视觉日记#12042015: Rush Surry Hill- 摇滚的汉堡店

坐落于城市的三岔路口,比邻纹身店,酒吧,和(曾经的)黑社会堂口,在这日复一日的车水马龙中,这家摇滚到爆的汉堡店,便孤芳自赏地张扬着一种独特的个性。
从店门前的招牌就可以得知,黑色和白色便是这个地方的主题。其背景的纹路,让人联想到压铸钢板上纹路,而这,也是许多重金属live舞台常用的冷酷和硬派。
带着悻悻然的心情进入到店内,只见大片黑色和白色将厨房和用餐区随意而鲜明地区分了开来。噢!天使与恶魔!善良(此处应有一脸坏笑)的我便自觉地把头向白色的那方望去,猛然发现,事情并没有这么简单。所谓的天使,其实是个满身纹身打满耳洞的朋克怪咖。无论是墙上鲜艳的涂鸦,还是那幅充满美漫风格的挂画,都像强烈的重低音一样向我的眼球侵袭过来。
忽然间,恶魔那边传来了浓厚的煎汉堡味,勾起了我隐约的喉咙痛。深邃的黑色墙面,锃亮的银色炊具,油腻煎板上吱吱作响的肉饼,这一切一切,都很有默契地出演着铁与火的激情。我想,如果哪一天我想寻求刺激,在这里享用一个汉堡会是一个不错的选择。不过在这个当下,还是出去呼吸一下新鲜空气吧。
IMG_4016 IMG_4017 IMG_4018 IMG_4019 IMG_4020

听觉日记#0102042015: 拉威尔 《镜:丑角的晨曲》

这是《镜》组曲的第四乐章,也是其中最著名的一首。变奏十分极端,演奏技巧相当困难,歌曲寓意尤其复杂。充分体现了这位音乐鬼才的恶趣味。
乐曲通过复杂的跳音,和明朗乐段到哀伤乐段的突然过渡,来描述小丑心中复杂的快乐与悲伤。乐曲一开始,小丑来到人群中,蹦蹦跳跳,大摇大摆,展示着那用各色颜料画成的大笑脸。随后,当小丑远离人群,强烈的悲伤和疲倦感忽然从心中翻滚起来,却又因为怕弄花了颜料,而死死忍住即将决堤的泪水。最后,确认四下无人,便不顾形象,竭斯底里,又哭又笑,泪奔而去。
其实我们又何尝不是那个小丑呢?每日在人前,我们都习惯戴上虚伪和防备的面孔,迎来送往。但当人群散去,只剩自己的时候,却是忧从中来,不可断绝。正如《金刚经》所言,所有悲苦,皆因着我相,人相,众生相,寿者相啊。
ravel 020202      revel 02 01

听觉日记#0101042015:拉威尔《镜:汪洋孤舟》

钢琴组曲《镜》,是法国古典乐界的浪漫主义者拉威尔,于晚年写给当时的年轻音乐家们的。《汪洋孤舟》是其中的第三乐章。
从乐曲的第一个音符开始,茫茫大海,无垠天空,便不由分说地展现在眼前。天很蓝,海很安静,一叶孤舟缓缓行驶于海天之间。
随后,随着变奏部分的开始,风暴突如其来!乌云笼罩天空,海面巨浪滔天!狂风呼呼呼地敲击桅杆,暴雨刷刷刷地拍打船身!隆!隆!隆!雷暴也汹涌而至!小船摇摇晃晃!小船孤立无援!
慢慢地,高潮部分过去,雨停了,海面安静了,随着乌云散去,天边开始出现一道道金色的光柱。最后,天恢复蔚蓝,海恢复平静,一叶孤舟缓缓行驶于海天之间。
Revel 01 01     Revel 02 02

视觉日记#0129032015:one central park(昼)

