How to measure ALR screen gain - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 25 Old 01-09-2020, 12:04 PM - Thread Starter
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How to measure ALR screen gain

Hello,

Not sure if this is the right place to post this.


How can gain be measured on an ALR screen with a light meter? Screen is Cinegrey 3D.
Will compare to an A4 white paper.

Should the meter be placed perpendicular or at an angle?
This being an angular ALR, should the meter be placed between the portion of the screen measured and the eye sight of the viewer in normal viewing location?

From this report: https://www.accucalav.com/wp-content...een_report.pdf
Test Method
On Axis measurements are perpendicular to the screen
Off Axis measurements were taken 18 degrees to the side and 6 degrees down, but are of the same location as the on axis measurement point on the screen

This was recommended for measurement with the light meter facing the screen, but it may work with it facing the screen?

Quote:
Originally Posted by coderguy View Post
The proper technique when using a light meter for taking a 9-point reading is to flick your wrist back and forth until you see the highest number.
It generally takes 10-25 seconds of flicking the meter around to obtain the high number. Do this at every spot, then average them.
I rarely ever take 9-point readings, 3 is ok, but 5-point is plenty (center and all corners).

It is VERY easy to get a different reading than someone else simply by non-wrist action.
And this one from here: https://www.projectorcentral.com/Lumens-Explained.htm
you need to hold the meter with its back flat against the screen, and the sensor facing toward the projector.
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post #2 of 25 Old 01-09-2020, 03:59 PM
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Quote:
Originally Posted by noob00224 View Post
Should the meter be placed perpendicular or at an angle?
This being an angular ALR, should the meter be placed between the portion of the measured and the eye sight of the viewer in normal viewing location?

From this report: https://www.accucalav.com/wp-content...een_report.pdf
[I]Test Method
On Axis measurements are perpendicular to the screen
Off Axis measurements were taken 18 degrees to the side and 6 degrees down, but are of the same location as the on axis measurement point on the screen
On Axis measurements are made with the meter perpendicular to the screen, but the projector is also perpendicular to the screen.
EDIT: The projector was ceiling mounted in the tests, and the author noted "When a projector is mounted lower the actual gain will be higher in many cases. This is truer for the products in the high gain category than the moderate or low gain. "

Quote:
And this one from here: https://www.projectorcentral.com/Lumens-Explained.htm
you need to hold the meter with its back flat against the screen, and the sensor facing toward the projector.
That quote is for measuring projector lumens, not screen gains.

Last edited by Dominic Chan; 01-09-2020 at 05:29 PM.
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post #3 of 25 Old 01-09-2020, 05:17 PM - Thread Starter
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Quote:
Originally Posted by Dominic Chan View Post
On Axis measurements are made with the meter perpendicular to the screen, but the projector is also perpendicular to the screen.



That quote is for measuring projector lumens, not screen gains.

What is off axis measurement for then?

What distance should on axis measurements be taken from, 12-18"?
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post #4 of 25 Old 01-09-2020, 05:39 PM
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Quote:
Originally Posted by noob00224 View Post
What is off axis measurement for then?
I'm not quite sure what your question means. The report includes both on-axis and off-axis measurements; by comparing them one can tell how much the gains drops off (e.g., 33% for the Cinegrey 5D) and how much the colour shifts (e.g., xy goes up from 0.005 to 0.011 for Pearlescent.

Quote:
What distance should on axis measurements be taken from, 12-18"?
The distance does not affect the measurements, as long as you're not exceeding the meter's field of view.
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post #5 of 25 Old 01-09-2020, 06:37 PM - Thread Starter
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Quote:
Originally Posted by Dominic Chan View Post
I'm not quite sure what your question means. The report includes both on-axis and off-axis measurements; by comparing them one can tell how much the gains drops off (e.g., 33% for the Cinegrey 5D) and how much the colour shifts (e.g., xy goes up from 0.005 to 0.011 for Pearlescent.
Projector is ceiling mounted.

So I could just take a measurement with the meter perpendicular to the screen, on a screen once and on a white paper and compare the two?

Can I also take a lux measurement with the meter facing the projector and compare it to what the measurement the meter got facing the screen?


