5 Fundamental Parameters of an Imaging System

The following parameters are the most basic concepts of imaging and are important to understand when studying more advanced topics:

  1. Field of View (FOV): The viewable area of the object under inspection. This is the portion of the object that fills the camera’s sensor.
  2. Working Distance (WD): The distance from the front of the lens to the object under inspection.
  3. Resolution: The minimum feature size of the object that can be distinguished by the imaging system. Learn more in Resolution.
  4. Depth of Field (DOF): The maximum object depth that can be maintained entirely in acceptable focus. DOF is also the amount of object movement (in and out of best focus) allowable while maintaining focus. Learn more in Depth of Field and Depth of Focus.
  5. Sensor Size: The size of a camera sensor’s active area, typically specified in the horizontal dimension. This parameter is important in determining the proper lens magnification required to obtain a desired field of view.
  6. PMAG: The Primary Magnification of the lens is defined as the ratio between the sensor size and the FOV. Although sensor size and field of view are fundamental parameters, it is important to realize that PMAG is not.

                PMAG = Sensor size(mm)/field of view(mm) (1)

Note: Typically, only horizontal values are used.

Diagram of Fixed Focal Lenses

Fig1: Diagram of Fixed Focal Lenses

Article is posted by Optics For Hire – lens manufacturing Consultant.

The Fundamental Aspects of a Light Guide Panel

A light guide panel (LGP) is an acrylic light guide panel made from pure Poly (methyl methacrylate) (PMMA) resin. It has two main sections:

  1. The bottom section where either a dot matrix is printed or a line matrix is scratched.
  2. The edges where the light source is installed.

At any given instance,when light source is directed towards the light guide panel,the light is distributed evenly over the upper surface of the panel. It was mainly designed to optimize the uniformity of light distribution,which makes the backlight slim and as a result,reorients the line or dot light source (e.g. from LED or fluorescent lamp) to the plate light source. There are a number of LGP which have been designed to be used for in-store decorations,lighting equipment etc. In situations where they have been designed to use LED as the main source of energy,they can reduce the power consumption significantly.

The light guide panels have quite a number of specifications which you need to consider when you are planning to purchase them for any application. In this case,the choice of material is never an element to consider since all LGP are manufactured from acrylic material however,they vary in both thickness and weight. For instance,the most common types of LGP have a thickness between 5mm and 8mm with the weight varying between 10kg and 22kg. This does not imply that these are the only sizes which are available in the market.Different companies design light guide panels of different sizes. You need to know the exact surface pattern of LGP you would wish to buy.

ABC

Broadly, there are two most common types of surface patterns which can be classified as:a one sided light emission with a back side dot pattern and a two-sided light emission with both faces with a dot pattern. Of course,there is a lot of scientific research going on in the LGP industry with an attempt to produce cost effective and efficient products. For instance,the introduction of slim LGP which had been designed to be used with LED sign boards did revolutionize this industry. Since then,most products which have so far been launched feature the edge-light system (ELS).

The ELS-LGP are commonly used in a number of indoor and outdoor applications. It is worth noting that these products are thinner and have the capability of illuminating a larger surface area. Moreover,they are cost effective since they have reduced the installation costs and the running costs. In fact,with the advancement of the LGP technology,sign boards which are as large as 1.5m by 2.3m can be illuminated conveniently.

To improve their effectiveness,they are also fitted with a reflective sheet. This basically implies that whenever light is emitted from the source,it travels through the panel in a controlled manner within the interior of the LGP. It is again radiated via the diffusion sheet which is part of the panel’s surface. The major advancements in this industry have been focusing mainly on the following key areas:

  1. The ability to make very thin sign boards using the available light guide panels. This can only be realized by not attaching luminous sources to panel’s edge.
  2. It eliminates the patchy appearance which is a common scenario with fluorescent sign boards by ensuring an even distribution of light.
  3. Introducing eco-friendly products by ensuring that small amount of energy is used in the entire process and reducing the carbon dioxide emissions. In addition to these,the recent development has also championed for the use of mercury free light sources.
  4. It has reduced costs significantly by replacing fluorescent light sources with LEDs which has a longer service life thereby reducing maintenance costs significantly.