所谓小隐隐陵薮,大隐隐朝市。白昼的central park tower或许就是法国建筑逸才Jean Nouvel 对于“隐逸”的阐述。这是一方坐落于闹市中的灵山秀水。外墙的黑色和绿色,是被攀爬类植物巧妙撮合了的钢铁和玻璃,伟岸而柔和。信步进入建筑物的内部,车水马龙的喧闹戛然而止。大量生长于大堂的湿生蕨类植物,电梯一旁的大型反光面,和玻璃穹顶上透射着的水波粼粼,带来了只属于深山洞窟中的幽静和清凉。随着电动玻璃门的关闭,我这颗烦躁的心,便被隐藏在这一片洞天福地的闲适气氛中。

central park3central park1central park2

LED Flickering: A Devil hides under the Light

January 2015

Introduction

Invented by American Inventor Nick Holonyak Jr in 1962, Light Emitted Diode (LED), as commonly believed, is a completely new energy saving lighting technology with series of advantages, for example, a much lower energy consumption and a much longer lifespan. However, there are still shortcomings within LED products, while flickering is the most common one (Chen L and Zhan WX, 2014)[i] . Over the last few years, a large number of LED luminaires have been found to exhibit serious visual flickers. Especially for retrofit MR16 or GLS lamps, which can have various types of flickers, due to the poor compatibility of commercial and domestic dimmers. Graph 1 and 2 had illustrated the speed camera test results of two LEDs. It can be seen that the experiment downlight of Graph 1 had displayed a strong 100Hz flicker, which may be from an inadequate DC converter. In comparison, the luminaire of Graph 2 had exhibited no visible flicker. (Hammarb ck, 2013)[ii]

Typically, flickers of LED lights are in a high frequency flickering (>1000Hz). Although it is normally invisible ripple for most people, it can still trigger a series of ocular illness. That is why I call LED flicking a devil that hides under the bright light.

 IMG_3503  IMG_3502
Graph 1 Speed camera photo test for flickering LED downlight Graph 2 Speed camera test for non-flickering LED downlight

Problems

According to the research from Nantong University, China (2011), under flickering lights, pupils in human eyes needs to adjust frequently for the visualisation on the macula, this will likely cause eyestrain and myopia(Yu et.al., 2011)[iii].  Even worse, researchers from the State of Ohio University, USA claims that long term expose in low frequency flicker lights can cause severe vision-threatening diseases such as detachments, choroid atrophy, cataracts and glaucoma (Walline et. al., 2011) [iv].Besides, if the flickering is in a frequency as high as several kHz, human eyes cannot be able to adjust fast enough to adapt the variation of irradiance. Thus, the excessing amount of light spectrum from the Led light will damage the retina, and causing photomechanical damage (Chen L and Zhan WX, 2014)[v].

On the other hand, it is indicated by some other researches that the impact of flickering can be varied, as some people are naturally more sensitive to ripple of lights. Even for the same person, the flicker threshold and the critical flicker fusion can also varied in accordance of time of day, mood, stress, hormone levels, etc. (Wilkins,2010)[vi]. Nonetheless, against all the negative effects above, there is no doubt that LED flickering is not acceptable.

Solution

Frankly, there is no single solution for LED flickering. Although IEEE PAR1789 had initiated a series of measures for safe flicker levels from LED lights. Unfortunately, these works are still in progress, and some time will be taken for it to formalize into specific standards, and additional time is also needed for these new technologies to be commercialized. Thus, to tame this devil, there is still a long way to go (Hammarb ck, 2013)[vii].

However, as a consumer, it is not necessary to get headache by considering all of the technical issues, as there a simple measure to avoid LED flickering, which is to find out the flickering index of a certain LED luminaire. This data can be found on the website of LED Benchmark®, an independent testing laboratory for LEDs. Graph 3-1 and 3-2 had shown the result of flickering test for two different LED products. It is obvious that luminaire A has a lower flickering than luminaire B, as it is indicated by to the much lower value of flickering index and percentage.

 3-1  3-2
Graph 3-1 flickering test result of Luminaire A Graph 3-2 flickering test result of Luminaire B

(Source: LED Benchmark)

Summary

Even though we are not yet able to resolve LED flickering, we can still easily get away from this devil by paying more attention when choosing an LED product. So, next time when you are looking for an LED light, please keep an eye on its flicking data, instead of only looking at the prices.

