JVC 2011-2012 lamp measurement project - Page 4

The LX1010B specifies accuracy of +/- (5% + 2d). So, for a 20lux reading, the lowest digit is 1 lux, so 5% of 20lux + 2d = 1lux + 2lux = 3lux. Which gives us 20+/-3 lux accuracy.

Well, I trust it to be accurate within 3lux at a reading of 20lux. But the main point is that his old projector appears to be measuring nearly 10x lower than what most people would consider an optimum brightness level. Surely you are not implying that the reading of 20lux is inaccurate by a factor of 10 too low? There is just no way it is off that much. Even a factor of two (40lux vs. 20lux) is very hard to believe.

Unless you have some real evidence of inaccuracy, I trust the spec, which says at 20 lux it is accurate to +/- 3lux.

Please provide a link to a post or posts that shows convincing evidence that the LX1010B or a similar meter are not as accurate as they are specified to be.

It is a lot of work to find even one post that you claim provides evidence that the LX1010B meter, or one like it, is not as accurate as it specifies? Really?

I think I will take the specifications from the meter manufacturers over some elusive evidence that only you know of but cannot reference.

You gave no evidence that the accuracy of the LX1010B meter, or one like it, is worse than the manufacturer's specification.

Basically, you gave a convoluted description of your interpretation of some measurements that seemed inconsistent, then jumped to the conclusion that some meters were not as accurate as claimed. That is not evidence. It is wild conjecture.

It takes persuasive evidence to prove that a manufacturer's specification for their meter is wrong. You have not provided any evidence at all. Your claims are spreading FUD (fear, uncertainty, doubt) without having any substance.

As I said, the accuracy specifications from the meter manufacturers are far more trustworthy than your unsubstantiated conjectures.

If you wish to debate this issue further, please take it to PM, or another thread. If you had linked to actual evidence, I would not have a problem with your posts in this thread. But as long as you are spreading unsubstantiated conjecture, I think it is only cluttering up this thread and causing confusion.

Lux (lumen / meter^2) is a unit of illuminance and is a photometric quantity, which means that the power in each wavelength is weighted by the sensitivity of the human eye to that wavelength.

In contrast, Watt / meter^2 is a unit of irradiance and is a radiometric quantity, using absolute power without weighting by wavelength.

The bottom line is that the accuracy specification of an illuminance meter includes both the weighting by wavelength as well as the energy of the incident light, whatever the wavelength.

EDIT:
coderguy provided a link showing that some AEMC meters have worse accuracy on "common light" than 2856K (tungsten filament) light. The question is how much the filtered arc-lamp light from a projector differs from 2856K light.

Thanks for the link.

So the worst case for those AEMC meters is 18% +/- 2 counts. If the CA811 were reading 20lux on the 200lux scale, one count would be 0.1lux. So the accuracy would be 18% of 20 + 0.2 lux = 3.8 lux.

As you say, the CA811 is a more expensive meter than the LX1010B. So the implication is that if the CA811 is only accurate to 18%, then the LX1010B should not be more accurate than 18%.

So let's round it up to 20% for the cheaper LX1010B.

20% of 20lux + 2digits = 4lux + 2lux = 6 lux.

20lux +/- 6lux gives a maximum of 26lux, which comes to 93 lumens for a 114 inch screen. Which is obviously still quite dim.

Because high accuracy is not really relevant to the JVC lamp project. For this project, accuracy is not as important as repeatability and linearity, which are fine with the LX1010B. We are trying to answer a question about lamp dimming. We do not need to know whether the lumen measurement is accurate compared to a more expensive meter, only how much the measurement changes as the bulb ages.

Accuracy only came up here as to whether the meter was in the ballpark or not , i.e., whether it was reading 10x too low. Since that is well outside of any conceivable accuracy specification, then if it really were reading 10x too low, it would be a defective meter. But my guess is that the meter is okay, and the projector is just dim.

But feel free to compare the meters you own at 20lux (as measured by the most expensive one) and see how closely the cheaper one(s) compare. But if you do, please start another thread, since it is not very relevant to this thread.

Please sign up now for the JVC lamp measurement project! Just post in this thread or PM me to sign up.

You can sign up now even if you won't be able to make any measurements until January.

We have 32 participants signed up for the project so far, but we need more people. I'd like to reach at least 50 people, and 100 would be even better!

Deadline to sign up is Friday, 9th December. Only 48 hours until the deadline!

X90, cool! Thanks for signing up!

So I can sign you up for the project?

Thanks for signing up!

I am not familiar with "The Source". Did you see post #7 in this thread with several light meter recommendations? There are links to google shopping with several vendors to buy the light meters.

Thanks for signing up! What model do you have on order?

The initial sign-up deadline has passed and we now have 40 people participating in the project! But I was hoping to get at least 50 participants, and more would be better, so I am going to extend the sign-up deadline.

Extended sign-up deadline: Friday, 16th December

If you have a new 2011-2012 JVC projector, or expect to have one by the end of January 2012, please sign up now! To sign up, you can PM me or post in the project thread:

http://www.avsforum.com/avs-vb/showt...4#post21276994

Participating in the project should only take a few minutes of your time each month.

If you don't have a light meter, you can order a cheap one online. See post #7 for recommendations.

For reference, I copied down most of the text I could find on the lamp or lamp-housing from my RS45.

On the housing:
JVC 220W
Model: PK-L2210U
>PPS<<br /> CMX22283

On the lamp:
83 (in pencil on vacuum epoxy seal)
OT 723093JJ5 (or could end in 005, some ink was maybe missing)
QLL0194-003
PC010632399
HSCB220V2H