Buyers can choose from the three combination of products which are available in the market which include:acrylic LGP which a diffusion sheet;acrylic LGP with both LED modules. It follows that,this technology is really essential in creating billboards,information boards,hanging signs, in-store menu signs etc. The main features which are associated with the light guide panels include:

  • They are energy efficient – The cost of energy has been increasing in the recent past thus,any process which can save significant amount of energy ought to be implemented. The use of LEDs as opposed to fluorescent lamps can reduce energy consumption by between 70% and 80%.This has been one of the main reasons why a number of companies have been adopting this technology.
  • Safety – The LEDs which are used in the LGP operate at about 2°C above the room temperature in most cases. This reduces the risks of fire.This is not the case for the fluorescent lamps which dissipate a lot of heat.
  • Reduced maintenance costs – LEDs have a longer life span that the ordinary fluorescent lamps.This reduces the maintenance costs significantly since the service life of LEDs is ten times more than the fluorescent lamps.

In addition to these,it is also important to note that LGP are transparent since they are constructed using acrylic thus,they can achieve a transmittance of about 92%. It is quite evident that this technology has quite a number of advantages more so when it is being used as a way to advertise products and services. This is due to its efficiency,reliability and cost effectiveness.

To enjoy all the benefits they are associated with,there is only one way to go about the entire process.

You need to get a professional and a reputable company which will take you through the entire design process and the implementation. Get the LGP products from Excelite since you will get a professional guidance about light guide panels. There are quite number of companies which claim to offer such products however,what makes Optics For Hire to standout is their commitment to ensure that all customers get quality products and essential resources they need.

The Five Building Blocks Of An Efficient, High-Brightness LED Driver (Part – II)

Five Building Blocks Of An Efficient LED Driver

HYSTERETIC CONTROLLER

The main function of the hysteretic controller is to regulate current through the LED. A reliable hysteretic controller may use an SR-type flip-flop where the “Set” input is triggered when the current falls below the lower threshold, and the “Reset” input is triggered when the current rises above the upper threshold. By using digital-to-analog converters (DACs) to produce the reference voltages, a hysteretic controller can be made programmable.

With resolution defined by the capability of the DACs, the higher and lower reference values can be controlled to change the position of the ripple current. Reducing the amount of ripple allowed in the channel decreases the ramp times, increasing the switching frequency. Drivers that can work at higher frequencies (ranging from 500 kHz to 2 MHz) can allow for significant reductions in the cost and size of magnetics. In addition, the controller must be able to perform a logical AND of signals from the modulator and trip circuitry.

CURRENT SENSE AMPLIFIER

A high-side sense amplifier allows the hysteretic controller to sense both the rising and falling current ramps of the inductor. Such a CSA needs to differentially sense the voltage and level shift it to the same reference voltage as the hysteretic controller. The CSA operates by creating a current ISENSE in the low-voltage realm that is proportional to VSENSE on the high side. An additional amplifier with adjustable gain can be used to obtain a signal whose voltage matches that obtained from the reference DACs in the hysteretic controller. A high gain setting in the CSA enables the use of low-value sense resistors, minimizing the power losses, and a choice between 20 and 100 should address the requirements of most HBLED designs. Since the CSA is sensing the rising and falling currents, it is important for the sensor’s bandwidth to be greater than the switching frequency. When high bandwidth is not required, choosing a lower one will reduce the noise picked from the supply through the positive pin of the differential amplifier.

GATE DRIVER AND FET

As the gate driver and FET are intrinsically tied to the maximum switching frequency possible and efficiency of the system, they have to be chosen based on a tradeoff between the cost, size, and performance of the design. A FET with lower RDS will reduce conduction losses, and lesser gate capacitance will reduce switching losses. The gate driver must be able to drive the gate capacitance of the FET at the switching frequency desired. If the gate driver isn’t powerful enough, the ramps rate could be too slow, causing the FET to operate in the inefficient linear region. If it’s too powerful, the FET could ring, producing electromagnetic interference (EMI) emissions.

MODULATOR

The modulator’s output provides the dimming signal to the hysteretic controller. A high output from the modulator produces constant current at the LED while a low output relates to zero current. The choice of modulation scheme should allow for a high degree of resolution to harness the potential of LEDs. As the human eye can perceive small gradients at lower intensity levels, an 8-bit modulation scheme will create undesirable and perceptible steps in an extended fade sequence. The higher resolution of a 12- to 16-bit modulator requires a clocking frequency that allows for a smoother gradient.

