Tint Meter
Training Manual For
Law Enforcement Officers
Laser Labs, Inc.
454 First Parish Road, Scituate, Massachusetts 02066
Table of Contents:
D. Interpreting The Model 100 Tint Meter™ Readings
D. Interpreting The Model 200 Tint Meter™ Readings
IV. Basic Information on Window Film
ãLaser Lab, Inc., 2001
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the authors.
Laser Labs, Inc., published by arrangement with the author.
First printing, January 2001
Printed in the United States of America
fig. 1 Tint meter Model 100™ photo
General
The Tint Meter Model 100™ is a hand held device manufactured by Laser Labs, Inc. of Scituate, Massachusetts that measures the amount of light that passes through a window. It measures the total amount of Visual Light Transmission (henceforth referred to as VLT) through a window and any coatings (tint film) on that window. The device was designed, as an affordable way for law enforcement officers to measure the total VLT of a window after it has been treated with aftermarket window film. The device slides over a partially rolled down window, does its calculations, and in seconds displays the readings on a liquid crystal display (LCD). Because it has its own internal light source, the meter will work day or night.
Physical Characteristics
The Tint Meter Model 100 is housed in a plastic enclosure. The enclosure is 5.25 inches tall, 3.5 inches wide, and 1.5 inches deep. On the front is a label noting the manufacturer, the model number, performance specifications and some simple directions. There is a clear window on the label to view the LCD readout. A section 3 inches high, and one quarter of an inch wide has been cut from the housing, slightly off-center, to allow for glass to be slid up into the body of the Tint Meter. This section has been covered with a foam gasket that has been cut straight up the middle to allow for the glass to be slid into the meter and not be scratched by the plastic housing. On the back side of the Tint Meter is a 9 volt battery compartment.
How to perform a test
Always make sure that the area of the window to be tested is clean and free of scratches. Dirt and scratches can have an effect on the accuracy of the meter reading. The window should be inspected on both sides for cleanliness. If necessary, wipe the window with a soft cloth to remove dust etc. If you are not sure about the reading remove the meter and take a second reading from a different spot on the window. Be sure to follow the instructions below in order to prevent damage to your meter.
On a door where there is a full frame around the window, roll the window down far enough for the Tint Meter to fit in between the glass and the window frame. On doors where the window is not framed in on the top, you do not have to roll the window down, but instead open the door. With the Tint Meter positioned vertically over the window and the foamed cut out directly over the window, press the meter down (figure 2) until the top of the cut out hits the top of the window. Remove your hand from the meter, and read the number expressed on the display (figure 3). This number represents the amount of visible light transmitting through the window. To remove the Tint Meter, lift it vertically off the window. Because there is not an external power switch , it is not necessary to manually turn the device on or off. This protects against battery drainage. Repeat this procedure to perform additional tests.
figure 2: Correct method of figure 3: Model 100 correctly
placing Model 100 on Window. Seated on roll down window.
Please note: You should never drag the meter across the window horizontally. This can damage the internal switch. If you are trying to take a reading on a different area of the window slide the meter vertically up off of the window and move it over to the desired area of the window and then place it down vertically over the window and take the second reading. This will prevent switch damage. Also, the meter reading locks after a few seconds and will not change if it is dragged across the window. The reading will hold until the meter is removed and the switch turns off, thus clearing the memory. Further, when inserting the reference samples into the meter to verify its’ calibration, the samples should always be inserted from the bottom of the meter, just like a car window (see figure 4 below). Inserting them through the face (the surface with the decal and LCD screen) can also damage the switch (see figure 5 below).
figure 4: Correct Method for figure 5: Wrong Method for
Inserting reference samples. Inserting reference samples.
When a Tint Meter Model 100™ is slid over a piece of glass it measures how much light is able to penetrate the surface of that glass and pass through to the other side. It does this by electrically measuring the brightness of light.