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post #6 of 25 Old 01-10-2020, 04:01 AM - Thread Starter
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Quote:
Originally Posted by Dominic Chan View Post
I'm not quite sure what your question means. The report includes both on-axis and off-axis measurements; by comparing them one can tell how much the gains drops off (e.g., 33% for the Cinegrey 5D) and how much the colour shifts (e.g., xy goes up from 0.005 to 0.011 for Pearlescent.

Still unclear on how to measure the ALR.

If measuring on axis with the meter perpendicular to the screen:
Measuring in the middle of the screen the reflective surface will send the beam on axis.
But if measuring for instance in the lower right corner, the beam reflected in the screen will not be diffused at ~160 degrees like a non ALR screen. With the meter perpendicular to the screen the measurement will be off axis.
On top of that, the viewing position is not perpendicular to the lower right of the screen, or whatever other surface other than the center, so the light that the viewer receives is even more off axis.
Which is why I asked if the meter should be placed between the area of the screen that is to be measured and the position of the viewer, to measure the gain that the viewer will actually perceive.
Is this correct?
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post #7 of 25 Old 01-10-2020, 10:37 AM
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Quote:
Originally Posted by noob00224 View Post
Still unclear on how to measure the ALR.

If measuring on axis with the meter perpendicular to the screen:
Measuring in the middle of the screen the reflective surface will send the beam on axis.
But if measuring for instance in the lower right corner, the beam reflected in the screen will not be diffused at ~160 degrees like a non ALR screen. With the meter perpendicular to the screen the measurement will be off axis.
On top of that, the viewing position is not perpendicular to the lower right of the screen, or whatever other surface other than the center, so the light that the viewer receives is even more off axis.
Which is why I asked if the meter should be placed between the area of the screen that is to be measured and the position of the viewer, to measure the gain that the viewer will actually perceive.
Is this correct?
Off-axis measurements are not taken with the meter perpendicular to the screen. In the AccucalAV report they say
Quote:
Off Axis measurements were taken 18 degrees to the side and 6 degrees down, but are of the same location as the on axis measurement point on the screen
Because the projector is ceiling mounted in their case, the off-axis gain measurements can be higher than on the axis measurements, which is very misleading.

To see how the screen behaves in your installation you should ideally take all measurements from the main viewing position, but that will likely exceed the meter’s field of view unless the meter has a very narrow angle of view. The alternative is to take the measurement closer to the screen, but still with the same angle as from the viewing position.
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post #8 of 25 Old 01-10-2020, 01:03 PM - Thread Starter
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Quote:
Originally Posted by Dominic Chan View Post
Off-axis measurements are not taken with the meter perpendicular to the screen. In the AccucalAV report they say


Because the projector is ceiling mounted in their case, the off-axis gain measurements can be higher than on the axis measurements, which is very misleading.

To see how the screen behaves in your installation you should ideally take all measurements from the main viewing position, but that will likely exceed the meter’s field of view unless the meter has a very narrow angle of view. The alternative is to take the measurement closer to the screen, but still with the same angle as from the viewing position.
Haven't measured it this way yet, but I did do some other measurements:
With the meters about 20" away from the screen, measured 6 points and averaged. Meters were perpendicular to the screen in one case and at a 45 degree angle (upwards) so the shadow would not seen.
Made a large sheet of paper from 9 pieces of A4.
For the 45 degree method, the white paper was 40% brighter than the screen, and for the perpendicular method it was 42% brighter.
LE: the lux values in this test ranged between 35 and 130 lux.

Which would make the screen 0.6 gain. The claimed gain is 1.2. The Cinegrey 5D measured 33% less in the report, from 1.5 to 1.0.

While doing the tests, I've ran into another problem:
Quote:
Originally Posted by noob00224 View Post
@NxNW
Did some measurements with two light meters. One registered 15% higher than the other (URCERI MT-912>LX1010B(big sensor)).

Waited about one hour after projector startup. Cinema, BC off, 1.5x, SmartEco, gamma Benq, Full RGB but contrast/brightness is set to 16-235. 327h total, 100h Full, 227 SmartEco. Lights off, no other light sources, night time. Projected a white field.
Measured 5+1 points, center, each corner, and lower left from the center. Also tried the meters around the screen to check for brightness variance, but these were enough.
Placed the meter with the back on the screen.

The difference (with the projector in the same place) between no zoom and 100% zoom (focused) is 30% (less). Model is W2000. It supports the claim that the W2000/HT3050 looses ~30% of light when zooming out.

