Tag Archives: LEDS

Future of LEDs

LEDs have much to offer—small size, high efficiency, and incredible versatility—no wonder they are the most popular electronic products in the market today. Their versatility allows us to use them in horticulture, as status indicator lights, and displays with high definition. Although we are so familiar with LEDs that we hardly notice them anymore, new applications keep appearing, and engineers are forever making newer breakthroughs. That is why the LED market is still growing at a stupendous rate, especially in Europe, India, and Southeast Asia. We have listed some new technologies here:

Multicolor LEDs

After several tries, scientists have recently been able to achieve an LED that produces a blue color. This has completed the entire spectrum of LED arrays. Now, scientists have a technique that allows a single LED to produce all three primary colors. So far, rendering a full spectrum required placing three to four tiny LEDs near one another. The new technique has a big implication of making multicolored displays with color-tuned LEDs.

Furthermore, the new process dopes gallium nitride with europium, a rare earth element, and the process is compatible with current technologies involving GaN. Commercial solid-state lighting commonly uses GaN LEDs, which means we will see the new technology working in the commercial sector very soon.

Cooling with Reversed LEDs

LED physics has another significant new development. Running LEDs in reverse creates a cooling effect. A research team has demonstrated that by running LEDs backward, it is possible to achieve a tiny cooling effect of the order of 6W/m2. This is contrary to the situation in a reverse connected diode, where the diode does nothing.

Researchers are of the opinion they can improve the cooling capacity to 1000W/m2. Although the idea is not yet ready for practical implementation, wearables and mobile devices may benefit from the improved performance from using LEDs to remove heat from processors.

Lighting for Horticulture

Horticulture is benefitting from LED temperature effects and color-tuned lighting. Tomato growers in Belgium have used LEDs to stimulate plant growth. Rather than high-pressure sodium vapor (HPSV) lamps, as is the industry standard, the farmers used LED lighting for their entire 13.3-acre indoor tomato farm.

Although the light from the LEDs appears pink to human eyes, it is actually a mix of red, infra-red, blue, and white LED lights, which the farmers have mixed perfectly for stimulating tomato plant growth. Using Hyperion fittings, the farmers have used new LEDs from Cree. Now, farmers in the UK and the Netherlands are also using these new horticultural LED lamps.

The Belgian farmers were initially skeptical about using LEDs, as these have high efficiency and produce greater amounts of light than heat. They felt LED lights will not provide adequate heat during winter to keep the plants warm. However, they did not need their back-up heating system in the first winter. This proves developments in lighting is effectively reducing payback periods.

The future for LEDs looks bright, with new sources of innovation and recent technological development bringing increasingly superior practical use. Expect more new and improved products in our daily lives with these new LEDs, especially those in color tuning.

Role of LEDs in Horticulture

While LEDs have revolutionized indoor and exterior lighting methods, they have been revolutionizing operations involving indoor grow facilities. This is mainly because LEDs are highly flexible in their spectral output, while their efficiency is very high. That means they emit much lower heat.

A new standard from ASABE specifies the performance of LED lighting products for horticulture applications. The standard spells out the test methods to measure the optical radiation from LEDs in the range 280-800 nm. Note the visible spectrum covers about 390-700 nm.

According to the Standards and Technical director of ASABE, Scott Cedarquist, in horticultural applications, LED lighting has generated very high levels of interest in their projects in the last 20 years. Therefore, horticultural lighting makes use of several terminologies that are primarily focused on plants. Two of them are PPFD or Photosynthetic Photon Flus Density and PPF or Photosynthetic Photon Flux.

While PPFD measures the number of active photons falling on a surface per unit area per unit of time, PPF is the number of photons created by a lighting system per second.

Horticultural lighting primarily focuses on delivering photons that initiate photosynthesis and other processes in plants. These spur plant development as they excite electrons. Horticultural applications use LED products that are different from those used for general illumination. The difference is primarily that the former has a wider spectral output typical for horticultural applications. This is necessary as different plants respond differently to various wavelengths.

According to academic and industry research, each type of plant has a specific light recipe that helps the plant to yield higher growth in the shortest period. The recipe holds the variation in optical spectra for optimizing the overall growth of the plant, thereby improving desirable plant characteristics. For instance, increasing the potency of cannabis or the flavor of vegetables.

