日期：2012年5月10日

British towns staged a “midnight lights-off projects” to pursue led spotlights dimmable

“Midnight lights-off method” is swing in the all England rural, suburban and downtown street. Although some residents and police are worried about that it will increase the number of traffic accidents and crime. On the survey of 133 local goverment, 98 people said they are reducing the lighting of G24 LED Light, and some are intented to do so.

The county or even councial who participated in the survey, as well as several major cities, show that they are reducing the LED Tunnel Lighting or have this intention. Including Cardiff, Sheffield, Edinburgh and London in some areas.

On the contrary, Most small councils have no such plan. Some of which are only responsible for the lighting of the outside road region, such as parks, parking lots, and sidewalks.

Reducing street lighting projects includes cutting down some lighting, and installing new lights which can let led spotlights dimmable or close at the mid-lights such as LED Street Light. In some projects, we can through the new device to let processor make the lights dimmer or brighter.

A British parliament claimed that “Midnight lights-off method” can not only save electric charge, but also energy saving. The 7500 thousand street lights on British spent 5 million pounds annual year.

Right now,  Norfolk is currently being implemented one of the largest programs. Norfolk’s 3300 streets and rural areas will be taken to “Midnight lights-off ” starting from midnight to 5:00 to turn off the lighting system.

In addition, the main traffic lines will install more than 5000 led spotlights dimmable lights. The illumination intensity is reduced by 1/3, from 20:00 to 5:00.

The British Conservative Party Council said, the move can save £ 167,000 every year, but the Norwich Green Party MP Steven Altman citilized such projects.

He said: “The environmental and economic benefits of this program has been exaggerated. A lot of residents are worried that this approach will bring increased crime, and  expressed their opposition.

South Korea to promote high efficiency led lighting,fusion technology development $270 million of LED industry

The South Korean government announced in 2015, will invest 3,000 billion Korean won (about $ 279 million) to support the research and development of light-emitting diode (LED Lights). Korea Ministry of Knowledge Economy said in a meeting of economic policy adjustment. In order to push the high efficiency led lighting integration and technology development of the LED, the budget support of the total amount of 3,000 billion Korean won will be allocated  in the next five years, and to prepare ,and prepare promotion the LED industry to leap forward support strategy.

Known to promote the  original core technology development and popularization of LED High Bay lighting in public institutions by the Ministry of focus investment
in the early 2009. A new policy is focused on how to merge the LED technology with existing industries innovatively such as lighting, medical, and other integration and create a more high value-added technology.

The South Korean government put forward that ensure the new market-driven competitiveness and the market creation and consumer reliability, constitute the three major policy task in a industrial ecology of virtuous cycle, the plan to promote high efficiency led lighting integration career to the world’s advanced position before 2015.

Knowledge Economy Ministry combine the LED with IT first, will ensure lighting system that is  by individual or central control energy conservation , with tailored lighting of users
psychologically and physically , sterilization and purification function lighting etc new markets competitiveness.

The South Korean government invest 3,000 billion won within 5 years.Separated from the original blue LED,from the diversification of the particular wavelength or full color products , and preparations for the activated LED Plant Factory, the intelligent car headlamp innovative LED industrial base of integration.The South Korean government is also planning to implement rules marked of lighting functions and system of Management evaluation results etc in 2011.

Convenient for consumers to identify products. Also induce a large, small and medium enterprises to strengthen cooperation , also plan to manage high efficiency led lighting Forum in 2011 and provide of the LED Experience Exhibition of  technical exchanges between enterprises ,so that can reduce the cost burden of SMEs in the LED lighting certification, structure for a virtuous cycle of industrial ecology   .

South Korean government will organize a organization that the tentative name is LED policy agreement ” to help Smooth cooperation of enterprises and develop LED fusion technology . Additionally plan to let 70% building of Sejong City adopt LED lighting. Make the Sejong City mold into the LED Street Lights city ,to invest 10 billion won (about $ 9.29 million )  in 2011 , 60% ​and scope lighting of the river, 16 reservoirs will be replaced of high efficiency led lighting .

