The difference between main optical names of LED

The difference between main optical names of LED

LED luminaires are this kind of device which can transmit, distribute, and change the light distribution of light source. They are becoming the main products of a new generation of lighting market with its high efficiency, energy saving, safety, long service life, compact, and other technical characteristics. They effectively promote energy-saving environmental protection industry of high-speed development. The usual parameters of light which associate with photometry are light intensity, luminous flux, illuminance and brightness. Although these four quantities are related, they are different and can not be confused. Just as the physical quantity like pressure, gravity, pressure, quality, they represent different parameters and effects.

1. Light Intensity( I, Intensity)
Unit Candela (CD), this is the inherent properties of point source. It is to represent the convergence ability of light.
Definition: The luminous flux which light source emits to the unit solid angle in fixed direction is defined as light intensity.

Explanation: The light intensity is in terms of the point source, or the size of the light emitting body is relatively small when compared with the irradiation distance. This quantity is to show the convergence ability of the emitter in space. Light intensity represents the radiation capability of light in different directions, also popular to say that the intensity of the light is the degree of the intensity emitted by the light source. It can be said that the light intensity is the description of how "bright" the light source is, because it is a common description of the optical power and convergence capability. Light intensity is higher, light will looks more bright, and under the same conditions, the being lighted object will be more bright. Therefore, in the earlier time, people often use the this parameter to describe flashlight. The common mistake is that people often use the intensity to express the "brightness ". The "Brightness" which we talked above all be added with quotation marks, because this is our conventional brightness, not photometry strict sense of brightness in photometry. We will have a detailed description for the brightness.

2. Luminous Flux(F, Flux), the unit is lumen, that is lm.
It is the inherent attribute of the light source, and the total energy of the light source in the unit time, namely the light power
Definition: the amount of source emitted light in the unit of time is called luminous flux of the light source

Explanation: similarly, this quantity is in terms of the light source to describe the size of the total amount of light source, and is equivalent to light power. Higher the Light flux is, more light will be emitted. Compared with the mechanical unit, luminous flux is equivalent to the force, and the intensity is equivalent to pressure. To make the irradiated point looks more bright, we should not only improve the luminous flux, and also need to increase the convergence, actually is to reduce the area, so as to get greater strength. As we may know the luminous flux is also the artificial quantity. So it is not completely natural for other animals because this definition is completely based on the response of the human eye.

3. Light effect, unit is LM / W, that is how much luminous flux can be converted with 1w power.
As for the luminous efficiency of electric light source is another related topic, that's how much luminous flux can be transformed in the end with 1W power.The human eye responses differently to light of different colors, this feeling determines the conversion relationship between luminous flux and light power. Because human eye is most sensitive to the 555nm light, if half of the light converted to 555 nm light, and the other half turn into heat loss, then the efficiency is per watt 34.15 lumens. For the other colors of light, such as red light with 650nm, 1W power is equivalent to only 73 lumens. This is because the human eye is not sensitive to red light. For white light, that's depends. Because there is a lot of different spectral structure of white light. For example, there is large difference between LED white light and white light on the TV. The incandescent lamp is even hard to reach 1W=20lm, and the rest light are all turned to heat or infrared. That's due to the different spectrum.

4. Light Illuminance (E, Illuminance), unit is LX (formerly known as lux). To reflect the light shines or not from another point of view.
Definition: the light illuminance generated when 1 lumen evenly distributed on the surface of 1 square meter.

Explanation: Light illuminance is in terms of the lighted location, but it has nothing to do with the been lighted object. A luminous light, uniformly gives light to an object wiht 1.2m long, then the illuminance is 1 lx. People can use the illuminance photometer to measure the illuminance. In order to protect eye and make life and work convenient. The illuminance has different provision in different places. In fact, the illumination is the most easy parameter to measure(compared with other parameters), the illumination can also been tested by the integrating sphere.

5. Brightness (L, Luminance), unit is nits, namely nt. It reflects the light bright or not when the emitting surface or the reflection of light into the human eye.
Definition: the unit area of the light source in the normal direction, the light flow within the unit solid angle, which also called the light intensity of the unit area light emitting surface, that's candela / square meter.