The light output from LEDs has another characteristic. Not only do LEDs provide a precise output spectrum, but this spectrum can also be tuned to optimize the spectrum for different plants and the phases of their life.

LED lighting products are primarily used in horticulture as vertical farms. This is due to the far lower heat output from LEDs as compared to that from other light sources. This allows the LEDs to be interspersed very close to the plants without damaging them. Therefore, facility managers are able to maximize the use of available space. This has made vertical farming very popular in urban areas. Horticulturists are making use of abandoned buildings which they are converting to grow food, thereby making new products available at cheaper rates.

The high efficiency of LEDs also helps considerably in energy savings. However, grow facility managers are more interested in the yield of the crop, and use of LEDs for high-value crops such as cannabis offer revenue increase from higher yield and shorter life cycle, rather than from energy savings. Similarly, more traditional crops such as flowers and leafy vegetables also use LED lighting not for energy savings, but rather for the ability to produce more crops in a shorter period.

Lighting for Illumination and Indication

In our industries, lights play several important roles. Primarily, industries tend to use lights for two fundamental purposes—illumination and indication. Smart visual factories use lighting intelligently. They carefully differentiate between using it for illuminating devices and for indicating them.

Fixtures for illumination light up a space in the industry, improving productivity, worker ergonomics, and enhancing safety. For instance, in huge storerooms, low bay lights illuminate areas blocked by structures shielding ceiling or high bay lights. Another example is the use of task lights that offer bright and focused light required to perform finer tasks at workstations, such as inspection or assembly. Furthermore, operators can visually monitor machine processes and examine interiors of enclosures using heavy-duty machine lights.

On the other hand, the industrial use of indication devices provides visual status updates. For instance, an indicator light at a station lets a manager know he or she is needed there. A machine alerts an operator with an indicator light regarding material refilling or a jam. Indication devices often use stack or tower lights, with each segment indicating a different status when it lights up. A change of colors and/or a flash in domed indicator lights often indicates a change in status.

So far, industries had managed to keep the two categories distinct. However, with the advent of LED lights, manufacturers are trying to combine illumination with indication and merging them into a single flexible device. For instance, strip lights for illumination purposes so far, were using only white light. Now they use RGB LED lights that normally give off a white color, but they can also modify the lights to show different statuses by giving off multiple colors. The device therefore, is suitable for ambient or task lighting with white light, but can also indicate status with colored light.

Industries are now using multicolored LED strips in the sightline of operators to provide them with unambiguous status indication, while using the same in tower lights to offer the supervisors an indication at a glance.

By combining illumination with indication, machine builders not only enhance the visual appeal of their machine, and improve its functionality, but the sleek and colorful lights also offer tangible benefits to their customers. Advantages include faster response to status change promotion, improved ergonomics and limited waste movements, ensuring the addressing of critical status updates in a timely fashion, and reducing the risk of expensive accidents and mistakes.

The combination of illumination and indication devices is convenient for not only OEMs but their customers as well. As the combined devices fit easily into the framework of the machine, which protects them, they are effective in their function. Retrofitting an existing machine with a combined indication and illumination device is easy, as only a single device needs setting up, and fitting only a few wires achieves both the functions. The industry is using such combined devices in applications involving machine lighting, workstations, intersections shared by foot traffic and mobile equipment, automatic gates, overhead doors, and for collaborative robots.

The combined indication and illumination devices are providing both OEMs and end users with exciting new possibilities. Although started as a trend, the combined devices are proving their worth in industrial applications.

How Efficient are Light Emitting Diodes – LEDS?

Almost all commercial and residential establishments are moving over to light emitting diode (LED) illumination, as they are guaranteed to be more efficient compared to other forms of lighting such as incandescent and fluorescent. Unless designed with care, LEDs can suffer from premature failure due to thermal issues. Under thermal stress, LEDs can permanently lose their brightness, while degrading much quicker than the manufacturer intended. That means designers and engineers need to balance the additional cost of emitters with the thermal design for providing not only an elegant design solution, but also the long life that solid state lighting promises.

With roughly 50% of the electrical energy produced worldwide being used for lighting, and the world population growing, the only two alternatives to meet the growing needs of energy are to either generate more or to make more efficient use of what we already have. Generating more energy can take several years to plan and install power plants, but improving the efficiency of lighting can effectively mitigate the rising trend of power consumption.

