Description
A luxmeter is a device that measures illuminance and luminous emittance using the SI unit of lux. It effectively measures the amount of power from the light falling on a given unit of area, except that the power measurement is weighted to reflect the sensitivity of the human eye to varying wavelengths of light. A lux meter measures how bright the light falling on the sensor is. The aim of this work is to build a luxmeter using Arduino, an LCD shield, the LDR, and a 5 kohm resistor.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE PROJECT
- PROBLEM STATEMENT
- AIM AND OBJECTIVE OF THE PROJECT
- PURPOSE OF THE PROJECT
- SCOPE OF THE PROJECT
- LIMITATION OF THE PROJECT
- APPLICATION OF THE PROJECT
- RESEARCH QUESTION
- METHODOLOGY
- PROJECT ORGANISATION
CHAPTER TWO
LITERATURE REVIEW
- REVIEW OF MEASURING LIGHT INTENSITY USING A LUX METER
- REVIEW OF THE RELATED STUDY
- OVERVIEW OF LUX
CHAPTER THREE
3.0 METHODOLOGY
3.1 BLOCK DIAGRAM OF THE SYSTEM
3.2 SYSTEM WORKING PRINCIPLE
3.3 HARDWARE REQUIRED
3.4 LUX METER BUILDING
3.6 SYSTEM CODE
3.7 IMPLEMENTATION
CHAPTER FOUR
4.0 TESTING AND RESULTS
- CONSTRUCTION PROCEDURE AND TESTING
- INSTALLATION OF THE COMPLET DESIGN
- ASSEMBLING OF SECTIONS
- TESTING OF SYSTEM OPERATION
- RESULT
CHAPTER FIVE
- CONCLUSION
- RECOMMENDATION
- REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Accurate and quantifiable measurement of light is essential in creating desired outcomes in practical day to day applications as well as unique applications. From measuring the amount of light in a work space surface, to ensuring emergency exits have proper illumination, light measurement and analysis is an important step in ensuring efficiency and safety. To perform these measurements, technicians often make use of lux meters which are specialized devices that measure the intensity of light falling on a surface, or “lux.”[1] [8]
Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit. The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square meter. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit, watts per square meter, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, “lux” is used in both singular and plural.
The light sensor for a lux meter can be one of several different types of sensors, including photodiodes and phototransistors, but the easiest to use and often the most readily available type of sensor is a photoresistor or light dependent resistor (LDR). As you would expect, the resistance of an LDR changes as the amount of light falling on it changes. If you can measure the resistance of the LDR and you know the characteristics of your particular LDR, you can quantify the amount of lux falling on the LDR. In general, the brighter the light, the lower the resistance, but unfortunately, the relationship between resistance and lux for an LDR is not a nice linear relationship. It is instead an exponential relationship which is a little trickier to deal with. With a little bit of time though, you can take a few measurements to determine the mathematical relationship between resistance and lux and program the relationship into a microcontroller to create a simple and reasonably effective lux meter.
1.2 PROBLEM STATEMENT
It is very difficult to determine the amount of light in a particular environment with our physical eyes, in order to solve this problem a lux meter was build. A luxmeter is a device measures illuminance and luminous emittance using the SI unit of lux. It effectively measures the amount of power from the light falling on a given unit of area, except that the power measurement is weighted to reflect the sensitivity of the human eye to varying wavelengths of light. A simpler way to describe a lux meter is to say that it measures how bright the light falling on the sensor is.
1.3 AIM AND OBJECTIVE OF THE PROJECT
The main aim of this work is to build a device that measures illuminance and luminous emittance using the SI unit of lux. At the end of this work, student involved shall be able to achieve the following:
- process of characterizing an LDR,
- writing software that can calculate illuminance and
- then building an LDR and Arduino based luxmeter.