Explanation: This is the most confused conception that can be easily understood. The brightness is in terms of light source not to the point source. In addition, the brightness of the light emitting surface is independent of the distance, but is related to the direction of the observer. Many people are confused about the concept of illuminance and luminance, actually the amount of total incident light in a unit area on the surface can be described as illumination; if illustrate the reflective total light in a unit area of surface from human eyes, then it can defined as brightness.

The usual test for luminaire are intensity, light effect, brightness and illuminance, these parameters are also the general requirements of laboratory. According to the LM-79, clause 9.3.1, there are only two kinds of goniophomter can be acknowledged. Namely, central rotating mirror type goniophotometer and circular motion reflecting mirror type goniophotometer. They are all the rotating mirror vertical distribution system which can automatically test 3D light intensity distribution curve. They can realize C-γ、A-α and B-β measurement solution and fully meet the CIE, IESNA, GB and many other international standards and in accordance with the LM-79 clause 9.3.1.

Usually engineer need use Integrating Sphere to test a lighting luminaire. The integrating sphere is used to provide a testing environment which can let the light evenly distributed. Lisun provide different diameter integrating sphere work with spectroradiometer to apply in measuring all kinds of lamp testing. The CIE-127-1997 and IES LM 79-08 suggest using the array-typed spectroradiometer and integrating sphere to test solid-state lighting products(SSL). The LMS-9000A combined the LED optical maintenance test function which is meet LM-80.

How to Solve the Stroboscopic Problem of LED Lighting?

How to Solve the Stroboscopic Problem of LED Lighting?

“Bright blind” in life is an exaggerated description of some impact incidents, but if it is used for the LED lighting industry, then it is the quality problems of LED lamp itself. And "strobe" is likely the initiator to lead to "blind". Many people are not very clear about the concept of strobe, and even don’t care about its harm. Regarding the hazard of strobe, experts have given the conclusion.

A lot of LED lights on the market use the pulse power supply, their cost is relatively cheap, at the same time conducive to adjust the brightness, and also extend the working life of lamp. However, it is not a continuous light, but flicker in a very high speed, we can not see with naked eye. Only our brain and retina can detect the strobe. This kind of flicker may cause headaches, decreased attention and vision loss.

Energy Bureau staff told the media that the government should exert more attention to this problem, improve the laws and regulations, so that make unqualified products disappear from the market. At the same time, he stressed that the LED energy saving light technology will be better and better. Compared with the old light bulb, the consumption of LED lamp is only its 1/10, so this act may also plays an active significance to energy saving.

For there is strobe or not, users can use a simple method to distinguish. Firstly, turn on the light and then open mobile phone camera function, put the camera lens at a distance of 20cm from the lamp, then observe whether there is a dark stripe flicker in the phone camera screen. If there is flicker, then this lamp has strobe, if there is no flicker, then you can use this lamp rest assured.

Dated 14th December, 2012, the EU officially released the (EU) NO 1194/2012 rules implementing rules of the European Parliament and the EU Council Directive 2009/125/EC on the eco-design requirements of directional lights, LED lights and related equipment requirements. Compared with  European Parliament and Council Directive 2005/32/EC implementing rules for non-directional household lamps eco-design requirements which posted by the European Commission Regulation (EC) NO 244/2009 Regulations dated 18th March, 2009, the new rules have complete mandatory and eco-design requirements.

For LED manufacturers, they can only use professional testing equipment to detect the stroboscopic problem of LED. The LSRF-1 Lamp Start, Run-up time and Flicker Test from Lisun Electronic (Shanghai) office is integrated equipment which can test Lamp Start, Run-up Time and Flicker. To meet EU ErP requirements, IEC60969 Self-ballasted Lamps for General Lighting Services Performance requirements and Energy Star about Lamp Start, Run-up Time and Flicker Test. LISUN developed ErP test system, the system hardware consists of PH3000 and LSP-500VAC; the software consists of LST-3000 Lamp Start and Run-up Time Test and FLK-3000 Lamp Flick Test.