When the glass is slid into the Tint Meter, it activates an internal switch, located at the entrance port. This switch activates the power from the battery and sends it to a light emitting diode (L.E.D.). The L.E.D. lights up and shines a beam of light onto a photodiode. The photodiodes in turn, produces an electrical current from the light. Because the L.E.D. does not fluctuate in brightness, the output of electrical current from the photodiode remains constant and will give a reading of 100% light transmission. This turn on feature takes a fraction of a second to perform, and is the auto-calibrating sequence of the Tint Meter. ( 100 will not be displayed on the meter because it happens so fast.)
As the glass continues up into the slot of the Tint Meter, it crosses the path of the light beam. Consequently, the light being emitted by the L.E.D. on the photodiode has been diminished because the glass sample is blocking some of the light. Because the light has diminished, the photodiode produces less electrical current than before the glass crossed the path. The amount of current being produced by the photodiode with the glass in position, is compared to the amount produced before the glass was fully inserted. This comparison results in a percentage on the display of the Tint Meter expressing the light transmission of the glass sample.
In conclusion, the electrical current the photodiode produces has a direct relationship with the amount of light transmitted through the glass. This process is no different than shining a small flashlight onto the wall and seeing all the light being emitted by that flashlight as a bright circle. Now if you place sunglasses in front of the flashlight, and you will see the circle has gotten dimmer. The only difference with the Tint Meter is that electrical currents are used to measure the intensity of that beam before and after the sunglasses are put in front of that flashlight.
Interpreting Tint Meter Model 100™ Readings
The reading on a Tint Meter display denotes the amount of light passing through the glass. For instance, a reading of “35” infers a total visible light transmission of 35 %. If the state you are in has a light transmission requirement of not less than 35% total visible light transmission, then that means that any reading below 35% would fail the compliance requirement. When testing the meter’s calibration with the reference sample it is important to note the accuracy variation. The Model 100 Tint Meter™ has an accuracy of + or – 2%. If you were testing the meter with a sample that was labeled as 25%, a meter reading between 23% and 27% would indicate that the meter is properly calibrated. Any reading outside of that range would demonstrate that something is wrong with meter. The operator should check the cleanliness of the reference sample and inspect it for scratches. If the sample is OK then the battery should be changed and the meter retested. If this does not remedy the situation, contact Laser Labs for service.
Total Visible Light Transmission
Otherwise known as the VLT, is the net transmission of visible light passing through the glass. Visible light is a characterization of the light most seen by the human eye.
figure 6: Tint Meter Model 200™ photo
The Tint Meter Model 200™ is a hand held device manufactured by Laser Labs, Inc. of Scituate, Massachusetts that measures the amount of light that passes through a window. It measures the total amount of Visual Light Transmission (henceforth referred to as VLT) through a window and any coatings (tint film) on that window. The device was designed, as an affordable way for law enforcement officers to measure the total VLT of a window after it has been treated with aftermarket window film. The Model 200™ differs from the Model 100™ in several different ways. The first and most important is that it has the capability of measuring every window on an automobile, not just the side roll down windows. It can measure windows up to ½ inch thick. Second, it utilizes a two-piece design. Third, it requires a different method of calibration. Finally, it does not have an auto on-off switch, so care should be taken to shut both parts of the unit after use to prevent battery drainage.
Physical Characteristics
The Tint Meter Model 200™ is housed in two separate plastic enclosures. Each enclosure is 5.25 inches tall, 3.5 inches wide, and 1.5 inches deep. On the front of “Box A”, the unit that does the electronic processing, is a label noting the manufacturer, the model number, performance specifications and some simple directions. There is a clear window on the label to view the LCD readout. The second unit, “Box B”, that houses the light source has five exposed light emitting diodes (L.E.D.). The center L.E.D. is used for the Tint Meter’s light source for measuring light transmission, and the surrounding four L.E.D.’s are used for visually aligning the two units together. Also on Box B are two suction cups for attaching the light box (Box B) to the inside of rear windows that may be difficult to test with one operator.