Reference:

[i] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3949479/

[ii] Hammarb ck. P (2013), LEDs and Return of the Flickering, Lighting Magazine (October/November 2013), page 36-38

[iii] Yu Y, Chen H, Tuo J, Zhu Y. Effects of flickering light on refraction and changes in eye axial length of C57BL/6 mice. Ophthalmic Res. 2011;46(2):80–87

[iv] Walline JJ, Lindsley K, Vedula SS, Cotter SA, Mutti DO, Twelker JD. Interventions to slow progression of myopia in children. Cochrane Database Syst Rev. 2011;7(12):CD004916

[v] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3949479/

[vi] Wilkins,A (2010) LED Lighting Flicker and Potential Health Concerns:IEEE Standerd PAR1789 Update. Energy Conversion Congress and Exposition (ECCE),2010 IEEE, pp 171-176

[vii] Hammarb ck. P (2013), LEDs and Return of the Flickering, Lighting Magazine (October/November 2013), page 39

(Cited from IYL2015 blog) Rainbows, when the light becomes poetry

Rainbows, when the light becomes poetry

First and Second order Circular Rainbow in Nyalam, Tibet 2014. Credits: Antigone Marino

This summer I was traveling in Tibet. It was a hot day, and we were moving from the Tibetan Plateau down to the Kathmandu Valley in Nepal, jumping fast from 5,000m to less than 1,500m altitude. We had a stop in the Nyalam, a small Tibetan town of the Shigatse Prefecture near the border, situated at 3,750 meters above sea level. When my sister, with an astonished voice asked me “What’s that up in the sky?”

I had not time to answer as I was already pointing up with my camera to catch the first and only circular rainbow I have ever seen. A few seconds after, with my face still hidden from the camera, I was trying to build up a possible, realistic and credible physical explanation of that phenomenon, not to lose the credit of “all you can answer” optician in front of my sister.

That’s something you have to face every day when you are a scientist: people can ask you whatever they want, whenever they want.

That episode reminded me of a previous one which happened in Norway in 2009. I was traveling with some friends when we saw a rainbow and its second order one. They felt so lucky to see two concentric rainbows, that I had no pluck to tell them that it was the same one!

First and Second order Rainbow in Norway, 2009. Credits: Antigone Marino

Both episodes showed me the polyhedric feelings triggered by the vision of a light phenomenon as common as rainbow. From Greek mythology, where Iris is the personification of the rainbow and a messenger linking the Gods to humanity, up to the LGBT movement, whose symbol is a rainbow flag to reflect the diversity of their community, rainbows have been always associated to creation, divinity, good luck, duality, peace, energy and even gates for extraterrestrials worlds. It has probably been one of your first drawings when you were a child. According to the developmental psychologist Jean Piaget, rainbow drawings are typical of the preschool years, when children are approaching realism, but drawings remain fanciful: as ground and sky that never meet at the horizon, or rainbows formed without a drop of rain, as if we want to preserve its magical colorful poetic image from the wet, dark and tedious rain.

By the way, although we have a poetic vision of rainbows, we cannot resist asking what they are. A rainbow is an optical phenomenon caused by interaction of light, normally the sun, with water droplets, normally after the rain. In general, when light passes from a medium to another one, it splits in two parts: one reflected and one refracted.  Let us imagine, now, that the first medium is the sky, and the second one is a water droplet. When the sunlight encounters a raindrop, part of it is reflected and another part is being refracted at the surface. When this light hits the back of the drop, once again reflection and refraction happen. And if we follow just the reflected light, it will be again reflected and refracted again when trying to escape the raindrop.

Interaction of light with a rain droplet. Credits:  Wikimedia Commons

Without entering into too much detail on the physics, the overall effect is that part of the incoming light is reflected back over the range of 0° to 42°, with the most intense light at 42°. This angle is independent of the size of the drop, but does depend on its refractive index. Like on the Pink Floyd cover of the album The Dark Side of The Moon, showing light dispersion in a prism, also in a raindrop the amount by which light is refracted depends upon its wavelength, and hence its color: blue light is refracted at a greater angle than red light, but due to the reflection of light rays from the back of the droplet, the blue light emerges from the droplet at a smaller angle to the original incident white light ray than the red light. That’s why you will always see blue on the inside of the arc of a rainbow, and red on the outside. If you are so lucky that raindrops are big enough, and light reflects twice inside them, you will see a secondary rainbow at an angle of 50–53°. In this case colors are inverted compared to the primary one, with blue on the outside and red on the inside.