 

Lisun Electronic (Shanghai) office is committed to the development and after-sales maintenance of lighting instrument, EMI / EMC test system and Electrical Safety Tester in the domestic and global market. The full range of products of Lisun are in strict accordance with the quality management and control of ISO9001:2008 requirements for R & D and production; Lisun is also the member of global lighting CIE association, all products are according to CIE requirements; in addition, all products of Lisun are certified by CE and get the qualification of the EU.

 

How to Solve the Stroboscopic Problem of LED Lighting?

“Bright blind” in life is an exaggerated description of some impact incidents, but if it is used for the LED lighting industry, then it is the quality problems of LED lamp itself. And "strobe" is likely the initiator to lead to "blind". Many people are not very clear about the concept of strobe, and even don’t care about its harm. Regarding the hazard of strobe, experts have given the conclusion.

A lot of LED lights on the market use the pulse power supply, their cost is relatively cheap, at the same time conducive to adjust the brightness, and also extend the working life of lamp. However, it is not a continuous light, but flicker in a very high speed, we can not see with naked eye. Only our brain and retina can detect the strobe. This kind of flicker may cause headaches, decreased attention and vision loss.

Energy Bureau staff told the media that the government should exert more attention to this problem, improve the laws and regulations, so that make unqualified products disappear from the market. At the same time, he stressed that the LED energy saving light technology will be better and better. Compared with the old light bulb, the consumption of LED lamp is only its 1/10, so this act may also plays an active significance to energy saving.

For there is strobe or not, users can use a simple method to distinguish. Firstly, turn on the light and then open mobile phone camera function, put the camera lens at a distance of 20cm from the lamp, then observe whether there is a dark stripe flicker in the phone camera screen. If there is flicker, then this lamp has strobe, if there is no flicker, then you can use this lamp rest assured.

Dated 14th December, 2012, the EU officially released the (EU) NO 1194/2012 rules implementing rules of the European Parliament and the EU Council Directive 2009/125/EC on the eco-design requirements of directional lights, LED lights and related equipment requirements. Compared with  European Parliament and Council Directive 2005/32/EC implementing rules for non-directional household lamps eco-design requirements which posted by the European Commission Regulation (EC) NO 244/2009 Regulations dated 18th March, 2009, the new rules have complete mandatory and eco-design requirements.

For LED manufacturers, they can only use professional testing equipment to detect the stroboscopic problem of LED. The LSRF-1 Lamp Start, Run-up time and Flicker Test instrument from Lisun Electronic (Shanghai) office is integrated equipment which can test Lamp Start, Run-up Time and Flicker. To meet EU ErP requirements, IEC60969 Self-ballasted Lamps for General Lighting Services Performance requirements and Energy Star about Lamp Start, Run-up Time and Flicker Test. LISUN developed ErP test system, the system hardware consists of PH3000 and LSP-500VAC; the software consists of LST-3000 Lamp Start and Run-up Time Test and FLK-3000 Lamp Flick Test.

 

Lisun Electronic (Shanghai) office is committed to the development and after-sales maintenance of lighting instrument, EMI / EMC test system and Electrical Safety Tester in the domestic and global market. The full range of products of Lisun are in strict accordance with the quality management and control of ISO9001:2008 requirements for R & D and production; Lisun is also the member of global lighting CIE association, all products are according to CIE requirements; in addition, all products of Lisun are certified by CE and get the qualification of the EU.

How to Test the Junction Temperature of LED?

How to Test the Junction Temperature of LED?

We know that the life of LED is closely related to its junction temperature. The key to prolonging its life is to reduce its junction temperature. And the key to reduce the junction temperature is to have a good heat sink that able to exhaust the heat generated by LED in time.

So, how to measure the junction temperature of LED?

Junction temperature seems to be a temperature measurement problem, but the junction temperature need to measure is in the internal of LED. Can’t we measure its temperature with a thermometer or a thermocouple into the PN junction. Of course, its shell temperature can be measured with thermocouple, and then its junction temperature can be calculated according to the thermal resistance Rjc (junction to the shell).