Brightness was not uniform with the edges around 30% less bright than the center.
There is an area to the lower left of the center that measures 20% higher than the center.

When I took some pictures I originally thought it was because the fabric was not smooth:
https://www.avsforum.com/forum/23-sc...l#post58659830

LX1010B average 160lux
90 000 lux at lens

MT-912 average 180lux
92 000 lux at lens

lumens = (lux / 10.76) * square feet of screen
106" screen = 33.37 ft²

496 lumens or
558 lumens

Something isn't right, it's too low, should be double.

LE:
Changed the gamma to 2.2. and lamp to Full but same results.
BC increased the output by 25%.

LE2:
Measure the monitor (Dell 2209WAf) rated at 300 nits.
Averaged 264 lux, square surface is 1.52 ft².
Results in 37fL, or 126 nits.

Am I doing something wrong?

Last edited by noob00224; 01-10-2020 at 01:24 PM.
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post #9 of 25 Old 01-11-2020, 05:53 AM
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Sanity check:. What do you mean by "meter"?

Meters that measure light coming *from* a screen have a light gathering objective that looks like a traditional camera lens. Shiny glass. They have names like colorimeter or spectrophotometer.

Meters that measure incident light falling *on* a screen have a white plastic diffuser that is intended to collect ambient light from all directions (and weight it according to a specific cosine function). This kind of meter would include your typical "lux meters"

You can't use an incident light lux meter to measure light coming *from* a screen. I mean you physically can, you'll get a reading, but it can't be used in any kind of formula that was expecting a direct (non diffused) measurement as an input.
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post #10 of 25 Old 01-11-2020, 01:33 PM - Thread Starter
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Quote:
Originally Posted by NxNW View Post
At first glance I don't see anything too crazy. If the W2000 is 11.5' away from the nearest edge of the screen you should get a peak of over 300 lux at the brightest region of the image. Maybe even 350. Try the technique coderguy mentioned, do not just hold the meter oriented with the enclosure pressed flat against the screen, try angling it to face the lens itself, and continue adjusting the orientation until you get the highest possible reading at that location.

Oh and when I saw the remark about using a lux meter on a Dell monitor, I realized there may be some misunderstandings about the difference between luminance and illuminance. I replied over in that other (ALR) thread you linked to. Short answer: for our purposes, a lux meter is only ever pointed at the lens of the projector, never the screen.
The MT912 has more of an enclosed sensor (the 1010B it's exposed) can't it be used for measuring the monitor if placed as close as possible to the screen?


Used the wrist with the meters instead of keeping them flush against the screen but the increase of small, for instance 196lux vs 190 previously.
The center measures 196 (238 on the MT218) and the brightest part which to the lower left of the center has 244 (282). I don't know which meter is accurate. @coderguy tested a LX1010B a while back with some better meters and found it ok.

Projection dream and Projector central both measured the W2000/HT3050 and got around 1200lm with 100% zoom in Cinema Full lamp. The other reviews had similar or higher measurements:
https://www.avsforum.com/forum/68-di...l#post58860670

Lumen values right now, with the average of center, four corners, and the bright spot make 179lux and 213lux for the MT218, or 555lm/659lm.

The light loss from zooming out from two calculators (HT3050 with PC and WebC) is 26% and 21%.
Didn't move the projector. Took readings just in front of the screen.
After that zoomed to 100%. Took a piece of paper where an 106" screen would have been (8'10"/270cm) and (after focusing) took readings at the height where the center of the screen would have been (same height as the current screen).
Loss of light was 20% on one meter and 17% on another. Average 18%.
So definitely not 5, 9 or even 27%. WebC was closest. Makes you question all the measurements found online.

327h is 225 equivalent in Full lamp. That's about 12% brightness loss. 1200lm at 0% zoom is 984lm. Let's say the lamp lost 12% brightness, 865lm.
That is still 30% more than the 607lm (555/659) averaged. Even with the meter that read's the higher lumen, 659, that's 24% more.
WebC with 200h and 10% brightness loss, at 1.5x, in Full lamp Calibrated the result is 489 lumens.


Can dust inside the light path affect brightness?
What about refresh rate/color wheel rpm? There was no noticeable difference between 23 and 60Hz.