For the moment, hoping not to have destroyed your love for rainbows, I just explained you why it is possible to see two concentric and inverted images of a rainbow, like in Norway. They are just the same phenomena, the same rainbow.

To answer to my sister the question about the circular one, we first have to understand why rainbows have an arch-shape. As brilliantly explained on Wikipedia, “rainbows can be seen depending on the particular observer’s viewpoint as droplets of light illuminated by the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer’s eye. This light is what constitutes the rainbow for that observer. The whole system composed by the sun’s rays, the observer’s head, and the spherical water drops has an axial symmetry around the axis through the observer’s head and parallel to the sun’s rays. This already explains the circular arc-shape of the rainbow: whatever is the effect of any water’s drop on the observer, rotating around the axis must leave it unchanged. Therefore, the bow appears to be centered on the shadow of the observer’s head, or more exactly at the antisolar point (which is below the horizon during the daytime, unless the observer is sufficiently far above the earth’s surface), and forms a circle at an angle of 40–42° to the line between the observer’s head and its shadow. As a result, if the sun is higher than 42°, then the rainbow is below the horizon and usually cannot be seen as there are not usually sufficient raindrops between the horizon and the ground, to contribute”.

Oops, I think that this means I have no answer for my sister, as one cannot see a circular rainbow if I don’t have the right vantage point.

Looking at the phenomena in Tibet, the first thing I noticed was that the color sequence was the reverse of the rainbow. But…can you say to someone skipping happily that it was not a circular rainbow?! Even if physicists have the responsibility to truthfully describe nature, they should preserve an undefined percent of poetry and illusion in people. That’s why I answered “a kind of rainbow”.

What we saw in Tibet was a halo created by reflection and refraction in hexagonal ice-crystals, instead of water drops. What happens close to the border between Nepal and Tibet is that the warm and wet air coming from the Nepalese subtropical valley goes up, reaching at the Nyalam altitude the cold Himalayan climate. In these conditions it is easy to have ice-crystals formation in the troposphere.

Rainbows and halos both rise from a refraction phenomena. The former between sunlight and water droplets, the latter between sunlight and ice-crystals. Halos can have different shapes (pillar, spots and arc), while rainbows appear as arches. In circular halos, the size is constant, determined by the angle of refraction through six-sided ice crystals. The primary halo is always 22°. If color is visible, it will be red on the inside and blue on the outside. The larger halo at 46° has reversed colors.

Even such scientific explanation does not overshadow the fashion of a sunlight ray transforming itself in a painter’s palette. And if I know what happens, I cannot hide the wonder and joy that I feel all the times that light show me all its colors.

Now that I have the answer for my sister, I start to think who’s next. Which friend will stay with me in front of a rainbow wearing polarizing sunglass? In the meantime, I’ll start to write my answer, hoping to share it with you another time.


CNR_A.MarinoAntigone Marino is researcher at the Institute for “Superconductors, oxides and other innovative materials and devices” of the Italian National Research Council. She received her master of science in Physics in 2000, and the research doctorate in New Technologies in 2004, both at the Physical Science Department of Federico II University of Naples, in Italy. Her research activities have been concentrated on the study of soft matter optics applied to telecommunication, with a special interest in liquid crystals technologies.

She works for several learned societies. Since 2013 she is chair of the Young Minds project from European Physical Society. The project, aimed to promote the next generation of physicists, includes nowadays more than 300 young scientists from over 27 Sections in 14 countries.

Brief explanation of Clipsal C-bus system and its compatibility with dimmable LED lights

Nowadays, the “C-bus ” control  has been used widely for the HVAC and Lighting controls within commercial and residential buildings. Beside the convenience and effectiveness it brought, C-bus had also become one of the greatest headache for most of the electricians. As a lighting person, I have frequently encountered questions about C-bus from my clients. Thus I think it is it is worthy to share what I know about C-bus, and its compatibility with dimmable LED lights.