But things become more complicated after installing the radiator. Because usually LED is welded to the aluminum substrate, and the aluminum substrate is installed on the radiator. If you can only measure the temperature of the radiator shell, then it is necessary to know the value of a lot of thermal resistance to calculate the junction temperature.

Including Rjc (junction to case), Rcm (shell to the aluminum substrate, in fact, which also should include film printed version of the thermal resistance), Rms (aluminum substrate to the radiator), Rsa (heat sink to air), which only with one inaccurate data will affect the accuracy of the test. Figure 1 shows a schematic diagram of the LED to each thermal resistance of radiator. Where incorporates a lot of thermal resistance, making it more precision limited. That is to say, the accuracy of the junction temperature would be worse when inferred from the surface temperature of the radiator.

[caption id="attachment_10259" align="alignnone" width="800"] Figure-1-Schematic-diagram-of-LED-to-each-thermal-resistance-of-the-radiator[/caption]

Fortunately, there is an indirect method of measuring temperature that is to measure the voltage. Then the junction temperature is relative to which voltage? And what is the relationship?
Firstly, we should talk about the characteristics of LED volt-ampere.
We know that the LED is a semiconductor diode, which has a volt-ampere characteristic same as all diodes. The volt ampere characteristic has a temperature characteristic that is when the temperature raises, the volt ampere characteristic left shifts. The Figure. 2. shows temperature characteristics of the LED's volt ampere.

[caption id="attachment_10260" align="alignnone" width="800"] Figure-2-Temperature-characteristics-of-LED-volt-ampere[/caption]

Assuming that the LED is powered by a Io constant current, when the voltage is T1, the voltage is V1. While the junction temperature rises to T2, the entire volt ampere characteristic is left shifted, the current Io is constant, the voltage changes to V2. The two voltage difference is removed by temperature, then the temperature coefficient can be obtained and shown by mV/oC. For ordinary silicon diodes, the temperature coefficient is about -2mV/oC.

But the LED is not made of silicon material, so its temperature coefficient should also be measured additionally. Fortunately, most of the LED manufacturers give its temperature coefficient in the data table. Take XLamp7090XR-E high power LED for example, its temperature coefficient is -4mV/oC, and 2 times larger than the ordinary silicon diode. The volt ampere characteristic temperature coefficient of Luxeon Rebel from a company of USA is -2 - 4mV/oC. As for LED Puri array (BXRA) of the USA, it gives more detailed data.

[caption id="attachment_10263" align="alignnone" width="800"] Figure-3-Decay-curves-of-LuxeonK2[/caption]

However, the range of the data is too large, so that may loss the value of the using. Anyway, as long as the temperature coefficient of the LED is known, the LED junction temperature can be calculated from the forward voltage of the LED.

Lisun developed the T3 LED junction temperature thermal resistance electrical characteristic test, it can automatically record the changes of the parameters with time curve. Lisun Electronic (Shanghai) office is committed to the development and after-sales maintenance of lighting instrument, EMI / EMC testing system and safety testing instruments in the domestic and global market. The full range of products of Lisun are in strict accordance with the quality management and control of ISO9001:2008 requirements for R & D and production; Lisun is also the member unit of global lighting CIE association, all products are according to CIE requirements; in addition, all products of Lisun are certified by CE and get the qualification of the EU.

The LED Driver RMS Value Measurement and Analysis

As we known the quality of LED lighting products depend on two points: One is LED chip(light source); Second is LED power driver. In the practice, there only have few company can provide qualified LED chip such as PHILIPS, OSRAM and CREE in the market. Generally, the LED chip have very small change to get quality problem, but we heard many news about low quality LED lighting products was found and caused big losses to customers because of un-qualified LED driver. As considering the importance of LED driver, this article will discuss some technical introduction and measurement technology.