1.4 PURPOSE OF THE PROJECT
The purpose of this work is to effectively measures the amount of power from the light falling on a given unit of area
1.5 APPLICATION OF THE PROJECT
Lux meter is used to measure the intensity of light. These precise measuring tools have been carefully engineered using state of the art technology and find usage in multiple applications, such as in Photographic Mesurements : It also measures the photography subject’s illuminance. Also In photometry, this is used as a measure of the intensity, as perceived by the human eye. We use it in our labs to measure visibility and maintains it by providing extra bulbs/tubes, so that we can provide good visibility to complete day to day tasks with comfort.
Lux meter also used to measure levels of light in schools, hospitals, production areas, laboratories
1.6 SCOPE OF THE PROJECT
The amount of light is an important issue in several scenarios ranging from scenic design, light pollution study, robots navigation, occupational health and safety, illumination engineering, agriculture, medical appliances and many more. It is typically determined by using an illumination meter. The meter, also known as lux meter is used to measure the density of light in an area which measured in lx unit. It is used in photometry as a measure of the intensity, as perceived by the human eye of light that hits or passes through a surface. As in normal meter, the lux value was obviously a displayed value, and hardly used for embedded application as well as for lighting monitoring considering its expensive price. This limits the lighting monitoring in certain critical field. Therefore, in this paper, we present our initial works on the development of a webcam based lux meter that is applicable and suitable for lighting monitoring as well as the ability to be used in embedded application.
1.7 LIMITATION OF THE PROJECT
- The LDR luxmeter is not incredibly accurate, but can be good enough in some conditions.
- During LDR characterization, it is very important to ensure the light falling on the LDR and commercial sensor is identical.
- The LDR luxmeter is cheap and easy to make. You only need one commercial light sensor to help you make as many LDR light sensors as you want.
1.8 RESEARCH QUESTION
- How does LDR measure light intensity?
- Which type of resistor is used for measuring the intensity of light?
- What is the output of LDR Sensor?
- How does an LDR work? What is the use of a lux meter?
- What are the principles of a lux meter?
- What is a lux meter?
- How does a lux meter work?
- What is lux meter and how does it operate?
1.9 METHODOLOGY
To achieve the aim and objectives of this work, the following are the steps involved:
- Study of the previous work on the project so as to improve it efficiency.
- Draw a block diagram.
- Test for continuity of components and devices,
- Design of the device was carried out.
- Studying of various component used in circuit.
- Construction of the circuit was carried out. The construction of this project includes the placing of components on Vero boards, soldering and connection of components,
- Finally, the whole device was cased and final test was carried out.
1.10 PROJECT ORGANISATION
The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 REVIEW OF MEASURING LIGHT INTENSITY USING A LUX METER
Accurate and quantifiable measurement of light is essential in creating desired outcomes in practical day to day applications as well as unique applications. From measuring the amount of light in a work space surface to ensuring emergency exits have proper illumination, light measurement and analysis is an important step in ensuring efficiency and safety. To perform these measurements, technicians often make use of lux meters which are specialized devices that measure the intensity of light falling on a surface, or “lux.”
Examples of practical uses of lux meters include: Checking for lighting system adequacy in office spaces. Natural lighting alone is inadequate to properly illuminate most work and office spaces. Not everyone has a corner office which affords them a sea of natural light. Most offices and buildings supplement daylight with synthetic lighting during working hours. Increasing the level of illumination enable people to work safely and efficiently. Light meters are used to ensure that the light levels fall within a certain level where it is bright enough but not too bright to cause glare. In fact, lux meters can be used to help enhance productivity, because having the correct level of lighting means that workers experience less fatigue and consequently, higher efficiency.
Enhancing the visibility and utility in outdoor spaces. Streets and parking lots, must be well lit at night. Unfortunately, it can be difficult to ensure that lighting systems perform adequately during nighttime conditions without producing too much light, which can be distracting to motorists and can waste money on energy bills. Using lux meters, though, street lighting and parking lot designers can test the performance of their lighting systems and adjust them to produce the best amount of light, and not hamper the night vision of motorists and pedestrians.
