FOR THE LOVE OF FOOD- DOCUMENTARY AVAILABLE ON-LINE!
And there is no reason of keeping data without knowing its relevance to your business. You could hang a combination key lock box on the door handle or hide it in between large stones or bricks behind a bush. Customer restrooms, one for each gender, are required in all food establishments that offer 10 or more seats to the public for consumption of food or drink that is prepared on the premises. Foot-candles tell us how much of that light is directed at an object we want to illuminate. You can also partner up with different businesses that sell different kinds of foodstuffs, such as baked goods i. The tunability of emission wavelengths and narrow bandwidth is also beneficial as excitation sources for fluorescence imaging.
The yellow phosphor in LEDs is Cerium doped YAG crystal, in powder form and may be suspended in plastic, epoxy, synthetic rubber or silicone. Touching bare LEDs using synthetic rubber or silicone can damage the delicate wire bonds from LED to package or the LED itself, so they may be protected by a plastic or glass cover, such as in the LED flash in smartphones. Because of metamerism , it is possible to have quite different spectra that appear white.
However, the appearance of objects illuminated by that light may vary as the spectrum varies, this is the issue of color rendition, quite separate from color temperature, where a really orange or cyan object could appear with the wrong color and much darker as the LED or phosphor does not emit the wavelength it reflects.
The best color rendition CFL and LEDs use a mix of phosphors, resulting in less efficiency but better quality of light. Though incandescent halogen lamps have a more orange color temperature, they are still the best easily available artificial light sources in terms of color rendition. White light can be formed by mixing differently colored lights; the most common method is to use red, green, and blue RGB.
Because these need electronic circuits to control the blending and diffusion of different colors, and because the individual color LEDs typically have slightly different emission patterns leading to variation of the color depending on direction even if they are made as a single unit, these are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors,  and in principle, this mechanism also has higher quantum efficiency in producing white light.
There are several types of multicolor white LEDs: Several key factors that play among these different methods include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency means lower color rendering, presenting a trade-off between the luminous efficacy and color rendering.
However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. One of the challenges is the development of more efficient green LEDs. The theoretical maximum for green LEDs is lumens per watt but as of few green LEDs exceed even lumens per watt. The blue and red LEDs approach their theoretical limits. Multicolor LEDs offer not merely another means to form white light but a new means to form light of different colors.
Most perceivable colors can be formed by mixing different amounts of three primary colors. This allows precise dynamic color control. As more effort is devoted to investigating this method, multicolor LEDs should have profound influence on the fundamental method that we use to produce and control light color. However, before this type of LED can play a role on the market, several technical problems must be solved. These include that this type of LED's emission power decays exponentially with rising temperature,  resulting in a substantial change in color stability.
Such problems inhibit and may preclude industrial use. Thus, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists. However multicolor LEDs without phosphors can never provide good quality lighting because each LED is a narrow band source see graph.
LEDs without phosphor while a poorer solution for general lighting are the best solution for displays, either backlight of LCD, or direct LED based pixels. Feedback loop systems are used for example with color sensors, to actively monitor and control the color output of multiple color mixing LEDs. Depending on the original LED's color, various color phosphors are used. Using several phosphor layers of distinct colors broadens the emitted spectrum, effectively raising the color rendering index CRI.
Phosphor-based LEDs have efficiency losses due to heat loss from the Stokes shift and also other phosphor-related issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue as modeled in the luminosity function.
Due to the simplicity of manufacturing, the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.
Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor. Conformal coating process is frequently used to address the issue of varying phosphor thickness.
Alternatively, the LED might be paired with a remote phosphor, a preformed polycarbonate piece coated with the phosphor material. Remote phosphors provide more diffuse light, which is desirable for many applications. Remote phosphor designs are also more tolerant of variations in the LED emissions spectrum. Cu, Al that emits green. This is a method analogous to the way fluorescent lamps work. Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better.
Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin. Another method used to produce experimental white light LEDs used no phosphors at all and was based on homoepitaxially grown zinc selenide ZnSe on a ZnSe substrate that simultaneously emitted blue light from its active region and yellow light from the substrate.
A new style of wafers composed of gallium-nitride-on-silicon GaN-on-Si is being used to produce white LEDs using mm silicon wafers. This avoids the typical costly sapphire substrate in relatively small or mm wafer sizes. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant.