There have some necessary test items of LED Power Driver Tester  such as Crest Factor, Effective Power, Reactive Power, Apparent Power, Power Factor, Voltage/Current (RMS value, Average value) and THD harmonic parameters etc. In the practice measurement, lots of people found it have big difference between get from LED driver tester and multimeter, and this difference focus on Voltage/current rms, apparent power, power factor, RMS(rms) and average. Many users feedback the voltage/current(RMS date) from multimeter is lower or bigger than LED driver tester, it is necessary to make a explain here that the values from LED driver tester are RMS(true and effective value), the average curren we often talking is also RMS(average value), the average current only can get when it satrt test and it is RMS average value during start process; the software data is keep some with front panel of LED driver tester. In the meantime, according to international standards, the RMS(true and effective value) is needed only when test LED driver, it is meaningless to measure average value. The LED driver tester will show voltage, current and power, but the power is not equal of voltage multiply current; the voltage multiply current directly get inspecting power, the LED driver tester showed value is active power. If only use multimeter to measure average value, then there is no need use professional LED driver tester. According to IEC standard, the Voltage True RMS (Vrms), True RMS Current (rms), Active Power (P) and Power Factor (PF) calculate way as below:

In the above formula, “N” is stand the number of sampled points during the period (the period depends on the frequency of the signal to be measured) and the value at a certain sampling time. The LED driver tester provides two test methods to calculate the total harmonic distortion (THD), namely IEC and CSA, respectively:

In the above two formulas:

THD: Represents the relative value of voltage/current total harmonic distortion

C：Represents the K times harmonic effective value of the voltage or current

K：Number of harmonics

N：The maximum harmonic frequency (This LED driver tester is 50)

C：RMS value of fundamental voltage or current (ie, 1 harmonic)

In the practice measurement, when use RMS value or average value of LED constant output current to judge quality of LED driver, there have two ideas in the market: some use RMS value but some use average. Caused this two difference idea due to LED driver have big current ripple and each LED driver is different, then the RMS value and average value of output current have big difference, but according to the actual situation and standards, the only judge factor is focus on RMS value, we can refer average value but can't see it as key judge factor.

Color difference SDCM

Color difference SDCM

Color difference is an important indicator of CFL color performance. Color difference is the difference between computer calculation forma and the target standard, calculated by single lighting source, the value is smaller, accuracy is higher. Please note, it only represents the compared color of a light source, it can not detect the deviation under different light sources. Generally speaking, color difference refers to the distance that the measurement value deviates from the target value, the difference between the light source spectrum and the standard spectrum. It needs provide the target value and calculation formula to know the measurement value of color difference.

Standard spectrum changes with color temperature, the color difference is different for the same light source if the standard spectrum is different, but when test, general color photoelectric analysis system can automatically identify the color temperature range where the measured light source is, to determine the color temperature value of standard spectrum. When the color temperature is same, reference standard spectrum is consistent, chromaticity coordinate X,Y is different, the color difference is also different.

Color difference unit: SDCM. National standard has its specific testing requirement, GB-T17262-2002 single-ended fluorescent lamp performance requirements specified in the standard that general energy-saving lamps require color tolerance less than 5 SDCM. GB24823-2009 general lighting for LED modules performance requirements specified in the standard that LED modules require color difference less than 7SDCM. In the ellipse of 5SDCM, color difference is 5 if the point is on the curve of ellipse, color difference is less than 5 if the coordinates is in the circle of ellipse. IEC standard requires that the lamp chromaticity coordinate(x,y) should not deviate the rated value from 5SDCM, that is to say, the chromaticity coordinate of lamp should be in the ellipse, the color difference should be less than 5 SDCM for general energy-saving lamps. For color difference ellipse diagram, outer ring is 6SDCM corresponding to the national standard, inner ring is 5SDCM corresponding to international standard. Industry standard, Energy Star ANSI C78.376, Color Difference≤7SDCM; EU Standard IEC60081, Color Difference≤7SDCM; National Standard GB10682-2002, Color Difference≤5SDCM.

In the fluorescent lamp, as the density of red, green and blue powder is different, it is easy to cause color temperature difference in production. Once appear, it needs adjust color difference to adjust color temperature difference to ensure light color of light. White LED as light source, it should refer to color difference standard requirement to guide the development and application of white LED new lighting source. Lisun pushes LPCE-2(LMS-9000A) integrating sphere & spectroradiometer system and CHROMA-2 Pocket Chroma Meter to test color difference.