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post #11 of 25 Old 01-11-2020, 05:50 PM
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Quote:
Originally Posted by noob00224 View Post
Took a piece of paper where an 106" screen would have been (8'10"/270cm) and (after focusing) took readings at the height where the center of the screen would have been
Not to belabor the point, but you are only collecting data obtained while white plastic is facing the lens right? I'm a little confused as to the need for paper in the plane of a virtual screen? Unless maybe you were using it to focus? Honestly I don't think small variations in focus will change the outcome much.


Ok let's take it from the top.



Light meters that measure light coming from the screen are built like cameras. They have a limited, well characterized field of view. They generally require software to interpret the values coming down the wire. They report on both the quantity and quality of light, ie they can tell you which color they see. With enough math, you can distill these complicated readings into a single number related to "how much light hit the meter". The software being used to interpret the meter's output can report this number easily. The unit will be nits. As long as the bright area being measured uniformly fills the device's field of view, you will get the same value no matter how far you are from the thing you are measuring.



Light meters that measure light coming from the projector lens are built differently. They often have a white plastic diffuser dome or disc. They have a very non specific 180 degree field of "view". These meters report only on the quantity of light, not the quality. They cannot tell you what color they see. They report only a single number related to "how much light hit the meter". They require no additional software to arrive at this number, it's usually reported on a little LCD display. The unit is lux. The further the device is away from the source, the lower the value (and the outcome will be very sensitive to even small differences, according to the inverse square law).



Lux and nits are not the same physical concept. If you make certain assumptions (like a perfectly diffuse lambertian reflecting surface with a gain of exactly 1 etc) you can *sort* of calculate how much of one you would get from a certain quantity of the other. But just understand they are fundamentally different physical quantities.



Same goes for converting lux to lumens. Lux is directly measured. Lumens are computed, and once again such a computation requires making a lot of assumptions. (To directly measure lumens you need a light integrating sphere which is a pretty formidable looking device. It sure aint a ten dollar lux meter).


Moral of the story, don't point a lux meter at a screen. It is always meant to be oriented with the diffuser facing a point source of light such as a candle, projector lens, light bulb or the sun.
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post #12 of 25 Old 01-11-2020, 06:10 PM
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The Minolta T-10 is the reference LUX meter used in this industry by pretty much everyone, not sure about light integrating spheres. Some of the Sekonics would be a close second. LUX meters are only useful for standing at the screen with your back to the screen and then pointing the meter at the projector's beam of light. The reason you must use the wrist flicking trick is mainly for the edges of the projector's beam (it helps with the center reading some), but generally it can make a huge difference at the edges.

This is because LUX meters have a weakness in that if you are the edge of the light path (hence back near edge of screen), then the LUX meter will get a bad reading because the light isn't as FULL in the LUX's sensor angle as far as it being projected when standing in the middle of the projector's light path. Also, unless you hang the LUX meter on a pole and stand out of the projected light path, the other issue is your shadow cast is reducing the lumens some (more so in a non-bat cave), because LUX meters have very wide angle sensors and also pick up reflected light due to imperfect angular errors, which is why they cannot be used to measure off the screen after the light is reflected.

The only way to actually know for sure your getting an accurate reading is to use a certified Lux meter, and they are expensive. The second best way is to use a few different types of meters and try to find the weaknesses in your own setup.

The first thing anyone has to do when using a cheap LUX meter is make sure it's ballpark, some can be way off. I would measure a neutral gain material on the screen (a piece of paper) with a colorimeter and compare that to your converted center LUX reading from the light meter (again we aren't measuring the screen with LUX meter, only projection beam, but what I mean is compare screen vs. beam measurement after conversions are done). I wouldn't expect these to be exact, but it should be close.

Get a used Spyder Meter on Ebay for the colorimeter side to take a direct off-screen reading, not sure how accurate it is but I think it's ok. I can compare later, I have one laying around. I use the C6 for off-screen readings. I don't necessarily think all cheap 1010's were close, just had a couple and they were ballpark > 15% error. I also have a lx1030b (it was way way off by 50%).

Anyone can use my calculator (webprojectorcalculator.com) to convert between the measurements by using the convert tab, no math is needed. There is a very small rounding error (under 2% I think, forget), simply because I didn't code every possible rounding type into the converter. My calc automatically handles every variable (hence screen size for LUX to Lumens, but ignores gain as proper), so that way you know you aren't making a mistake in the math.