The modulator frequency must be high enough to allow for a refresh rate that is higher than the persistence of human vision. When using a 16-bit modulation at 700 Hz, the modulator must be clocked at 700 Hz × 65536 cnts ˜ 45 MHz. Today, different modulation schemes are available for driving LEDs. Pulse-width modulation (PWM) involves representing the desired dimming quantity as a ratio of width of the pulse to the period of the pulse. Additional modulation techniques such as precise illumination signal modulation (PrISM) spread the dimming quantity in a pseudorandom fashion throughout the period of the pulse. Such a stochastic signal density modulation scheme spreads the energy throughout the spectrum, reducing quasipeak emissions.

TRIP CIRCUITRY

Various scenarios require the driver element to halt the constant current hysteretic control loop. Operating under sudden input voltage fluctuations and temperature gradients can affect the longevity and performance of the LED engine. Trip circuitry comprising a programmable DAC and comparator can deliver the required logic signal to the hysteretic controller’s logical AND function.

Advances in semiconductor technology are allowing for integration of these components into fast shrinking and inexpensive programmable controllers. The PowerPSoC family of parts includes hysteretic controller channels that can be set up to create various topologies to drive HBLEDs. By coupling integrated drivers with an onboard microprocessor, the cost and form factor of a solution can be reduced with supplementary benefits associated with reduction in EMI emissions.

Optics for Hire is one of the leading companies having highly skilled and knowledgeable Ukrainian optical design consultants. The experienced team at Optics For Hire of designers and engineers are constantly working hard to meet the optics design needs of varied industries. Optical instruments are created for use in optical media, biomedical devices, illumination and imaging systems and metrology tools. The engineers of the Optics for Hire will sit with each client to understand their specific needs and based on the discussion will start with the designing work.

To Read (Part – I) Click Here.

The Five Building Blocks Of An Efficient, High-Brightness LED Driver (Part – I)

Five Building Blocks Of An Efficient LED Driver

As high-brightness LEDs (HBLEDs) penetrate all avenues of the lighting market, various semiconductor manufacturers are offering constant-current drivers. Only by choosing a driver IC capable of meeting the flexibility and control required by today’s applications can the true potential of HBLEDs be unleashed. Theatrical lighting, for example, often requires high dimming resolution while dynamically adjusting the current to account for fluctuating power sources and operating temperature. Since the quality of light output is intrinsically tied to the capability of the LED driver, it is important to choose a system that has the right specifications.

Today’s HBLEDs typically have a nominal current rating of 300 to 700 mA. As the envelope of light output is pushed, devices requiring more than an ampere are appearing in the market. In all LEDs, due to the voltage-current relationship and the binning approach used by manufacturers, a constant-current source is used for accurate control of the light output. Choosing the right constant-current regulator depends on the operating voltage of load and source, the desired efficiency, and the cost and size of the system.

A high-power resistor in series with LEDs would be the simplest form of current regulator. However, since it alone cannot adapt to changing source voltages or the non-linear VI characteristics of an LED, a closed-loop system that changes the resistance based on output current may be used. In either case, the energy not used by the LED is dissipated as heat by the linear regulator, leading to an inefficient system. In most HBLED applications, switching regulators offer better efficiency over a wide range of operating voltages.

HBLED lighting fixtures designed to replace incandescent and fluorescent bulbs must provide better efficiency and quality of light while maintaining low cost. An integrated switching regulator used in lighting applications must require minimal external components and have good current regulation.

DIFFERENT TOPOLOGIES

While switching regulators can have diverse forms, they all operate using the same principle of moving small and controlled quantities of energy from the source to the load. The type of topology that is chosen depends on the type of conversion that is required. A boost topology is used when source voltage is lower than the required load voltage, while a buck allows the source voltage to be greater than the load voltage and is typically used for driving LEDs.

The main control system in any buck regulator is the hysteretic controller. This block regulates the current through the inductor by turning on a switch when it is below the lower threshold and vice versa. A shunt resistor is a convenient method of sensing the current, and by pairing it with a differential current sense amplifier (CSA), a smaller resistance can be used to minimize power losses. The analog circuitry of the controller uses the feedback from the CSA. These blocks can be arranged in various combinations. Different LED colors differentiate the topologies.

In all three topologies, current flows through the inductor when the corresponding switch (field-effect transistor, or FET) is turned on. When the current rises above a predetermined limit, the hysteretic controller on each topology turns off the FET. As the current in the inductor persists, it conducts through the flyback diode until it falls below the lower threshold and the FET is turned on again. A system capable of faster switching will require smaller inductors to store magnetic flux between alternate cycles.