Optimizing light levels in museums and art galleries. Artwork and paintings are often exhibited to a large number of people and lighting can make or break the exhibit. If the light levels are too low then details can be missed by viewers. On the other hand, having too much light will wash out the colors and the artwork may not have the same impact intended by the artist. Museum lighting designers rely on light meters to help them set the correct levels of lighting in order to properly exhibit precious works of art.
2.2 REVIEW OF THE STUDY
Malaysia has been surprised by the collapse of Stadium Sultan Mizan Zainal Abidin, Terengganu on June 2009 [1]. It took a year to repair the stadium, and after its completion, the country once again surprised by the stadium’s spotlight that was claimed not following the specification for AFC Cup 2012, despite the millions of costing involved [2]. Literature [3] has conduct a study on illumination problem in elderly nursing homes and their result has shown that there are insufficient lighting to meet the visual needs of older people. There are also studies conducted in the USA on the lighting assessment and their effects in security issues [4][5]. These scenarios explained the importance of lighting monitoring and assessment in our daily routines. The lighting issues were not given serious attentions when people are designing something in their field.
The results of neglecting them could be sometimes devastating, both finance-wise and time-wise. This issue we believe, could be solved at its earliest stage i.e. design stage with a constant lighting monitoring every time.
A lux meter is a handheld device for measuring brightness. It specifically measures the intensity in which the brightness appears to the human eye. This is different than measurements of the actual light energy produced by or reflected from an object or light source. The lux is a unit of measurement of brightness, or more accurately, illuminance. It ultimately derives from the candela, the standard unit of measurement for the power of light. A candela is a fixed amount, roughly equivalent to the brightness of one candle. While the candela is a unit of energy, it has an equivalent unit known as the lumen, which measures the same light in terms of its perception by the human eye. One lumen is equivalent to the light produced in one direction from a light source rated at one candela. The lux takes into account the surface area over which this light is spread, which affects how bright it appears. One lux equals one lumen of light spread across a surface one square meter. A lux meter works by using a photo cell to capture light. The meter then converts this light to an electrical current. Measuring this current allows the device to calculate the lux value of the light it captured. Conventional lux meter device.
The most common use of a lux meter is in photography and video filming. By measuring the light in luxes, photographers can adjust their shutter speed and depth of field to get the best picture quality. The device can also be very useful for filming outdoor scenes of television programs or movies as it allows adjustments to make sure scenes filmed in different light levels have a consistent brightness on screen. Another common use of a lux meter is in meeting health and safety regulations [6]. It can be used to check whether the brightness of a room is enough to meet any rules designed to protect workers from suffering damage to their eyesight. Using a lux meter takes into account the size of the room in a way that simply measuring the intensity of the light source in lumens would not.
2.3 OVERVIEW OF LUX
The lux is the SI derived unit of illuminance, measuring luminous flux per unit area.( Schlyter, 1997-2009). It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, “lux” is used as both the singular and plural form.[ Christopher C, 2017]
Luminance
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total “amount” of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area when the luminous flux is held constant.
One lux is equal to one lumen per square metre:
1 lx = 1 lm/m2 = 1 cd·sr/m2.
A flux of 1000 lumens, concentrated into an area of 1 square metre, lights up that square metre with an illuminance of 1000 lux. However, the same 1000 lumens, spread out over 10 square metres, produces a dimmer illuminance of only 100 lux.
Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.
The illuminance provided by a light source on a surface perpendicular to the direction to the source is a measure of the strength of that source as perceived from that location. For instance, a star of apparent magnitude 0 provides 2.08 microlux (μlx) at the Earth’s surface.[15] A barely perceptible magnitude 6 star provides 8 nanolux (nlx).[16] The unobscured Sun provides an illumination of up to 100 kilolux (klx) on the Earth’s surface, the exact value depending on time of year and atmospheric conditions. This direct normal illuminance is related to the solar illuminance constant Esc, equal to 128000 lux (see Sunlight and Solar constant).