Operating Instructions Tint Meter Model 200
How to perform a test
The Model 200 has a specific sequence that must be followed in order to calibrate the unit.
1. Turn on the light box (Box B).
Note: All five L.E.D.’s will be illuminated.
2. Place the meter box (Box A) on top of the light box (box B) in a cross hair pattern as shown in figures 7 and 8.
Note: There are two yellow squares on each side of Box A which should line up to the green L.E.D.’s on Box B.
figure 7: side view of alignment figure 8: top view of alignment
3. Turn on the meter box (Box A).
Note: Do not place reference plates between the two halves of the meter before turning the power on to Box A.
4. The meter is now calibrated to 100% light transmission.
Note: readings between 97% - 103% are acceptable.
5. Separate the 2 halves and place a reference sample on top of Box B.
6. Re-position Box A on top of Box B, and press the two halves firmly together.
7. The LCD read-out will register the total visible light transmission of that sample.
Note: The reference sample has a stated light transmittance value denoted on the label, and the readout should be within plus or minus 3 points of that stated value.
8. Remove the reference sample, and re-position the two halves together. The meter should register 100.
Note: If the reading has drifted(changed), turn Box A off, and back on again it should come back to 100% calibration.
9. Place Box B on the inside of the window being tested(see figure 9) by pressing the box firmly against the window until the suction cups have made a seal with the window. If you are testing the side roll down windows or the front windshield you do not have to affix the light box to the window if you feel comfortable holding both halves of the meter. Usually only the rear windshield requires using the suction cups.
Note: Make sure that both sides of the window area you are testing are clean and free of scratches. These obstructions can adversely affect the meter reading.
figure 9: Model 200 light box(box b)
affixed to the inside of a side window
10. Place Box A firmly on the opposite side of the window in the same cross hair pattern utilizing the yellow squares so they line up to the four green L.E.D.’s.(see figure 10)
Note: Box A must both be firmly placed against the window for most accurate readings.
figure 10: Model 200™ box A
properly aligned with box B on car
in the standard setup.
11. Once Box A is in proper alignment with Box B the meter will register the light transmission percentage on the LCD.
12. Remove Box A and Box B from the window, and re-position the two halves together to ensure 100 percent calibration.
13. Remember to turn both halves of the unit off before storage.
The Model 200 Tint Meter™ Theory of Operation
When a Tint Meter Model 200™ is positioned on a window it measures how much light is able to penetrate the surface of that glass and pass through to the other side. It does this by electrically measuring the brightness of light being emitted. Box B contains that light source. The L.E.D. positioned in the center of that box is regulated to emit a constant brightness. Box A contains the photocell to measure the brightness. Photocells work by generating electrical currents when they become in contact with a light source. When Box A and Box B are put into position to be calibrated there is nothing in between the two boxes to interfere with the light source, so when Box B is turned on it shines its constant light source on to the photocell housed in Box A. Because the light source is constant, which means it stays the same brightness, Box A is able to store that current and use it as a reference point for comparing the brightness of the L.E.D. when a glass sample is put in front of the light source. The Model 200™ registers and stores this electrical current in sample and hold circuit in a hundredth of a second(literally the second Box A is turned on). The reading Box A will displayed will be 100, inferring 100% light transmission, and if nothing is placed in front of the light source the reading will stay at 100 because the meter is comparing the electrical current it generated when Box A first turned to what it is generating with nothing in between the two boxes. Since there is nothing in front of the light source to change the brightness, there is no change to the electrical current being produced, and therefore it is registering 100% of the light source.