What is C-Bus

The “C-bus” system is a micro-processor-based control and management system for commercial and residential building, and it is patterned and owned by Clipsal® Australia.Be ware, it is not a dimming protocol.

This system can be used to control lighting and a wide range of other electrical devices, such as motor, pump and audio visual devices. For lighting, in particular, it can be able to manage from a simple ON/OFF control for a lighting circuit, to as complex as dimming a particular light accompany with sensors[1]. For a better understanding, please refer to chart 1, which is the simple flow chart for a typical C-bus system:

 C-bus flow chat 2

Chart 1: C-bus network flow-chart

(For more information, please refer to the C-bus Training manuals[2]. Special thanks for Ian Booker from Clipsal® technical support).

 Is my dimmable LED compatible with C-bus?

To find out the answer of this question, in my experience, there are two other things that need to be clarified:

1.    How my LED light is be dimmed?

Without doubt, this is the first thing you have to know. In the Australian market, most of the LED lights are power by electronic drivers, which means that they can be dimmed by trailing edge or universal dimmers. While for retrofit LED fixtures (for example some of the LED MR16 light bulbs), leading edge dimmers can be suitable as well. Of course, there are still lots of other different types of dimmable LEDs, you can always find my previous article “How to choose a dimmable LED?” for more information. Anyway, please ask your lighting supplier if you are not sure about it.

2.     Is my C-bus system on a dimmer?

Although it seems like a foolish question, the fact is, the reason of some problems regarding to C-bus dimming, is the system is not even on a dimmer. Regarding to this problem, there are basically two ways to find out if there is a dimmer in the system:

To begin with the most straightforward way, according to Ian Booker from Clipsal® technical support, you can always install a normal halogen lamp onto one of your C-bus output terminal, and try to dim it via your control interface. If the lamp can be dimmed, it means that the system is on a dimmer, and the way to fix the problem is either changing the correct LED light, or to change your C-bus dimmer unit. Otherwise, if the light cannot be dimmed, then it is no doubt that the system is not on a dimmer.

Moreover, there is also a not-that-easy way, which is, check through the PC interface. As a control network, the entire C-bus system is controlled through the network bridge, and it can be programmed and inspected through the PC interface. All you need, is to connect it to a laptop with the “C-bus toolkit” software installed. This software is a free application that can be downloaded from the Clipsal technical support website[3]. Through this software, you can easily find out if a dimmer is installed within the system network. However, it is strongly advised that you should find a licensed technician to do this job for you, at an incorrect programming may exert potential risks.

3.   Is my dimmable LED matches my C-bus dimmer ?

OK, if you have a clear idea of the dimming protocol of your Led light, and sure that you C-bus system is on a dimmer, it is time to figure out if your LED and your system matches with each other. To sort this out, in my experience, you can find out the part number of your C-bus dimmer, and figure out what protocol it is under. Table 2-1 to 2-3 in the Appendix section illustrate the part number and the dimming protocol for all the conventional C-bus dimmers, hope it can be a reference while you checking your C-bus dimmer. They are:

  • Table 2-1 : High power dimmer
  • Table 2-2: Analogue dimmers (Din-Rail and 0-10V )
  • Table 2-3: Digital dimmers (DSI, DALI and DMX)

Summary

Frankly speaking, although C-bus system has sometimes given us a great amount of trouble, if you can spend some time on it, it will eventually become an effective tool that make your life more convenient and colourful.