The illuminance on a surface depends on how the surface is tilted with respect to the source. For example, a pocket flashlight aimed at a wall will produce a given level of illumination if aimed perpendicular to the wall, but if the flashlight is aimed at increasing angles to the perpendicular (maintaining the same distance), the illuminated spot becomes larger and so is less highly illuminated. When a surface is tilted at an angle to a source, the illumination provided on the surface is reduced because the tilted surface subtends a smaller solid angle from the source, and therefore it receives less light. For a point source, the illumination on the tilted surface is reduced by a factor equal to the cosine of the angle between a ray coming from the source and the normal to the surface.[17] In practical lighting problems, given information on the way light is emitted from each source and the distance and geometry of the lighted area, a numerical calculation can be made of the illumination on a surface by adding the contributions of every point on every light source.
Relationship between illuminance and irradiance
Like all photometric units, the lux has a corresponding “radiometric” unit. The difference between any photometric unit and its corresponding radiometric unit is that radiometric units are based on physical power, with all wavelengths being weighted equally, while photometric units take into account the fact that the human eye’s image-forming visual system is more sensitive to some wavelengths than others, and accordingly every wavelength is given a different weight. The weighting factor is known as the luminosity function.
The lux is one lumen per square metre (lm/m2), and the corresponding radiometric unit, which measures irradiance, is the watt per square metre (W/m2). There is no single conversion factor between lux and W/m2; there is a different conversion factor for every wavelength, and it is not possible to make a conversion unless one knows the spectral composition of the light.
The peak of the luminosity function is at 555 nm (green); the eye’s image-forming visual system is more sensitive to light of this wavelength than any other. For monochromatic light of this wavelength, the amount of illuminance for a given amount of irradiance is maximum: 683.002 lux per 1 W/m2; the irradiance needed to make 1 lux at this wavelength is about 1.464 mW/m2. Other wavelengths of visible light produce fewer lux per watt-per-meter-squared. The luminosity function falls to zero for wavelengths outside the visible spectrum.
For a light source with mixed wavelengths, the number of lumens per watt can be calculated by means of the luminosity function. In order to appear reasonably “white”, a light source cannot consist solely of the green light to which the eye’s image-forming visual photoreceptors are most sensitive, but must include a generous mixture of red and blue wavelengths, to which they are much less sensitive.
This means that white (or whitish) light sources produce far fewer lumens per watt than the theoretical maximum of 683.002 lm/W. The ratio between the actual number of lumens per watt and the theoretical maximum is expressed as a percentage known as the luminous efficiency. For example, a typical incandescent light bulb has a luminous efficiency of only about 2%.
In reality, individual eyes vary slightly in their luminosity functions. However, photometric units are precisely defined and precisely measurable. They are based on an agreed-upon standard luminosity function based on measurements of the spectral characteristics of image-forming visual photoreception in many individual human eyes.
CHAPTER THREE
3.0 METHODOLOGY
3.1 SYSTEM BLOCK DIAGRAM
Before carrying out any project, the block diagram must be drawn and fully understood. Block diagram gives a pictorial understanding of any work. The block diagram of the system is as below:
3.2 SYSTEM WORKING PRINCIPLE
Most of the lux meters consist of a body, photocell or light sensor, and display. The light that falls on to the photocell or sensor contains energy that is converted to electric current. In turn, the amount of current depends on the light that strokes the photocell or light sensor. Lux meters read the electrical current, calculate the appropriate value, and shows this value on its display.