**Updated Projector Calculator Released NOV 2017**
-- www.webprojectorcalculator.com --

Last edited by coderguy; 01-11-2020 at 06:39 PM.
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post #13 of 25 Old 01-11-2020, 06:28 PM
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Quote:
Originally Posted by noob00224 View Post
Can dust inside the light path affect brightness?
What about refresh rate/color wheel rpm? There was no noticeable difference between 23 and 60Hz.
Dust can definitely reduce the brightness significantly, but the most common issue is variances in lamp quality and output. The lamps that come with the projectors are usually 'golden samples', and depending where you bought your lamp, even if it's the REAL DEAL and a completely valid original and not a fake, well it can still be significantly dimmer.

Another problem is the projector market is flooded with USED lamps pretending to be NEW, especially this problem is VERY BAD for DLP lamps. The scam is that some companies claim to be able to recycle lamps, so they buy 'used lamps' in bulk and then put them back onto the market through Ebay channels. So you buy a lamp and it's actually used.

These companies "recycling" these lamps, some of them have huge operations. They buy thousands of lamps at once from govt surplus or other sources. Since many Benq projectors have some commercial equivalent projectors using the same lamp as their home theater cousin, then these dishonest recycling shops are able to buy thousands of used lamps at once and flood them into Ebay channels.

It's real annoying.

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post #14 of 25 Old 01-11-2020, 08:16 PM - Thread Starter
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Quote:
Originally Posted by NxNW View Post
Not to belabor the point, but you are only collecting data obtained while white plastic is facing the lens right? I'm a little confused as to the need for paper in the plane of a virtual screen? Unless maybe you were using it to focus? Honestly I don't think small variations in focus will change the outcome much.

Moral of the story, don't point a lux meter at a screen. It is always meant to be oriented with the diffuser facing a point source of light such as a candle, projector lens, light bulb or the sun.
Yes, with the meter's sensor facing the lens.
Wanted to focus the image on the paper.

Not the projector screen, the monitor screen. It's source of light (?).


Quote:
Originally Posted by coderguy View Post
The Minolta T-10 is the reference LUX meter used in this industry by pretty much everyone, not sure about light integrating spheres. Some of the Sekonics would be a close second. LUX meters are only useful for standing at the screen with your back to the screen and then pointing the meter at the projector's beam of light. The reason you must use the wrist flicking trick is mainly for the edges of the projector's beam (it helps with the center reading some), but generally it can make a huge difference at the edges.

This is because LUX meters have a weakness in that if you are the edge of the light path (hence back near edge of screen), then the LUX meter will get a bad reading because the light isn't as FULL in the LUX's sensor angle as far as it being projected when standing in the middle of the projector's light path. Also, unless you hang the LUX meter on a pole and stand out of the projected light path, the other issue is your shadow cast is reducing the lumens some (more so in a non-bat cave), because LUX meters have very wide angle sensors and also pick up reflected light due to imperfect angular errors, which is why they cannot be used to measure off the screen after the light is reflected.

The only way to actually know for sure your getting an accurate reading is to use a certified Lux meter, and they are expensive. The second best way is to use a few different types of meters and try to find the weaknesses in your own setup.
.

How long should the pole be? Should I just not be in the light rectangle?
Should it still be wiggled around? That's sort of difficult while attached to a pole or a tripod.
The two meters are URCERI MT-912 and HDE LX1010B.
The MT912 has a wall around the sensor, so can I just sit to the side while holding it?
The HDE has a large sensor without a wall.
A colorimeter is in the works soon.

The new lamp is directly from Benq, installed by them after servicing and cleaning.
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Quote:
Originally Posted by noob00224 View Post
Not the projector screen, the monitor screen. It's source of light (?).
Nope. Although a computer monitor does emit its own light, the key difference is that it is the thing you are looking at. The brightness of a visually interesting surface is measured using nits.

Lux comes from point sources like lamps whose primary function is to light up other things that get looked at. They themselves are not fun to look at.

A monitor is directly looked at. It is not used as a flashlight.

Lamps illuminate. They produce a measurable quality called illuminance.

Screens are luminous. They produce a measurable quality called luminance.

Illuminance is not the same as luminance.

