from 160W input there are 40.8W of UV output. So the lamp is 40.8/160 = 25.5% efficient at making UV light. I think.

Even if all the mfgrs listed irradiance in mW/cm² (like a Solarmeter sees) it would be for a single lamp at a certain distance (like 10cm) with a standard ballast current, break-in "seasoning" time, temperature, etc.

When you have a bed full of lamps the body position readings are 3-4 times higher than a single lamp. You can see that by holding meter against acrylic vs at belly button position with canopy closed.

All this (and more) is why lamp makers and sellers resist publishing ANY specific output numbers. A standard test protocol was presented by Don many moons ago... but it was like herding cats!

[frankieb]

I can understand why there would be resistance, then you would be able to compare, in theory, apples to apples. That would be bad.

So, ultimately, there is no accurate way to determine lamp degradation if you do not have base readings to start out with. Obviously there would be differences with reading a 12 lamp canopy vs. a 20 lamp canopy. It's just a crapshoot until your lamps go south.

Thanks, Steve.

[solarmeter®]

For example, let's say you just bought a used bed with the 160W 9K90's that had 700 hrs on the lamps. Is there a way to determine current degradation?

Yes... put two new 9K90's in adjacent to each other on the same ballast and compare their "at lamp" readings to the ones with 700 hours.

See the third "Q" here: Welcome to Solartech

Also.... it just dawned on me how you can relate those Watts-flux values with mW/cm² meter readings on the two "new" 9K90's: With a 5.0 meter in middle of lamp... keep pulling away from it until it reads 40.8. And with a 6.0 meter do the same until it reads 0.50.

Record the distance away from lamp that you get those numbers. That becomes your baseline for checking any other used 9K90 lamps with hours on them. The older they are the closer you will need to meter them to get the same values. If you have to go 30% closer that means they are 30% shot. But if you only have to go 10% closer that means they have 20% more degradation to go.

So there: I "figgered" it out without Don Smith's help lol.

[Don]

My "buddy" Frankie has become a "meter geek" and I am still in shock.

I have never liked the way Cosmedico presents their data because (IMHO) it doesn't look very impressive.

The best way I have found is to remove all but one or two lamps from a bench or canopy and compare the new lamp to the old one. I like the Model 7.0 MED/hour meter best for this test.

Or, Frankie, you can do like a salon owner once told me. Wait until the third client complains and then order new lamps.

[frankieb]

Also.... it just dawned on me how you can relate those Watts-flux values with mW/cm² meter readings on the two "new" 9K90's: With a 5.0 meter in middle of lamp... keep pulling away from it until it reads 40.8. And with a 6.0 meter do the same until it reads 0.50.

Now that's an interesting approach using the flux numbers. You would wonder if the optimal distance to hit those numbers would be around belly height?

My "buddy" Frankie has become a "meter geek" and I am still in shock.

Don, I'm not 100% sure, but I think you're probably talking about Frankie (female) not FrankieB (male). Nice to see you here anyway.

[solarmeter®]

You had us both fooled... thought you were Frankie Burrel(sp)..... female.

I emailed Cosmedico asking them to respond to this thread. Fat chance - but we'll see. Hopefully they will chime in... because they are a great company with lots of scientific resources in the EU. And they are one of the few who take UV lamp "compatibility" quite seriously.

[solarmeter®]

Cosmedico did respond. Here it is:

Feel free to post my response, and thanks again for allowing us to share our opinions.


Kevin

On Aug 19, 2008, at 10:26 AM, Steve Mackin wrote:

Kevin,

OK - thanks. I understand.

Do you mind if I post your response on the "blog" thread? The important part is that such flux numbers should be used in reference to other Cosmedico lamps as a relative comparison.... not to UV meters and/or other mfgrs lamps.

Steve

----- Original Message -----
From: Kevin Apgar
To: solarmeter@comcast.net
Sent: Tuesday, August 19, 2008 10:15 AM
Subject: Fwd: Flux vs Irradiance


Steve, Thank you for providing us the opportunity to respond to this inquiry.
You are almost correct; we do not do our measurements in a ping pong ball, but a "black" room with precise temperature monitoring and control ballasts. Unfortunately the numbers we provide will not compare directly to a meter reading for many of the reasons already discussed in the thread. There are many control factors at the salon level that we can not account for such as voltage variances, age/transmissivity of acrylics, ambient temperature, ballasts employed, number of lamps in the array and so on. As a result it is very difficult for Cosmedico to flat out state how we would expect our lamp to read on a Solarmeter. Our goal with providing UV Flux is to serve as a comparison amongst the Cosmedico products in our catalog and how they differ from each other. While we do have readings mW/cm2 they are for single lamps not arrays. These measurements are very important in our manufacturing process as they are the benchmark with which we compare our lamps to manufacturing specifications as well as monitor competitive products.


I hope this helps to clear up our position on why we use our Flux values in the catalog.


Thanks,
Kevin Apgar
VP Sales & Operations
Cosmedico Light, Inc.