3.3 HARDWARE REQUIRED
- 1 light dependent resistor (it doesn’t matter which one, you don’t even need to know the part number)
- 5 kilo ohm resistor
- Arduino
- 2×16 LCD shield
- Breadboard
- Digital Multimeter (DMM)
- Commercial lux meter (for characterizing your LDR)
3.4 LUX METER BUILDING
Building the lux meter is very simple. Components needed are Arduino, an LCD shield, the LDR that I just characterized and a 5 kohm resistor. In theory, you could use any resistance value, but I chose 5 kohm because the resistance of the LDR was in the order of a few kilo-ohms under typical room lighting conditions. I plugged the shield into the Arduino, and then built a simple voltage divider circuit with the LDR and resistor. This voltage divider circuit is the crux of the sensor circuit. The 5 volt supply is split between the LDR and the 5 kohm resistor. As the resistance of the LDR changes, the fraction of the voltage across the two resistors also changes. If the voltage across the 5 kohm resistor is measured using the Arduino, it is very easy to add some code that will determine what resistance the LDR is exhibiting. The LDR is connected to 5V, the resistor is connected to ground, and the point in between is connected to analog input 0.
This voltage divider circuit can be connected directly to the LCD shield and doesn’t need a breadboard. This picture shows the completed circuit with the LDR and 5 kohm resistor in the LCD shield.
3.5 SYSTEM CODE
The equation obtained in Part 1 relates the illuminance to the resistance, but the analog input pin of the Arduino only measures voltage, so there are a couple of calculations that have to be done to obtain the resistance.
First the digital representation of the analog voltage must be obtained by using the analogRead function (remember that this is the voltage across the 5 kohm resistor, not the voltage across the LDR)
rawData = analogRead(LDR_PIN);
Second, the digital representation must be converted back into a voltage by scaling the analog-to-digital converter value to the reference voltage:
// MAX_ADC_READING is 1023 and ADC_REF_VOLTAGE is 5
resistorVoltage = (float)ldrRawData / MAX_ADC_READING * ADC_REF_VOLTAGE;
Third, the LDR voltage must be determined. Since 5V is split between the 5 kohm resistor and the LDR, simply subtract the resistor voltage from 5V:
ldrVoltage = ADC_REF_VOLTAGE – resistorVoltage;
Finally, the resistance of the LDR must be calculated based on the voltage (simple resistance calculation for a voltage divider circuit):
ldrResistance = ldrVoltage/resistorVoltage * REF_RESISTANCE; // REF_RESISTANCE is 5 kohm
Once the resistance is obtained, the illuminance (in lux) can be calculated and the value can be output to the LCD.
ldrLux = LUX_CALC_SCALAR * pow(ldrResistance, LUX_CALC_EXPONENT);
// LUX_CALC_SCALAR and LUX_CALC_EXPONENT are determined by the Excel spreadsheet
// They are set to 12518931 and -1.405 respectively in my example
The calculations and display output are all done in the loop function and the entire source code for the sketch can be found below. An LCD shield from Adafruit is used to display the lux measurement, so their LCD library must be downloaded for this sketch to work
3.6 IMPLEMENTATION
The hardware has been assembled, the code has been written, all that needs to be done is upload the code and compare the results to the commercial light meter. In the video below you can see a side by side comparison of the LDR light meter and an LX-102 light meter from Lutron. At standard room light levels (500 lux and below), the two light meters were within 40 or 50 lux of each other. Under brighter lights, the difference grew to 100 lux or more. This is likely because the characteristic curve I determined experimentally deviates from the actual characteristic curve. If I took more samples and especially focused on getting samples in the range of lighting conditions that I expect to measure, I would probably end up with an equation that more closely represents the actual characteristic curve.
Overall, I would say that the LDR light meter is good enough in a normal room when you just want a ballpark measurement of the lighting levels, but if you want precise and accurate measurements you will need to use a different kind of sensor.
CHAPTER FOUR
4.0 TEST AND RESULT ANALYSIS
- CONSTRUCTION PROCEDURE
In building this project, the following procedures were properly considered, Purposing of the entire materials / Components needed
- Resistance check of the components bought with the help of ohmmeter before making the necessary connection with the components
iii. Drafting out a schematic diagram or how to arrange the materials / components.
- Testing the completed system to see if the design works and
- Finally, implementation of design of the project.