Industry policy officials of Information and Communication Ministry, the Liu Xiugen said that if integrate the force of the government and industry ,in the market of LED lighting and the integration markets formally opened within 1 to 2 years  , Korea will be able to ensure the dominant position .

Tasters of LED current

Why constant current is required?

Lighting Emitting Diodes need to work in strict working conditions. This is determined by their properties. LED Lights are vulnerable to temperature change. LED voltage will be changed along with temperature, consequently leading to the change of LED current. As we all know, each LED has a particular working current. Long-term working in a current larger than the working current will cause damages to LEDs, even destroy them. Here constant current means LED current will remain a constant value when external conditions change, like the increase of temperature and LED voltage. However, maintaining a constant current is not an easy job.

 

Lighting Emitting Diodes need to work in strict working conditions. This is determined by their properties. LEDs are vulnerable to temperature change.

 

How LED power suppliers match with LED light broad?

Some customers prefer to buy LED light broads at first, then look for power suppliers. It is very hard for them to find suitable suppliers (either with an excessive current and an insufficient voltage, like I>350mA,V<40V or with an insufficient current and an excessive voltage, like I<40mA,V>180V). This mismatching between LED High Bay Light broads and LED power suppliers will cause excessive working temperatures, low light efficiencies, or insufficient input voltages. The best way is to choose LED components from one LED manufacturer. Generally, LED light broads and LED power suppliers from one manufacturer are well matched. LED chips will be installed onto the light broad in a most suitable way that makes their designed suppliers play the best performance. If customers insist to use their own light broads, the best way is to let LED manufacturers design the particular power suppliers for them.

 

What is the suitable working current for LED?

Theoretically, LED working current is 20mA. Some manufactures set their LED current (the current pass though LEDs during their work) as 20mA, leaving no margin. It is improper to do so. In fact, LEDs will generate a large amount of heat under a current of 20mA. Even if we can keep the entire circuit to provide a constant current, it still can cause damages on LEDs, reducing their working lives. After many tests and comparisons, technicians have proved that the best working current for LED is 17mA.

 

What is the most suitable voltage for LED Grow Lights?

Normally, LED working voltage is around 3.0V-3.5V, most of them are 3.125V.

Small LED manufacturers brings chaos to LED lighting market

With the rapid development of LED lighting industry, the competition becomes more and more fierce. Almost every day, there will be a new born small LED manufacturers take part into this stream, especially in indoor LED lighting market. LED lamps are electronic products. They need particular constructions and covers just like traditional lamps, and also require LED lighting sources (all kinds of LEDs connected in series or in parallel), AD/CD constant current diver, cooling fins made by aluminium or ceramics. Traditional lamps are just electrical products. The main job for traditional lamp manufacturers is design the construction of lamp shape. Lighting sources: bulbs, are usually produced by specific factories. Compare to traditional lamps, the manufacturing technique of LED lamps is much more sophisticated. LED company and LED manufacturers need to employ designers and engineers from electronic, photonic and construction area, as well as common workers.

 

With the rapid development of LED lighting industry, the competition becomes more and more fierce.

 

Since LED lighting market is an emerging market, there is no identical standard established in this field. This leads to a chaos in LED lighting market. Especially for those who just transformed from traditional lamp manufacturers to LED lamp manufacturers, or new comers. In order to reduce risks and the cost of production, they have to purchase LED broads, AC/DC constant current drivers and cooling fins from other manufacturers, then combined these components together to get their final products. Most small LED manufacturers continuous to use their old method: buy a bulb and a cover, then assemble them. It is really an easy way, but only suitable for traditional lamps not LED lamps. However, it is not to say that LED high bay lights cannot be produced in this way. In the matter fact, this clumsy and feckless manufacturing method has been widely accepted within those new-born small LED manufacturers. They do not have their own tech patents. They do not have their own technologies. They omit a lot of necessary tests. They have no certificates. They are actually LED processing factories rather than LED manufacturers. In order to attract more customers, they must reduce products prices. This malicious competition will finally give birth to the disorder of entire LED lighting market. Products from these small LED factories are usually unqualified. Most of them are probably failed during the work. Some even have potential safety hazards.