LED companies shifting from using sapphire to silicon should be a minimal investment. In an organic light-emitting diode OLED , the electroluminescent material composing the emissive layer of the diode is an organic compound.
The organic material is electrically conductive due to the delocalization of pi electrons caused by conjugation over all or part of the molecule, and the material therefore functions as an organic semiconductor. The potential advantages of OLEDs include thin, low-cost displays with a low driving voltage, wide viewing angle, and high contrast and color gamut. Quantum dots QD are semiconductor nanocrystals with optical properties that let their emission color be tuned from the visible into the infrared spectrum.
This provides more color options and better color rendering than white LEDs since the emission spectrum is much narrower, characteristic of quantum confined states. There are two types of schemes for QD excitation. The other is direct electrical excitation first demonstrated by Alivisatos et al. One example of the photo-excitation scheme is a method developed by Michael Bowers, at Vanderbilt University in Nashville, involving coating a blue LED with quantum dots that glow white in response to the blue light from the LED.
This method emits a warm, yellowish-white light similar to that made by incandescent light bulbs. In February scientists at PlasmaChem GmbH were able to synthesize quantum dots for LED applications and build a light converter on their basis, which was able to efficiently convert light from blue to any other color for many hundred hours.
A layer of quantum dots is sandwiched between layers of electron-transporting and hole-transporting materials. An applied electric field causes electrons and holes to move into the quantum dot layer and recombine forming an exciton that excites a QD.
This scheme is commonly studied for quantum dot display. The tunability of emission wavelengths and narrow bandwidth is also beneficial as excitation sources for fluorescence imaging. In February , a luminous efficacy of lumens of visible light per watt of radiation not per electrical watt and warm-light emission was achieved by using nanocrystals.
The main types of LEDs are miniature, high-power devices, and custom designs such as alphanumeric or multicolor. They usually do not use a separate heat sink. The small size sets a natural upper boundary on power consumption due to heat caused by the high current density and need for a heat sink. Often daisy chained as used in LED tapes.
Common package shapes include round, with a domed or flat top, rectangular with a flat top as used in bar-graph displays , and triangular or square with a flat top.
The encapsulation may also be clear or tinted to improve contrast and viewing angle. It is made of two-dimensional 2-D flexible materials. It is three atoms thick, which is 10 to 20 times thinner than three-dimensional 3-D LEDs and is also 10, times smaller than the thickness of a human hair.
These 2-D LEDs are going to make it possible to create smaller, more energy-efficient lighting, optical communication and nano lasers. Some can emit over a thousand lumens. Since overheating is destructive, the HP-LEDs must be mounted on a heat sink to allow for heat dissipation. For each half-cycle, part of the LED emits light and part is dark, and this is reversed during the next half-cycle.
Flashing LEDs are used as attention seeking indicators without requiring external electronics. In diffused lens LEDs, this circuit is visible as a small black dot. Most flashing LEDs emit light of one color, but more sophisticated devices can flash between multiple colors and even fade through a color sequence using RGB color mixing.
There are two types of these. One type consists of two dies connected to the same two leads antiparallel to each other. Current flow in one direction emits one color, and current in the opposite direction emits the other color.
The other type consists of two dies with separate leads for both dies and another lead for common anode or cathode so that they can be controlled independently. Each emitter is connected to a separate lead so they can be controlled independently. A four-lead arrangement is typical with one common lead anode or cathode and an additional lead for each color. Others, however, have only two leads positive and negative and have a built-in electronic control unit.
Decorative-multicolor LEDs incorporate several emitters of different colors supplied by only two lead-out wires. Colors are switched internally by varying the supply voltage. Alphanumeric LEDs are available in seven-segment , starburst , and dot-matrix format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Dot-matrix displays typically use 5x7 pixels per character.
Seven-segment LED displays were in widespread use in the s and s, but rising use of liquid crystal displays , with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.
In addition to power and ground, these provide connections for data-in, data-out, and sometimes a clock or strobe signal. These are connected in a daisy chain , with the data in of the first LED sourced by a microprocessor, which can control the brightness and color of each LED independently of the others. They are used where a combination of maximum control and minimum visible electronics are needed such as strings for Christmas and LED matrices.
Some even have refresh rates in the kHz range, allowing for basic video applications. These devices are also known by their part number WS being the most common or a brand name such as NeoPixel. An LED filament consists of multiple LED chips connected in series on a common longitudinal substrate that forms a thin rod reminiscent of a traditional incandescent filament. The filaments require a rather high voltage to light to nominal brightness, allowing them to work efficiently and simply with mains voltages.