The topology with the red LED is configured with a low-side sense resistor located on the source pin of an N-FET. An inherent problem with this implementation is that current through the inductor can only be sensed when the switch is on. Once the current reaches the peak threshold and the switch is turned off, the hysteretic controller must use a timing circuit to turn the switch back on.

If during the off cycle the falling current does not reach the lower threshold or overshoots it, the off-time must be adjusted until the loop is stable at the required current ripple. As this technique has true hysteresis on only one side of the loop, it won’t be able to quickly adjust to fast transients of source and load conditions.

A hysteretic control system that can sense both falling and rising edges requires the feedback loop to remain in the current path regardless of the state of the switch. The topology used by the blue LED shows the sense element in the path of the inductor current in the charging as well as discharging phase. To achieve this, a high-side switch or P-FET is used. Because the RDS (resistance offered by the FET to current) is higher in P-FETs than in N-FETs, there is a loss in efficiency. Additionally, the high-side driver and the P-FET itself are generally costlier than a low-side driver and N-FET rated for the same switching capability. Finally, in the topology used by the green LED, the FET and sense resistor swap positions. This permits the use of an N-FET to increase efficiencies while the location of the sensing element allows inductor current to be sensed throughout the operation of the hysteretic controller.

Working as a system, the LED driver channel depends on five elements to create a topology that is efficient and robust while meeting the demands of HBLED applications: the hysteretic controller, the current sense amplifier, the gate driver and FET, the modulator, and the trip circuitry. The same blocks may be used for other topologies such as boost, buck-boost, and single-ended primary inductor convertor (SEPIC). To Read (Part – II) Click Here.

Article is posted by Optics For Hire – Optical Design Consultants

An Insight to Light Imaging Systems

A general theory of optical transport systems has been developed that can be used to determine preliminary design specifications for light guide systems. Several generic light guide types are analyzed, including hollow reflective light guides, prism light guides, solid dielectric and fluid-filled light guides, lens guides, and open light wells. Minimum theoretical aperture requirements are determined for each type as a function of the specified optical transport efficiency and design parameters (light guide length, transmitted luminous flux, etc). Generally, a system’s aperture requirement would be inversely related to its cost. Solid dielectric (e.g., optical fiber) light guides would be very compact and practical for retrofit applications, but their high cost option, but would require the greatest aperture area. Hollow reflective light guides, prism light guides, or lens guides may offer the best compromise between cost and space requirements. But in order to achieve optical concentrations and efficiencies near the theoretical limit, the collector system would need to maintain optical and tracking tolerances exceeding the capabilities of existing systems so further advances in core daylighting will require improvements in collector technology.

Principles of Light – Basic Theory:

Light is a form of radiant energy that travels in waves made up of vibrating electric and magnetic fields. These waves have both a frequency and a length, the values of which distinguish light from other forms of energy on the electromagnetic spectrum. Visible light, as can be seen on the electromagnetic spectrum, represents a narrow band between ultraviolet light (UV) and infrared energy (heat). These light waves are capable of exciting the eye’s retina, which results in a visual sensation called sight. Therefore, seeing requires a functioning eye and visible light.

Principles of Light - Basic Theory

Lighting Systems: Light can be produced by nature or by humans. “Artificial” light is typically produced by lighting systems that transform electrical energy into light. Nearly all lighting systems do so either by passing an electrical current through an element that heats until it glows, or through gases until they become excited and produce light energy. Incandescent light sources are an example of the first method, called incandescence. Current is passed through a filament, which heats until it glows. Because this method is considered wasteful (most of the energy entering the lamp leaves it as heat instead of visible light, other light sources were pioneered that rely on the gaseous discharge method, including fluorescent, high-intensity discharge (HID) and low-pressure sodium light sources.

A typical lighting system is comprised of one or more of these light sources, called the lamps. Fluorescent, HID and low-pressure sodium lamps operate with a ballast, a device that starts the lamp and regulates its operation. Lamps and ballasts in turn are part of the luminaire, or light fixture, which houses the system and includes other components that distribute the light in a controlled pattern.

Designing the Lighting System: To produce a new lighting system in a construction or renovation scenario, it must be designed. The designer must determine desired light levels for tasks that are to be performed in a given space, then determine the light output that will be required to meet those objectives consistently, taking into account all the factors that degrade both light output and light levels over time. Equipment must then be chosen and placed in a layout to produce the desired light distribution. The designer must also consider a range of quality factors in his or her design choices and equipment selection, including color, minimizing glare, safety and if required, aesthetics.