 

Analysis for light intensity of Light Emitting Diode

There three units can be used to present light intensity: Lux (unit of illuminance: the illuminace of 1L light within one cubic centimeter), Lumen (unit of illuminous flux: the illuminous flux of 1CD light within one square centimeter) and CD (unit of LED Street Light intensity: the light intensity of a fully radiated matter (bellow the platinum freezing point) per 1/60 centimeters).

 

The compact installation of several LEDs together will lead to the superposition of spherical lights of them.

 

Usually, CD is used to represent light properties of light sources like, filament lamps, LED lamps. Lumen is typically used to represent light properties of reflectors or objects with penetrability, like CD projectors. Lux is used in the photographic area. In fact, these three units are equivalent numerically, but need to be interpret from different perspectives.

 

In practical, light intensity is usually represented by units or transformed units that can be easily surveyed and mapped. LED displayers always use CD/cm2 as light intensity unit, together with observing angle. Generally, outdoor LED displayers require a light intensity higher than 4000CD/cm2 to gain an ideal display effect. While indoor LED displayers usually require a maximum light intensity between 700 CD/cm2 and 2000 CD/cm2.

 

The light intensity of single Light Emitting Diode can be represented by CD, together with observing angle. Light intensity has nothing to do with light color. Normally, the light intensity of single LED range from several mCD to 5000 mCD. The light intensities given by LED manufacturers are measuring values in particular conditions: under 20 mA working current, observed in best visual angle, the most bright point in central. The beam angle and intensity distribution are determined by the form and position of lens mounted on the top of LEDs. Generally speaking, Light Emitting Diode with a small beam angle will send out brighter (higher light intensity) lights.

 

The compact installation of several LEDs together will lead to the superposition of spherical lights of them. However, the entire spherical intensity is evenly distributed. We call it average spherical luminous intensity (MSCP). When we measure MSCP, we need to take LED visual angle and the number of LED down lights into account. And multiple the maximum spot light intensity (given by product specifications) with 30%-90% (depends on the packaging), then we can calculate the approximate light intensity of single Light Emitting Diode.

How Light Emitting Diode send out lights with different colors

Light Emitting Diode (LED) is a type of electronic components that convert electric energy into optical energy. Most LED Projects can send out lights within the range of infrared rays and blue rays. At present, Light Emitting Diode sending out purple rays and even ultraviolet rays has been invented. Besides, LED manufacturers also made a kind of white LED by coating a layer of fluorescent powder on a blue-ray LED. In the next section, we will discuss more details about color manufacturing technique of LED Street Light.

 

Light Emitting Diode (LED) is a type of electronic components that convert electric energy into optical energy. Most LEDs can send out lights within the range of infrared rays and blue rays.

 

Light Emitting Diode made by different materials can emit photons with different energy. In other words, wavelength (color) of the light can be controlled by LED manufactures. In history, GaAs is the first materiel used to make LEDs. The minimal working voltage in forward bias is 1.424V. LEDs made by GaAs can only emit infrared rays. Another commonly used LED material is GaP. LEDs made by this material have a higher working potential: 2.261V, sending out green lights.

 

Based on these two types of materials, a new material construction GaAs1-xPx (x represents the ratio of phosphorus to arsenic) was used in the early LED industry. This new material construction realized multi-colored LEDs ranging from red rays to green rays. The wavelength (color) of the light is usually determined by the band gap (potential) PN junction, like red LED with a material construction of GaAs0.6P0.4, orange LED (GaAs0.35P0.65) and yellow LED (GaAs0.14P0.86). LEDs using material of arsenic, phosphorus and gallium were typically named “three elements LEDs”.  Blue LEDs (GaN), green LEDs (GaP) and infrared LEDs (GaAs) are named “two elements LEDs”. The latest manufacturing technology is combining Al, Ga, In and N together as AlGaInN. LEDs made by this new four-element-compound can send out lights ranging from infrared rays to ultraviolet rays.

 

Some people may ask: how can a Light Emitting Diode send out white rays? In fact, white is a combination of red (21%), green (69%) and blue (10%). However, due to the manufacturing technique, it is impossible for LED spot Lights to emit purely red/green/blue rays. Thus color matching is necessary. Workers need to combine three colors in proportion, and meanwhile control the light intensity of them respectively to create approximate white rays.