Often a simple rectifier and capacitive current limiting are employed to create a low-cost replacement for a traditional light bulb without the complexity of the low voltage, high current converter that single die LEDs need. The current—voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage see Shockley diode equation.
This means that a small change in voltage can cause a large change in current. The typical solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Since most common power sources batteries, mains are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor.
However, the high resistance of three-volt coin cells combined with the high differential resistance of nitride-based LEDs makes it possible to power such an LED from such a coin cell without an external resistor. As with all diodes, current flows easily from p-type to n-type material. If the reverse voltage grows large enough to exceed the breakdown voltage , a large current flows and the LED may be damaged.
If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful noise diode. In general, laser safety regulations—and the "Class 1", "Class 2", etc. While LEDs have the advantage over fluorescent lamps that they do not contain mercury , they may contain other hazardous metals such as lead and arsenic.
Regarding the toxicity of LEDs when treated as waste, a study published in stated: In a statement of the American Medical Association AMA concerning the possible influence of blueish street lighting on the sleep-wake cycle of city-dwellers led to some controversy. So far high-pressure sodium lamps HPS with an orange light spectrum were the most efficient light sources commonly used in street-lighting.
These are even more efficient and mostly emit blue-rich light with a higher correlated color temperature CCT. Since light with a high CCT resembles daylight it is thought that this might have an effect on the normal circadian physiology by suppressing melatonin production in the human body. There have been no relevant studies as yet and critics claim exposure levels are not high enough to have a noticeable effect. The low energy consumption , low maintenance and small size of LEDs has led to uses as status indicators and displays on a variety of equipment and installations.
Large-area LED displays are used as stadium displays, dynamic decorative displays, and dynamic message signs on freeways. Thin, lightweight message displays are used at airports and railway stations, and as destination displays for trains, buses, trams, and ferries.
One-color light is well suited for traffic lights and signals, exit signs , emergency vehicle lighting , ships' navigation lights or lanterns chromacity and luminance standards being set under the Convention on the International Regulations for Preventing Collisions at Sea , Annex I and the CIE and LED-based Christmas lights.
In cold climates, LED traffic lights may remain snow-covered. Because of their long life, fast switching times, and visibility in broad daylight due to their high output and focus, LEDs have been used in brake lights for cars' high-mounted brake lights , trucks, and buses, and in turn signals for some time. However, many vehicles now use LEDs for their rear light clusters.
The use in brakes improves safety, due to a great reduction in the time needed to light fully, or faster rise time, up to 0. This gives drivers behind more time to react. In a dual intensity circuit rear markers and brakes if the LEDs are not pulsed at a fast enough frequency, they can create a phantom array , where ghost images of the LED appear if the eyes quickly scan across the array.
White LED headlamps are beginning to appear. Using LEDs has styling advantages because LEDs can form much thinner lights than incandescent lamps with parabolic reflectors. Due to the relative cheapness of low output LEDs, they are also used in many temporary uses such as glowsticks , throwies , and the photonic textile Lumalive.
With the development of high-efficiency and high-power LEDs, it has become possible to use LEDs in lighting and illumination. The Philips Lighting North America LED bulb won the first competition on August 3, , after successfully completing 18 months of intensive field, lab, and product testing. LEDs are used as street lights and in other architectural lighting.
The mechanical robustness and long lifetime are used in automotive lighting on cars, motorcycles, and bicycle lights. LED light emission may be efficiently controlled by using nonimaging optics principles. LED street lights are employed on poles and in parking garages. In , the Italian village of Torraca was the first place to convert its entire illumination system to LEDs.
LEDs are used in aviation lighting. LEDs are also being used now in airport and heliport lighting. LED airport fixtures currently include medium-intensity runway lights, runway centerline lights, taxiway centerline and edge lights, guidance signs, and obstruction lighting.
The lack of IR or heat radiation makes LEDs ideal for stage lights using banks of RGB LEDs that can easily change color and decrease heating from traditional stage lighting, as well as medical lighting where IR-radiation can be harmful. In energy conservation, the lower heat output of LEDs also means air conditioning cooling systems have less heat in need of disposal. LEDs are small, durable and need little power, so they are used in handheld devices such as flashlights.