Providing over 100 lumens per watt, LEDs are being increasingly used for a large selection of general applications. When converting fixture designs for incandescent bulbs to those for LEDs, engineers faced issues because of the difference of their thermal characteristics. For instance, manufacturers publish the life curves for LEDs as a function of temperature, while fixture designers do not know how to handle the information.

Incandescent bulbs were actually heaters that emitted some visible light. Nearly 90% of the light emitted by incandescent bulbs fell into the region beyond 700 nanometers—the infrared region—invisible to the human eye, but perceptible as heat. This would often cause problems in the kitchen, with waste IR light promoting premature spoilage in food illuminated by incandescent bulbs.

LEDs produce light via a different mechanism. When electrons in the LED junction cross over a forbidden energy zone called band-gap and combine with holes, they produce light because the electrons lose energy. Physicists tailor the energy by adjusting the width of the band-gap, thereby producing various frequencies of light. For instance, a white LED actually generates intense blue or Ultra Violet light, which then excites a phosphor placed in its optical path, thereby turning it into white light.

However, the process of converting electrons to light photons within the junction of the LED is not a perfect one. A vast majority of the photons created within the junction is never emitted and ultimately recombine to produce waste heat. Additionally, Stokes Shift, the phenomenon that shifts the frequency of the LED emission in the phosphor to produce white light, also generates waste heat. Waste heat from both of these mechanisms must be removed from the LED junction to prevent severe damage.

Unlike their incandescent predecessors, LEDs rarely fail catastrophically. Their slow degradation affects the photon emission mechanism, resulting in a dimming effect. Engineers use two industry end-of-life metrics for measuring the life of LEDs. One is the L70 or time taken to reach 70% of original emission, and the other is L50 or time taken to reach 50% of the original emission. The industry uses the L70 point as the useful life of an LED fixture or bulb.

Intelligence in LED Lighting

Apart from illuminating dark spaces there is much more to LED lighting than otherwise thought of. LEDs can be connected in an intelligent network with a low-voltage IP-based infrastructure, and they become a part of a powerful network of systems. Such a system can cooperatively collect, analyze, manage, control, and respond to specific objectives based on real-time sensor feedback.

The building lit up by these LEDs now behaves as a smart building, offering better operational performance. It responds dynamically to operating issues related to power consumption and cost, increasing efficiency and efficacy. Moreover, such integrated intelligent lighting works smoothly with the other systems in the building.

The major issue confronting LED networks is decoupling from the relatively universal approach of a centralized lighting control. It makes more sense to change over to a solution that caters to the specific requirements of smaller segments across a large area within the building. Moreover, as lighting is a part of the intelligent network, it can integrate with and respond to other components on the network. Such an approach works very well for commercial office buildings, warehouses, healthcare facilities, manufacturing and industrial facilities, and other similar large or multipurpose areas, where a centralized approach will be inefficient and ineffective.

As an example, buildings are very commonly controlled through automated heating, ventilation, and air conditioning−also called the HVAC system. The HVAC has the task of monitoring and adjusting the temperature to make the building suitable for human comfort and machine performance. Moreover, it does this at optimal efficiency and cost. An intelligent LED lighting network connected to the system would allow lighting to synchronize into the same set of objectives. Now, the lighting couples actively and responds to environmental climate control.

This gives the lighting network the intelligence to increase the ability of users to adjust the light within the building to increase human productivity, concentration, positive mood, and well-being. Moreover, by adjusting light synchronized to the natural circadian cycle and adjusting the amount of light required depending on the amount of sunlight filtering through external windows, additional potential advantages can be achieved.

All intelligent LED lighting networks need power, and the key technology behind this is Power over Ethernet (PoE). This brings the equipment and low-voltage cabling necessary to connect the assets of Internet of Things (IoT) to LED fixtures. The success of IP-based infrastructure platforms makes PoE simple and available. Therefore, by using PoE as the arteries of the LED lighting systems for power and control, lighting also becomes a part of the building’s IoT asset.

PoE provides an infrastructure that is less expensive compared to copper cables, while offering a single layer for transferring power and data. Typically, the PoE system architecture consists of the PoE gateways, LED light fixtures, LED lights, smart drivers for LEDs, cable harnesses, sensors, wireless switches and dimmers. In general, PoE gateways are configured to use any one source from unregulated 48 VDC, constant voltage 24 VDC/48 VDC, or constant current.