The next step is to separate the two halves in order to insert a glass sample for measurement. While the units are separated, Box A’s readings will be fluctuating up and down, and will not become stable again until it is placed back in alignment with Box B. This is because the meter is constantly taking measurements of the light that is shining on the photocell. For instance room light, and sun light. Since these light sources are generally brighter than the L.E.D. in Box B, the numbers on the readout are usually higher than 100%. If Box A’s is placed flat against the table so no light can shine on the cell the reading should be zero. The reason it is zero is because the meter is comparing how much light is shining on the photocell, none, to when the two halves were calibrated together. So reading should be zero light transmission, which the Model 200™ does display. Now that the two halves are separated, a glass sample can be placed in between the two units. When Box A is repositioned over Box B with the glass sample in place, the reading will register the amount of light able to pass through the glass. Repositioning is very important to accurate meter readings and that is why there are 4 L.E.D.’s surrounding the foam gaskets on Box B. If you look at the the photocell on Box A it is approximately ¾ of an inch in diameter. When Box A is placed directly over Box B the L.E.D. shines directly in the center of that photocell, and the photocell is able to capture all of the light being emitted by that L.E.D. For example, calibrate Box A to Box B. The meter will read 100, now slide Box A off center just a ¼ of an inch, and the readings will go down. That is because the photocell is not capturing all the light being emitted by the L.E.D. Some of the light is shining on the foam gasket of Box A and not on the photocell. If you continued to slide Box A so that it was an inch off center the reading would be zero. Similar situation to placing the meter against the table, no light is shining on the photocell, and the meter is registering zero light transmission. That is why alignment is critical to accurate readings. The two ways to know you have perfect alignment is first by lining up the yellow alignment squares on Box A to the L.E.D.’s on Box B, and when measuring a window to find the highest reading the meter will display. Because if your off center by that ¼ of an inch the numbers will go down, as in lower light transmission, rather go up. Eventually if Box A was so far off center that the photocell started picking up other light sources such as sun light passing through the window, the reading would start to rise, and if it were a clear window you were testing, the readings would probably pass 100%. Which, is because the ambient light is brighter than the L.E.D.
The Foam gaskets on both units are critical components of Model 200™ for obtaining accurate light transmission readings. As mentioned earlier ambient light such as room light, and sun light are generally brighter than the light source emitted by the L.E.D. in Box B, and therefore cause the readings to be inflated. When the two halves are in position to be calibrated to 100% with the Tint Meters™ light source(the L.E.D. in Box B), the foam gaskets are placed tightly, and squarely on top of each so that no light other than the light from the L.E.D. can shine on the photocell. This allows for perfect comparisons of the amount of light being emitted before a glass sample is tested and during a glass sample is being tested. That is because ambient light can not be guaranteed to be constant. For example, your outside, it’s a sunny day, the light appears to be constant, but then a cloud passes. What happens is it gets slightly darker or when you turn away from the sun and you see your shadow on the ground. If you measured the amount light on your shadow to the amount next to your shadow it would be different. That is why the foam gaskets are critical to accurate readings, and the two halves, Box A and Box B should pressed as firmly as possible against a window when performing a test.
Interpreting Tint Meter Readings
The reading on a Tint Meter display denotes the amount of light passing through the glass. For instance, a reading of “35” infers a total visible light transmission of 35 %. If the state you are in has a light transmission requirement of not less than 35% total visible light transmission, then that means that any reading below 35% would fail the compliance requirement. This is due to the accuracy of the meter. The Model 200 Tint Meter™ has an accuracy of + or – 3%. When testing the meter’s calibration with the reference sample it is important to note the accuracy variation. If you were testing the meter with a sample that was labeled as 25%, a meter reading between 22% and 28% would indicate that the meter is properly calibrated. Any reading outside of that range would demonstrate that something is wrong with meter. The operator should check the cleanliness of the reference sample and inspect it for scratches. If the sample is OK then the batteries should be changed and the meter retested. If this does not remedy the situation, contact Laser Labs for service.
Total Visible Light Transmission
Otherwise known as the VLT, is the net transmission of visible light passing through the glass. Visible light is a characterization of the light most seen by the human eye.