How to measure the temperature of LED PN junction? (2)

Some people suggest that the temperature span should be larger than 50 degrees when measure the PN junction temperature by using voltage method. The voltage-temperature relation will be linear in normal working temperature range of LED Lights, it is useless. The room temperature is 25 degree. According to the suggestion mentioned above, next measuring temperature be around 75 degree. However, the upper limit of the normal working temperature of LED PN junction is 70 degree. Is there any reason for us to measure the voltage-temperature factor in 75 degree: a cannot-be-reached temperature under normal use? It is impossible for a LED manufacturer to build a very sophisticated temperature-controlled lab. Thermostatic equipments can only keep the temperature within a range. It is also impossible to obtain accurate measuring results by using them.

 

Some people suggest that the temperature span should be larger than 50 degrees when measure the PN junction temperature by using voltage method.

 

However, if we are unable to fix the surrounding temperature, we can obtain accurate voltage-temperature factors through the relative temperature derivative, and consequently working temperature of LED PN junction. Firstly, we need to record the room temperature, namely the pre-working PN junction temperature. This temperature can be treated as the initial junction temperature corresponding to the initial voltage. Secondly, apply a voltage on both sides of LED Products, wait until the entire PN junction working in a stable condition, then read the voltage value. In accordance with measured voltage and the predefined voltage-temperature factor, we can calculate the increase value. Add this value together with the room temperature measured previously, then we have the final LED PN junction temperature, which is quite closed to the real value. Overall, voltage method is much more precise than thermal image method.

 

Formulas for thermal resistance method given as followed:

Rθ = (Tj-Tc)/P

Rθ is the thermal resistance of PN junction. Tc is the package temperature. P is the power consumption. Rθ andTc are fixed values given by the production specification. Once we know them, we can calculate the LED PN junction temperature Tj through this formula. There is another problem, how can LED chip manufacturers measure thermal resistances? They need to know junction temperature at first! In fact, this method is not used to calculate PN junction temperature. On the contrary, it is used to calculate thermal resistance though junction temperature. Most LED High Bay manufacturers still use voltage method to measure junction temperature.

How to measure the temperature of LED PN junction? (1)

More and more people realize that estimating the specific temperature of LED chips by measuring LED lamps covers temperature is inaccurate. However, how to get the exact temperature of LED PN junction? At present, there are three commonly used PN junction temperature measuring methods: thermal resistance method, voltage method and thermal imagine method.

 

More and more people realize that estimating the specific temperature of LED chips by measuring LED lamp covers temperature is inaccurate.

 

Thermal imagine method requires very expensive instruments which cannot be afforded by ordinary people. However, using thermal imagine method to measure PN junction temperature cannot guarantee the accuracy of results. Thermal imagines can only display the general heat distribution. There are many other things need to be taken into account to get the accurate temperature value. Surface emissivity is the main factor. In order to measure accurate temperatures though thermal image, we need to set a surface emissivity value at first. However, in the surface of LED Street Light chip, there are several materials. Different materials have different surface emissivity values. Even if every exact surface emissivity value was known by us, which one should be chosen as the reference value? Meanwhile, if we successfully obtain the accurate temperature by thermal images, it is a surface temperature, what about the temperature of LED PN junction? No matter what kind of optimization is taken, thermal imagine method can only get an approximate value. Therefore, it is a not commonly used method to measure temperatures of PN junctions. In the next step, we are going to do some introductions about thermal resistance method and voltage method.

 

Voltage method:

According to semiconductor theory, the voltage of PN junction is not only a function of temperature, but also a function of current. And the relation between junction voltage and junction current is not linear, which means voltage-temperature relations are different under in different current. Thus, if we intend to measure the temperature of LED PN junction, the working current needs to be known at first. Before measuring PN junction temperature using voltage method, we need to set a fixed constant working current for LED High Bay. Then put them into a thermostatic equipment to offer a constant working temperature. The last step is reading the measuring voltage value. Change into another temperature, repeat this operation once again. Normally, 3-5 measuring results can give out a relatively accurate relation between voltage and working temperature of LED PN junction, namely voltage-temperature factor.