There may be wireless PoE gateways as well, conforming to IEEE 802 standards. Usually, they run at standard frequencies such as 902 MHz in the North Americas, and at 868 MHz in Europe.

Charlieplexing on the Raspberry Pi

If you suddenly find the need to control many LEDs and do not have the requisite electronics to do so, you can turn to your single board computer, the Raspberry Pi (RBPi) and use it to charlieplex the LEDs.

Charlieplexing is named after Charlie Allen, the inventor of the technique. Charlieplexing takes advantage of a feature of the GPIO pins of the RBPi, wherein they can change from outputs to inputs even when the RBPi is running a program. Simply setting a GPIO pin to be low does not allow enough current to pass through an LED or influence the other pins set as outputs and connected to the LED.

Using Charlieplexing, you can control up to six LEDs with three GPIO pins. For this, you will need three current limiting 470Ω resistors on each GPIO pin. The program charlieplexing.py defines a 3×6 array, which sets the state and direction of the three GPIO pins. The state defines whether the pin is set as digitally high or low, and the direction defines whether the pin is an output or an input.

Since LEDs are also diodes, they will light up only if their anodes are at a higher potential than their cathodes are, and not otherwise. Therefore, to light up a single LED, the program has to set the pin connected to its anode as output and drive it high. Next, the program must set the pin connected to the anode of the LED as input, while it sets the third pin as output and drive it low. Various combinations of the state and direction of the pins will drive all the LEDs on and off sequentially.

The array in the program holds the settings for each GPIO pin. A value of 0 means the pin is an output in a low state, 1 means the pin is an output in a high state, and -1 means the pin is set as an input.

In charlieplexing, it is easy to calculate how many LEDs each GPIO pin can control. The formula for this is, LEDs = n2-n, where n is the number of pins used. According to the charlieplexing formula, three GPIO pins can charlieplex 6 LEDs; four pins can control 12 LEDs, while 10 pins would allow control over a massive 90 LEDs.

Charlieplexing is good for not only lighting one LED at a time, but it is capable of lighting more at the same time also. For this, the program must run a refresh loop to keep the desired state of the LEDs in the array. While refreshing the display, the program must turn on other LEDs that need to be on, before moving on to the next. However, persistence of vision plays a large part here, and the program must be sufficiently fast to make it appear that more than one LED is on at a time.

However, there is a downside to lighting more LEDs at a time. Since more number of LEDs are now on to make it appear that more than one LED is on simultaneously, each LED is actually lit for a lower amount of time, which makes each LED glow less than at its full brightness.

Dimming LEDs with PWM Generator

nlike incandescent bulbs, dimming Light Emitting Diodes (LEDs) is not an easy task. Incandescent bulbs operate on alternating voltage supply, whereby using Triacs, one can control the effective RMS voltage applied to the bulb. Moreover, since the incandescent bulbs are resistive elements, a simple reduction is voltage is sufficient to reduce the current through it, thereby reducing its light and heat output.

LED operation is different, as they work on direct voltage. Each LED requires an optimum load current to produce light, while dropping a fixed voltage across its terminals. Therefore, it is impossible to dim the LED light output by decreasing the voltage across it or by limiting its current load.

However, an LED responds much faster, switching on and off at a much higher speed than an incandescent bulb does. This feature allows switching an LED on/off rapidly to change its light output. For instance, if the LED is repeatedly switched on for the same amount of time that it is switched off, the resultant average intensity from the LED is halved. By continuously changing the ratio of the on-to-off period, the LED can be made to traverse from zero output to its maximum light output. Engineers call this technique the Pulse Width Modulation (PWM), and this has become the de facto mechanism for dimming LEDs.

Linear Technology makes different types of PWM controllers for LEDs, and they have designed the LT3932 for dimming a string of LEDs efficiently. A monolithic, synchronous, step-down DC/DC converter, the LT3932 utilizes peak current control and fixed-frequency PWM dimming for a number of LEDs connected serially.

The user can program the LED current of the LT3932 using an analog voltage, or control its duty cycle of the pulses from the CTRL pin. A resistor divider on the FB pin of the LT3932 sets its output voltage limit.

One can use an external clock at the SYNC/SPRD pin of the LT3932 to control the switching frequency, which is programmable from 200 KHz to 2 MHz. Alternatively, an external resistor connected to the RT pin can also serve the same purpose. To reduce EMI generated by the switching frequency, the LT3932 features an optional function of frequency modulation involving spread spectrum that varies the frequency from 100 to 125%.