Each Tint Meter has two light transmittance reference samples to verify its accuracy. These samples are the same for both models. A reference sample is a 3 inch by 4 inch section of translucent material, one eighth of an inch thick. On the translucent material is a label stating the light transmittance value. The value is the total amount of light able to pass through the material. This value is determined by a spectrophotometer, which is the industry standard for measuring light transmissions. There are two reference samples with a Tint meter for a specific purpose. One reference sample has a high light transmittance value, and the other has a low light transmittance value. The reason for this is so the meter can be tested for accuracy at more than one spot from zero to one hundred percent. Many of the states’ sun-screening laws vary from a low of 6% to a high of 70%. If you only have one sample to verify the meter’s accuracy, and the it has a stated value of 70% light transmission, and you are testing a window for compliance at a 35% light transmission, you cannot verify the accuracy of that meter at 35%. With two reference samples, a larger range of verifiable accuracy is achieved. To bring this range of accuracy one step further, a 1/8th inch piece of cardboard can be used to test the Tint Meter™ at zero percent(0%) light transmission. Sliding the cardboard into the slot like a reference sample should achieve a reading of 0%. If the Model 100 Tint Meter™ is activated without placing a sample all the way into the slot, the meter should read 100% light transmission. The Model 200 Tint Meter™ can be tested at 0% transmission by first calibrating it as outlined in the Model 200 operation section and then turning off the light box (box B) without removing the meter (box A) from box B. The reading on the screen should drop to 0%. In order to test the model 200 with reference samples calibrate it as described in section II B. Then place the reference sample between the two halves of the meter. This is just the same as placing a window between them. Be careful not to block the center LED with the label on the reference sample. In short, you can test a Laser Labs, Inc. Tint Meter at four separate transmission percentages to verify the accuracy.
Tint meters should be tested for accuracy every time the meter is used.
Reference samples supplied by Laser Labs, Inc. are noted as being traceable to N.I.S.T. traceable standards. N.I.S.T. is an acronym for the National Institute of Standards and Technology, is a non-regulatory federal agency within the Commerce Departments Technology Administration. NIST's mission is to promote economic growth by working with industry to develop and apply technology, measurements, and standards.
Window film is applied to motor vehicle windows to reduce sun glare, block out harmful ultra violet rays, and for privacy. The federal government has a motor vehicle safety code that pertains to the tinting of automotive glass that must be adhered to by the individual automotive manufacturers. This code however is different than the laws promulgated by individual states with regard to after market window films. In a majority of the states, window film may be applied to some or all of an automobiles side and rear windows. No film is allowed on the windshield below the AS1 line in any state. Each state has the authority to enact rules and regulations regarding the darkness of those films applied. How they regulate darkness is by using a similar standard of measuring the light transmission. Thirty five percent light transmission is a common value used by the regulatory authorities. What this thirty five percent means is that the light transmission of the window must have at least thirty five percent light passing through the glass. So if a window has less than 35 percent light transmission it fails the requirements.
Since the inception of window tint meter, many of the states have had to revise their window tinting statues. Prior to an electronic means of measuring window film applied to windows, certain films would be approved for use to be applied to windows. A Regulatory agency may have stated that a 35 percent window film could be installed on car windows. This method became unenforceable as the meters became available, since there would be no way to measure the light transmittance of the window film after it has been installed, with out having to tear the film off. Now the term used is the “Net Light Transmittance” of the window. The “Net” being the combined light transmittance of the film and the window.
Windows do not have a 100 percent light transmission. A clear pane of glass has a physical standard of 92 percent light transmission. Automotive glass has safety glazing installed to protect the occupants. The glazing material may bring this light transmittance value down to a minimum of 70 percent light transmission, as permitted by federal regulatory agencies. Now if you add a window film that has a 50 percent light transmission over a window having a 70 percent light transmission it brings the “Net” light transmission down to 35 percent light transmission (.70 x .50 = .35).
Some window films being installed have a high reflectivity. Reflectivity is measured differently than light transmittance. It is possible to have reflective films applied to windows that pass the light transmittance requirements, yet block out the occupants from field of view. Tint Meters do measure the light transmittance value accurately of reflective window films. The higher the reflectivity, the lower the light transmittance value.
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