One key distinction is surface area. The concept of luminance requires there to be some amount of surface area. The unit we call a nit is actually cd/m2 so there's a clue surface area is involved. Monitors have surface area. They are measured in nits not lux.
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Quote:
Originally Posted by noob00224 View Post

How long should the pole be? Should I just not be in the light rectangle?
Should it still be wiggled around? That's sort of difficult while attached to a pole or a tripod.
The two meters are URCERI MT-912 and HDE LX1010B.
The MT912 has a wall around the sensor, so can I just sit to the side while holding it?
The HDE has a large sensor without a wall.
A colorimeter is in the works soon.

The new lamp is directly from Benq, installed by them after servicing and cleaning.
You don't need a pole, I was just giving an illustration.

The piece of paper was so that you could measure the light at 1.0 gain with the colorimeter, nothing else. Otherwise you'd be comparing your LUX meter to a colorimeter reading with a modified screen gain measurement, which is going to be ever farther off. With a colorimeter, it is a lot more trouble to get an accurate measurement, requires you to keep re-positioning it to get the highest fL from the tripod position. Some colorimeters have less error than others when it comes to this step. Plus, when measuring off the screen you're getting a modded measurement from the screen's surface, so that is why the Lumens and LUX are more commonly used as a measure with a lux meter because it is a universal measurement without being modded by the screen.

Nits and fL are measured off the screen, they are the same type of measurement, just a different ratio.
Lux (Lumens after conversion) is measured towards the light source.

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Last edited by coderguy; 01-11-2020 at 11:12 PM.
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post #17 of 25 Old 01-12-2020, 04:30 AM - Thread Starter
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Quote:
Originally Posted by coderguy View Post
LUX meters are only useful for standing at the screen with your back to the screen and then pointing the meter at the projector's beam of light. The reason you must use the wrist flicking trick is mainly for the edges of the projector's beam (it helps with the center reading some), but generally it can make a huge difference at the edges.

This is because LUX meters have a weakness in that if you are the edge of the light path (hence back near edge of screen), then the LUX meter will get a bad reading because the light isn't as FULL in the LUX's sensor angle as far as it being projected when standing in the middle of the projector's light path. Also, unless you hang the LUX meter on a pole and stand out of the projected light path, the other issue is your shadow cast is reducing the lumens some (more so in a non-bat cave), because LUX meters have very wide angle sensors and also pick up reflected light due to imperfect angular errors, which is why they cannot be used to measure off the screen after the light is reflected.

Not sure if I understand. For measuring the light beam directly, I need to be between the meter and the screen?
Placing the meter closer to the projector would increase the lux value.
Measured it holding it to the side.
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post #18 of 25 Old 01-12-2020, 07:14 PM
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Quote:
Originally Posted by noob00224 View Post
Not sure if I understand. For measuring the light beam directly, I need to be between the meter and the screen?
Placing the meter closer to the projector would increase the lux value.
Measured it holding it to the side.
You need to be standing directly in front of the screen, with your back almost touching the screen, with the LUX meter pointing toward the projector's light beam. The meter should be at the same distance as the screen itself, otherwise you'll get too high of a reading.
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post #19 of 25 Old 01-12-2020, 10:18 PM - Thread Starter
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Quote:
Originally Posted by coderguy View Post
You need to be standing directly in front of the screen, with your back almost touching the screen, with the LUX meter pointing toward the projector's light beam. The meter should be at the same distance as the screen itself, otherwise you'll get too high of a reading.
That's how it was done.
From the previous quoted post, I understood that me sitting there to the side of the meter holding it would affect the reading since it's picking up a darker object than the screen (me).
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Originally Posted by noob00224 View Post
That's how it was done.
From the previous quoted post, I understood that me sitting there to the side of the meter holding it would affect the reading since it's picking up a darker object than the screen (me).
It just depends, you just have to be careful to try to get the highest number in all cases.

It mainly happens if you are blocking the beam itself, but yes the cheap lux meters will be way off for the edge readings in the full 9-point tic tac toe ANSI Lumens measurement, so your uniformity would appear to be worse using a cheap LUX meter than it really is.
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Last edited by coderguy; 01-12-2020 at 11:37 PM.
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post #21 of 25 Old 01-14-2020, 08:33 PM - Thread Starter
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Originally Posted by SirMaster View Post
MLP is just a HT term people seem to use for main listening position. I guess it applies for audio but why not video too since it's the same position in a home theater. It just means the main seat.