The LT3932 features an external high-side transistor rated for 3.6-36 V, 2 A, and a synchronous step-down PWM LED driver for dimming an LED string. This uses an internal signal generator for controlling the analog PWM dimming in the absence of an external PWM signal. LT3932 regulates the LED current to ±1.5%, while regulating the output voltage to ±1.2%. The IC achieves a 5000:1 PWM dimming at 100 Hz, and the internal PWM achieves a 128:1 dimming ratio with a maximum duty cycle of 99.9%.

The LT3932 protects the LED string from open/shorts while offering fault indication, as it has an accurate LED current sensor with a monitor output. Along with thermal shutdown, the IC features an accurate under voltage lockout threshold and an open-drain fault reporting for open circuit and short-circuit load conditions. With its silent switcher topology, the LE3932 is well suited for several applications including automotive, industrial, and architectural lighting.

Blinkt! is Compatible with the Raspberry Pi

If you are interested in learning how to control RGB LEDs with the Raspberry Pi (RBPi) single board computer, Blinkt! provides a simple way to interface. Blinkt! is a strip of eight superbright RGB LED lights that you can connect to the RBPi without wires, so it is an easy way to start. Blinkt! Has a female connector that matches the male GPIO connector on the RBPi, and that allows the tiny LED board to sit atop the RBPi.

The RBPi can individually control each of the eight APA102 RGB LEDs on the Blinkt! board individually, so you can consider them as matrix of 1×8 pixels. The footprint of the board is tiny enough to allow it sit directly on top of the RBPi and the pair fits inside most of the Pi cases. Although the RBPi controls the eight LEDs with PWM, it does not interfere with the SBC’s PWM audio. Blinkt! comes fully assembled and is compatible with RBPi models 3, 2, B+, A+, Z, and ZW. Pimoroni, the manufacturers of Blinkt!, also provide a Python library for the users.

Combining Python programming and Blinkt! with the RBPi is a great way of understanding how RGB LEDs work and how a computer program controls their operation.

If you are using the RBPi3 for this project, it will already have the male GPIO on the board. However, the RBPiZ and RBPiZW may not have the connector, which means you may need to solder the connector to the board. You need to be careful when plugging the Blinkt! board onto the RBPi taking care to orient it in the right way. The Blinkt! board has rounded corners on one of its side, and this side should face the outside of the RBPi. Once you align the boards properly, push the Blinkt! board in and it should fit snugly on the RBPi.

To make the RBPi control the LEDs on the Blinkt!, it will need to have the right code. The best way to begin is to update the Operating System of the RBPi to the latest Raspbian. Once you have done this, and the RBPi is running, connect it up to the Internet and open the terminal on the RBPi screen.

Typing the code “curl https://get.pimoroni.com/blinkt | bash” without the quotes, should allow the RBPi to download the necessary Python libraries from the Pimoroni website. Now you can use the Python 3 IDLE code editor to use the library to write the Python program and control the LEDs.

While writing the Python program, you will need to begin by importing the Blinkt! library you had downloaded in the first step. Each LED is termed as a pixel so the parameter “set_pixel” allows you to address a specific LED, while “set_brightness” allows setting its brightness. The command “show” turns on the specific LED, and “clear” turns it off.

Even though the LEDs are numbered as 1 to 8 on the board, the program addresses them as 0 through 7. Therefore, the program can pick a light and tell it the color it needs to be, its brightness, and whether it should turn it on or off.

What is a QLED?

Recently, Samsung has announced their new TV technology using QLEDs to counter the OLED TVs that LG and others have put on the market. QLED stands for Quantum dot LED, and though Samsung has been using the concept of quantum dots in its TVs for quite some years now, they claim they will be bringing out several flavors of the QLED technology.

According to Samsung, QLEDs are transmissive, as LCDs are, and light goes through several layers to create an image on the surface of the screen. The company claims to be working on the ability of the QLEDs to overcome the challenges currently plaguing the OLEDs.

Although the Q part is currently demanding a premium in the price of Samsung TVs on the market, it will likely decrease in the future. According to Samsung, the QLEDs are bringing several advantages with reference to picture quality, such as higher light output and brighter colors. Samsung claims the light output in highlights is now 2,000 nits, a relative quick loss of peak luminance, and improvement of the delayed ramp-up.