Managing the Lighting System: To properly manage an existing system, many types of professionals may be involved, from electrical contractors to facilities manager – – for our purposes in this case, we will call them lighting managers. The lighting manager must ensure that the existing lighting system consistently provides the most effective lighting at the lowest operating and maintenance cost. This may entail retrofitting or upgrading the system to reduce energy costs and/or increase performance, a planned maintenance program to keep the system operating at peak performance, and other activities that will ensure that the lighting system is continuously doing its job.

Article is posted by Optics For Hire

An Insight to Illumination Design

The design of illumination systems is as much of an art as it is science. Illumination engineering, or designing, is a challenging, and very rewarding field that transforms the output of a simple bulb (or LED) into a pattern of illumination that allows us to work, drive or play safely. As engineering evolves into design, the designer combines fundamental physics with architectural aesthetics and human physiology to develop lighting solutions to satisfy all of our ever changing needs. A combination of environmental considerations, energy savings goals and technology advances are helping to bring about significant changes in the field of illumination design. Illumination systems cover a broad range of applications, with an equally broad range of design specifications and requirements. It may be a small task lamp that needs to provide a reasonably uniform patch of light to a desktop work area or it could be the headlamp of an automobile which needs to adequately illuminate the path ahead for the driver without blinding a driver approaching from the opposite direction. Good lighting can be described with a simple set of basic requirements, such as the amount of light needed, the uniformity, and color appearance or it may be defined by regulations such as FVMSS or ECE lighting codes.

The Complete Design Solution for Illumination Applications: You can design accurate, cost-effective illumination optics with Optics For Hire. Its unique design and analysis capabilities, combined with ease of use, support for rapid design iterations and automatic system optimization help to ensure the delivery of illumination designs according to specifications and schedule.

Smart system modeling with full optical accuracy and precision: You can also create designs easily with 3D solids that can be inserted into the model at any size, in any location and at any orientation. Geometry is always editable using Boolean and trimming operations that retain the optical accuracy of surface shape, position and intersection for all calculations.

Rapid evaluation of optical behavior during design iterations: With point-and-shoot ray tracing, you gain an instant understanding of the system’s optical behavior by graphically starting and aiming rays from any point in the model. Rays are displayed visually and updated automatically as the model is changed and they can be moved and rotated interactively to study the behavior of a model.

Quick convergence on the design that best meets your goals: You get improved system performance automatically with the most effective illumination optimization algorithms available. Optics For Hire fully integrated optimization capabilities combine design and analysis features to allow you to optimize any aspect of your system to meet performance goals. For example, optimize a system to match a target illumination distribution while simultaneously maximizing total power.

Application Areas of Illumination Designing: Design and Simulation of

  • LED Lamp
  • Displays
  • Light pipes
  • General Lighting
  • Solar
  • Automotive Lighting
  • Stray light simulation
  • Projectors Headlamps
  • Photorealistic

An Insight to CODE V Optical Design

CODE V optical design software

CODE V optical design software is used to model, analyze, optimize, and provide fabrication support for the development of optical systems for diverse applications. It provides a powerful and yet easy-to- use toolkit of optical techniques and calculations that enables you to create superior designs that will work right when built. CODE V is the most powerful software for Optical Imaging System Design.

Since its worldwide introduction in 1975, CODE V has been instrumental in the development of highly advanced optical systems, sometimes with profound effects on business and culture. It has been used in the development of revolutionary applications such as the compact disk player. CODE V algorithms are a key and dominant technology in the design of the micro-lithographic lenses that permit the imaging of ultra-fine lines on computer chips—a necessary ingredient in the continuing improvement of computer speeds.

Applications: From the extreme UV to beyond the infrared and from consumer products to government hardware, CODE V will handle your optical imaging applications. CODE V’s state-of- the-art algorithms, user-friendly interface and intelligent defaults speed time to market and maximize the quality of your optical solution.

Some applications and related CODE V features include:

  • Injection molded plastic lenses— environmental analysis and material tolerances
  • Grating spectrometers — wavelength dependent multiconfiguration features
  • Digital camera lenses — tolerance and fabrication analysis features
  • High-NA lithography optics — polarization ray tracing
  • Reconnaissance lenses — glass optimization with partial dispersion control
  • Telescopes and other visual systems — true afocal modelling
  • Space-borne systems — environmental analysis
  • Laser scanning systems — diffraction beam propagation analysis
  • Infrared and UV systems — special material characterization
  • Telecommunication systems — fiber coupling efficiency computations
  • Segmented aperture systems — non-sequential ray tracing features