According to the specifications for the i1 Display Pro, the viewing angle is 160 degrees. So you would need to calculate that from the distance.

https://keisan.casio.com/exec/system/1273850202

Use the height and vertex angle option and the vertex angle is 80 and the height is the meter distance.

Quote:
Originally Posted by noob00224 View Post
I can only find this info regarding angle:
Ambient measurement angle: 160 degrees cosine response
http://www.vpixx.com/datasheets/ds_i1display_pro.pdf

Is the 160 degrees vertical or horizontal?

LE: for an 106" (16:9) screen in order for the field of view not to exceed the screen it needs to be placed at 20.7cm/8.14" on the center axis. Isn't this too close?
I'm not sure how the meter will react if it's placed at the MLP (320cm/10.5').

LE2:
Would a velvet tunnel work?
I've sent an email to X rite but haven't received an answer yet.

I think I saw a velvet tunnel in one article, the Projection Dream contrast and room treatment. Was thinking of making a rectangular 16:9 box with velvet on the inside so the meter would just pick up the screen.

@Dominic Chan the Silver Ticket High Contrast Grey has some ALR properties, how was the gain measured?
With a X Rite type colorimeter if the lens is placed upwards at an angle so the shadow is not seen, the angle would not be the same as the viewing position. Since ALR screens, depending on model have different vertical half gains, this method would result in a lower gain than from the seating position.

Even if the X Rite would be placed closer and multiple measurements were taken in different areas of the screen to avoid the 160 degree angle, the ALR properties make it difficult go get an accurate reading.

Anyone experimented with this type of measurement? Are there specialized tools required?
I'm new at this and not sure of how things work. Any insight would be helpful.
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Originally Posted by noob00224 View Post
I think I saw a velvet tunnel in one article, the Projection Dream contrast and room treatment. Was thinking of making a rectangular 16:9 box with velvet on the inside so the meter would just pick up the screen.
The velvet tunnel is used for measuring high contrast ratios, so that the black areas can be measured without picking up the stray light from the bright areas. It’s totally unnecessary for measuring screen gains.

Last edited by Dominic Chan; 01-15-2020 at 08:44 PM.
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Originally Posted by Dominic Chan View Post
The velvet tunnel is used for making high contrast ratios, so that the black areas can be measured without picking up the stray light from the bright areas. It’s totally unnecessary for measuring screen gains.
So how would one measure the screen gain, or nits value of an ALR?
Wouldn't placing the colorimeter at the seating position also pick up the area outside the screen?

LE:
Quote:
Originally Posted by Dominic Chan View Post
The angle of view of the i1Display Pro is way narrower than that, at about +/-5 degrees. 160 degrees is for the ambient light mode, when the diffuser is placed in front of the measuring lens.
This would make it a lot easier.

Last edited by noob00224; 01-14-2020 at 09:22 PM.
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Quote:
Originally Posted by SirMaster View Post
According to the specifications for the i1 Display Pro, the viewing angle is 160 degrees
The angle of view of the i1Display Pro is way narrower than that, at about +/-5 degrees. 160 degrees is for the ambient light mode, when the diffuser is placed in front of the measuring lens.
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post #25 of 25 Old 01-17-2020, 04:27 PM - Thread Starter
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Quote:
Originally Posted by Dominic Chan View Post
The angle of view of the i1Display Pro is way narrower than that, at about +/-5 degrees. 160 degrees is for the ambient light mode, when the diffuser is placed in front of the measuring lens.
Send X Rite an email with the specification of the screen being an ALR with a hotspot:

Place the tripod and with the device attached in front of the projector screen at a distance of 1.5 times the height of the projected image away from the screen, with the device's lens pointing towards the centre of the screen.

Adjust the height of the device on the tripod so it shows up as a shadow at the base of the projected image on the screen. Adjust the device's angle so it point towards the centre of the screen and run the calibration.

LE:
The angle of the X Rite i1Display Studio, i1Display Pro, ColorMunki, and probably others on the same chassis is 60 degrees horizontaly.

What about a (possibly) positive gain alr screen with a hotspot?

You can compensate for screen issues when taking off-screen readings by measuring all the different points, problem is the math involved allows for a lot of error. It would be more trouble than it's worth and most of the compensation math I've seen isn't sufficient in how people try to calculate it.

LE2:
Hanged the meters with a string but still flush to the screen, with no one holding them, the reading were the same.

Last edited by noob00224; 01-21-2020 at 03:17 PM.
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