Samsung compares their QLED performance with OLEDs and points out that the new quantum dots offer superior color, providing rich, fully saturated colors even for bright images. However, there is yet no independent testing to substantiate the claims of the company. Moreover, the claims cover only the high-dynamic range as against the standard dynamic range, where the OLED would be a superior performer.

While many observers claim to see better clarity and improved colors in the new TV technology, others fail to notice any difference. You can see QLEDs in Samsung TV model UE55KS9000, and in tablets such as Amazon Kindle Fire HDX 7, and HDX 8.9.

QLEDs contain quantum dots or microscopic molecules between two and 10 nanometers in diameter, which emit their own, differently colored light according to their size, when struck by photons or light particles. In the QLED TVs from Samsung, the dots are restricted to a film, and the LED backlight provides the illumination to light them up. This light then goes through other layers inside the display, which includes an LCD layer, ultimately creating the picture. As the light from the LED source passes through different layers before reaching the screen surface, the process is said to be transmissive.

The advantage of QLEDs is they can emit brighter, more vibrant, and more diverse colors—capable of making HDR content really shine—mainly due to their ability to achieve high peak brightness levels.

Compared to OLED TVs, it is more cost-effective to manufacture quantum dot TVs, which translates to better picture quality at a lower price. However, OLED displays still produce the deepest blacks, which means that OLEDs offer better contrast ratios. Therefore, while OLEDs offer true blacks, quantum dots offer great bright images.

QLED technology replaces the photoluminescent quantum dots with electroluminescent nanoparticles. Therefore, rather than coming from the LED backlight, light now comes directly to the display. Although the process is a lot similar to the light transference process within an OLED TV, within the QLED TV, individual pixels emit the light, thereby combining the best of quantum dots and OLED technology.

Multicolored LEDs Create Secondary Colors

Any student of physics knows mixing two primary color light sources produces a secondary color. For instance, mixing the primary colors red and green creates the secondary color yellow. There are three primary colors—Red, Blue, and Green. This process is easily seen in tricolor and RGB LEDs.

There is a disadvantage in this method. As two primary colors are necessary for generating a secondary color, two LEDs must remain turned on at the same time. Therefore, generating a secondary color means consuming twice the current a primary color requires. In battery powered circuits, the operating current of the LED indicator may be a significant fraction of the total current, and using the same current for generating both primary and secondary colors would be an advantage.

Using a sequencing method can generate balanced secondary colors from RGB, tricolor and bicolor LEDs, while using the operating current of a single LED. The sequencing method offers uniform intensities between the primary and secondary colors, and lower power dissipation. An added advantage of using the sequencing method with bicolor LEDs is keeping a simple pc-board layout with two pins while it produces three colors. Using the sequence method with RGB LEDs produces white light while consuming the operating current of a single LED.

The sequencing method works because it takes advantage of a property of the human eye. This is called persistence of vision, wherein images in the human eye persist for about sixty milliseconds after light from the object ceases to enter the eye. For instance, when a glowing coal is moved about in the dark, the eye sees a continuous red line.

When the human eye sees different primary colors flashed sequentially and quickly from one point, they appear to overlap in time, while the brain interprets the colors to be secondary colors, or, depending on the color components, even white.

Experiments with multiple primary-colored LEDs show that the above flash sequence should repeat every 25 milliseconds or lower, for the eye to treat the effect as a solid secondary color. In fact, the flash rate can go down to one microsecond, before the human eye can detect the degradation of the secondary color. Therefore, any clock source, say a convenient 40 Hz, should be adequate for creating secondary colors.

For the eye to properly see the mixed colors, the primary-color LEDs must be physically very close together, such as on a semiconductor chip. As an added advantage, diffused lenses are better, as this offers a wider viewing angle.

When using bicolor LEDs, the driver has to be bidirectional, as the LEDs are placed back-to-back in the chip. Moreover, currents for the three LEDs may have to be adjusted to achieve color balance between the primary and secondary colors. In addition, color balancing may be required also as LEDs have different intensities and efficiencies as the human eye sees them.

This correction can be done in one of two ways. As each LED has a current limiting resistor in series, the value of these resistors may be tweaked to achieve the necessary differentiation in individual currents. The other option is to keep the same current but tweak the duty cycle.