This is especially useful in cameras on mobile phones , where space is at a premium and bulky voltage-raising circuitry is undesirable. LEDs are used for infrared illumination in night vision uses including security cameras. A ring of LEDs around a video camera , aimed forward into a retroreflective background , allows chroma keying in video productions.
LEDs are used in mining operations , as cap lamps to provide light for miners. Research has been done to improve LEDs for mining, to reduce glare and to increase illumination, reducing risk of injury to the miners. LEDs are now used commonly in all market areas from commercial to home use: LEDs are increasingly finding uses in medical and educational applications, for example as mood enhancement,  and new technologies such as AmBX , exploiting LED versatility.
Light can be used to transmit data and analog signals. For example, lighting white LEDs can be used in systems assisting people to navigate in closed spaces while searching necessary rooms or objects. Assistive listening devices in many theaters and similar spaces use arrays of infrared LEDs to send sound to listeners' receivers.
Light-emitting diodes as well as semiconductor lasers are used to send data over many types of fiber optic cable, from digital audio over TOSLINK cables to the very high bandwidth fiber links that form the Internet backbone.
Take note — there's a good chance that your return bus stop is located right across the street. As the bus approaches, check the electronic sign above the windshield to make sure this is indeed the bus you want. Wait for the bus to come to a full stop. The doors will open and you can hop on! If you need to change buses to get to your final destination, ask the driver for a transfer slip, which will get you on your next bus.
RTD offers a variety of pass programs, saving you money off regular cash fares. By purchasing passes or ticket books in advance, you won't have to worry about having exact change every time you ride the bus. Now that you're on the bus, sit back and relax!
The driver will announce stops over the loudspeaker, so wait until you hear yours. You may need to pull the "Stop Requested" cord above your head to let the driver know you want to get off. Exit the bus through the rear door if the bus has two doors. Always wait for the bus to leave before you cross the street, and never walk in front of the bus. And you can call the RTD Customer Care line for light rail info, too — they're happy to help! Next, head to the station. They're easy to find thanks to their open design, art work and red and white signs on nearby streets leading to the stations.
Now we are talking even lower power consumption for a comparable light output and those watt consumption numbers continue to go down. That is a stable measurement of light output that will not vary as LED light bulbs continue to get brighter and more efficient. Lumens per watt is even more important. How much light output are you getting from a product and how many energy dollars watts paid for on your electric bill do you need to spend to get that light output?
So here are some numbers for you to keep in mind when shopping for LED light bulbs. It won't be long before referencing incandescent bulbs is totally a thing of the past, so learn your lumen numbers now.
The higher the number, the brighter the bulb. For those of you who want to delve into the definition of lumens in a more detailed, technical manor, here is an article written for us some time ago by a professor, Robert Doc Bryant.
It's entertaining while still very informative. Get a birthday cake candle. Stick the candle on one end of the ruler. Turn out the lights. Sing Happy Birthday to Doc.
It was his 47th on the 23rd. Enough of that nonsense. One foot-candle of light is the amount of light that birthday cake candle generates one foot away. That's a neat unit of measurement. Say you have a lamp. You are told it produces foot candles of light. That means at one foot from the lamp, you will receive foot candles of light.
But here's where it gets tricky. The further away you move the light from what you want to illuminate, the less bright the light seems! If you measure it at the light, it's just as bright. But when you measure at the object you want illuminated, there is less light! That's a very scientific and math rich way of saying, the closer you are to the light bulb, the brighter that bulb is. Or, think of it this way. You can't change how much light comes out of your light bulb.
So, to make more light on an object, you have to either move the light closer, or add more lights. So, if we take your candle and ruler, lets place a book at the opposite end from the candle. We'd have a bit of a light up if we put the book right next to the candle, you know. If that book happens to be one foot by one foot, it's one square foot.
OK, got the math done there. Now, all the light falling on that book, one foot away from your candle equals both……. Ahh, we've confused you. Illuminance is the intensity or degree to which something is illuminated and is therefore not the amount of light produced by the light source.
This is measured in foot-candles again! And when people talk about LUX, it's illuminance measured in metric units rather than English units of measure. To reinforce that, LUX is the measurement of actual light available at a given distance. A lux equals one lumen incident per square meter of illuminated surface area. They're measuring the same thing, just using different measurement units.
Pretend you're an old photographer, like O.