Having procured all the materials, I processed into the arrangement of the components into the Vero board but we could not laid the I.C directly on the bread board because the heat soldering iron emits while soldering, proper soldering of the components then followed. The components were all soldered into the board after which it was correctly confirmed done.
4.2 CASING AND PACKAGING
All the components were soldered onto the Vero Board. Then after that, a case was gotten where the entire circuit was mounted follow by other external components such as sensor, and meter.
4.3 ASSEMBLING OF SECTIONS
Having provided the casing and having finished the construction of the sections of this system, the assembling into the casing followed. The sections were properly laid out and assembled into the casing where the general coupling and linkages into the peripheral devices took place.
Finally; the indicator was brought out to indicate when the system is powered. Switch was brought out for powering the system, sensor and meter was also brought out of the casing
4.4 PACKAGING
This is a very important aspect of the design work. It is the appearance given to the final work. After soldering on the vero board, we do not leave the work like that; it has to be cased. Packaging could serve two major functions.
- Serve to protect the components used for the design.
- Serve to make the finished work look attractive.
A portable plastic casing covered with leather was used in packaging the work. The dimension and design of the box was arrived at after considering various factors such as the width and length of the vero board
The dimension for the casing is:
Length — 31.5 cm and 26.5cm
Height — 14.cm
The vero board and other devices are held firmly by bolts and nuts.
4.5 MOUNTING PROCEDURE
The entire circuit was bolted directly to the bottom of the case. This was followed by mounting of the power section which is the 9v battery. A gap was made between one mounting and the successive ones. This is necessary to avoid over-crowding. The veroboard is also mounted at the upper side of the case. The resistors, phototransistor, and other components used were mounted on the vero board. All the accessories were highly fixed to avoid slack that may result in the process of operations
4.6 TESTING
Testing is one of the important stages in the development of any new product or repair of existing ones. Because it is very difficult to trace a fault in a finished work, especially when the work to be tested is too complex. For the purpose of this project, two stages of testing are involved.
i. Pre-implementation testing
- Post-implementation testing.
4.1.1 PRE-IMPLEMENTATION TESTING
It is carried out on the components before they are soldered to the veroboard. This is to ensure that each component is in good working condition before they are finally soldered to the board.
The discrete components are tested with a millimeter by switching the meter to the required value and range corresponding to each discrete component to check for continuity.
4.1.2 POST-IMPLEMENTATION TESTING
After implementing the circuit on a project board, the different sections of the complete system were tested to ensure that they were in good operating condition. The continuity test carried out is to ensure that the circuit or components are properly linked together. This test was carried out before power was supplied to the circuit. Finally, after troubleshooting has been done on the whole circuit, power was supplied to the circuit. Visual troubleshooting was also carried out at this stage to ensure that the components do not burn out.
The circuit was tested in the day time, for that reason, a dark object was allow to pass through the sensor (phototransistor) and the meter was seen deflecting.
4.7 RESULT
The results obtained during the construction states after necessary troubleshooting were satisfactory. The system was able to respond to its operation.
CHAPTER FIVE
5.1 CONCLUSION
At the end of this work the main aims of this work was achieved which is to build a portable lux meter. The result shows a very convincing result where the image features has potential correlation to the actual lux meter.
This lux meter has also satisfy our early requirements which are to be able to be use in an embedded applications compared to the conventional lux meter where tapping the value from the portable device is merely impossible. In future, the lighting mathematical model is being formulated and we predict that the lux value based on this mathematical model will be more accurate, and more useful in manipulating the lux values.
5.2 RECOMMENDATION
Working on this topic as my project is a good idea and it comes at the right time. I am suggesting that this particular topic should also be given to other students both in higher and lower class.
Selecting lux meters or light meters requires certain performance specifications include photocell, illumination range, Lux resolution, operating temperature and foot candle resolution. Special features include low battery Indicators, low voltage, alarms, remote light sensors, built-in memory, auto power off, zero function etc.
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