[caption id="attachment_10225" align="alignnone" width="800"] Color difference SDCM-1[/caption]

[caption id="attachment_10226" align="alignnone" width="800"] Color difference SDCM-2[/caption]

Lisun Group’s LPCE-2(LMS-9000A) integrating sphere & spectroradiometer system and CHROMA-2 Pocket Chroma Meter are widely applied to Luminaries manufacturing enterprise and lab, such as Sharp Electronics in Memphis TN(USA), PT. SHARP SEMICONDUCTOR INDONESIA (Indonesia), TUV Rheinland InterCert Kft.( Hungary), Philips Lighting(Netherlands), Sony Semiconductor Corporation etc. The reason why Lisun can win some many customers is because we always practice the motto of right products, right price and right service. Lisun will continue feedback good quality products and superior service in the feature.

Color difference SDCM

Color difference SDCM 

Color difference is an important indicator of CFL color performance. Color difference is the difference between computer calculation forma and the target standard, calculated by single lighting source, the value is smaller, accuracy is higher. Please note, it only represents the compared color of a light source, it can not detect the deviation under different light sources. Generally speaking, color difference refers to the distance that the measurement value deviates from the target value, the difference between the light source spectrum and the standard spectrum. It needs provide the target value and calculation formula to know the measurement value of color difference.

Standard spectrum changes with color temperature, the color difference is different for the same light source if the standard spectrum is different, but when test, general color photoelectric analysis system can automatically identify the color temperature range where the measured light source is, to determine the color temperature value of standard spectrum. When the color temperature is same, reference standard spectrum is consistent, chromaticity coordinate X,Y is different, the color difference is also different.

Color difference unit: SDCM. National standard has its specific testing requirement, GB-T17262-2002 single-ended fluorescent lamp performance requirements specified in the standard that general energy-saving lamps require color tolerance less than 5 SDCM. GB24823-2009 general lighting for LED modules performance requirements specified in the standard that LED modules require color difference less than 7SDCM. In the ellipse of 5SDCM, color difference is 5 if the point is on the curve of ellipse, color difference is less than 5 if the coordinates is in the circle of ellipse. IEC standard requires that the lamp chromaticity coordinate(x,y) should not deviate the rated value from 5SDCM, that is to say, the chromaticity coordinate of lamp should be in the ellipse, the color difference should be less than 5 SDCM for general energy-saving lamps. For color difference ellipse diagram, outer ring is 6SDCM corresponding to the national standard, inner ring is 5SDCM corresponding to international standard. Industry standard, Energy Star ANSI C78.376, Color Difference≤7SDCM; EU Standard IEC60081, Color Difference≤7SDCM; National Standard GB10682-2002, Color Difference≤5SDCM.

In the fluorescent lamp, as the density of red, green and blue powder is different, it is easy to cause color temperature difference in production. Once appear, it needs adjust color difference to adjust color temperature difference to ensure light color of light. White LED as light source, it should refer to color difference standard requirement to guide the development and application of white LED new lighting source. Lisun pushes LPCE-2(LMS-9000A) integrating sphere & spectroradiometer system and CHROMA-2 Pocket Chroma Meter to test color difference.

[caption id="attachment_10225" align="alignnone" width="800"] Color difference SDCM-1[/caption]

[caption id="attachment_10226" align="alignnone" width="800"] Color difference SDCM-2[/caption]

Lisun Group’s LPCE-2(LMS-9000A) integrating sphere & spectroradiometer system and CHROMA-2 Pocket Chroma Meter are widely applied to Luminaries manufacturing enterprise and lab, such as Sharp Electronics in Memphis TN(USA), PT. SHARP SEMICONDUCTOR INDONESIA (Indonesia), TUV Rheinland InterCert Kft.( Hungary), Philips Lighting(Netherlands), Sony Semiconductor Corporation etc. The reason why Lisun can win some many customers is because we always practice the motto of right products, right price and right service. Lisun will continue feedback good quality products and superior service in the feature.