Appendix:

Part number Name Dimming Protocol No. of Channel Current Rating
L5112D10UAR6 L5112D Range 12 channel Infinity Architectural Dimmer All dimming protocol 12 40A 3 phase
L5112D5UAR6 L5112D Range 12 channel Infinity Architectural Dimmer All dimming protocol 12 20A 3 phase
L5106D20UAR6 L5106D Range 6 Channel  Infinity Architectural Dimmers All dimming protocol 6 40 A, 3 Phase
L5106D16UAR6 L5106D Range 6 Channel  Infinity Architectural Dimmers All dimming protocol 6 32 A, 3 Phase
L5106D10UAR3 L5106D Range 6 Channel  Infinity Architectural Dimmers All dimming protocol 6 20 A, 3 Phase
L5106D5UAR3 L5106D Range 6 Channel  Infinity Architectural Dimmers All dimming protocol 6 10 A, 3 Phase
L5103D20UAR1 L5103D Range 3 Channel Infinity Architectural Dimmers All dimming protocol 3 20 A, 3 Phase
L5103D16UAR1 L5103D Range 3 Channel Infinity Architectural Dimmers All dimming protocol 3 16 A, 3 Phase
L5103D10UAR1 L5103D Range 3 Channel Infinity Architectural Dimmers All dimming protocol 3 10 A, 3 Phase
L5103D5UAR1 L5103D Range 3 Channel Infinity Architectural Dimmers All dimming protocol 3 5 A, 3 Phase
L5112D20LP L5112D Range 12 Channel Professional Dimmers All dimming protocol 12 60 A, 3 Phase
L5112D16LP L5112D Range 12 Channel Professional Dimmers All dimming protocol 12 60 A, 3 Phase
L5112D10LP L5112D Range 12 Channel Professional Dimmers All dimming protocol 12 40 A, 3 Phase
L5112D5LP L5112D Range 12 Channel Professional Dimmers All dimming protocol 12 20 A, 3 Phase
L5112D3LP L5112D Range 12 Channel Professional Dimmers All dimming protocol 12 36 A, 1 Phase; 18 A, 2 Phase
L5106D20LP L5106D Range 6 Channel Professional Dimmers All dimming protocol 6 40A 3 phase
L5106D10LP L5106D Range 6 Channel Professional Dimmers All dimming protocol 6 20 A, 3 Phase
L5106D5LP L5106D Range 6 Channel Professional Dimmers All dimming protocol 6 30 A, 1 Phase; 10 A, 3 Phase
L5106D3LP L5106D Range 6 Channel Professional Dimmers All dimming protocol 6 20A , 1 phase
L5103D20LP L5103D Range 3 Channel Professional Dimmers All dimming protocol 3 20 A, 3 Phase
L5103D10LP L5103D Range 3 Channel Professional Dimmers All dimming protocol 3 30 A, 1 Phase ; 10 A, 3 Phase
L5103D5LP L5103D Range 3 Channel Professional Dimmers All dimming protocol 3 15 A, 1 Phase

Table 2-1Clipsal C-bus high power dimmers

Part number Name Dimming Protocal No. of Channel Current Rating
L5504D2U 4 Channel Universal Dimmer with Power Supply Universal 4 2A
L5504D2UP 4 Channel Universal Dimmer Universal 4 2A
L5504D2A 4 Channel Dimmer with Power Supply Leading edge 4 2A
L5504D2AP 4 Channel Dimmer  Leading edge 4 2A
L5508D1A 8 Channel Dimmer with Power Supply Leading edge 8 1A
L5508D1AP 8 Channel Dimmer Leading edge 8 1A
L5504AMP 0-10V Analogue Output Unit  0-10V 4 25mA

Table 2-2 Clipsal C-bus Analogue dimmers

 

Part number Name Dimming Protocal No. of Channel Current Rating
 L5508DSI 8 Channel DSI Gateway with Power Supply DSI 8 200mA
L5508DSIP 8 Channel DSI Gateway DSI 8 18mA
5502DAL 2 Channel DALI Gateway for C-Bus DALI 2 32mA
5500DMX C-Bus DMX Gateway DMX 1 for 40 units 50mA

Table 2-3 Clipsal C-bus Digital dimmers

[1] http://www2.clipsal.com/cis/technical/product_groups/cbus

[2]  http://www2.clipsal.com/cis/technical/technical_support/training2/cbus_control_and_management_system/basic

[3] http://www2.clipsal.com/cis/technical/downloads/c-bus_toolkit

How to Choose a Dimmable LED ?

The rising cost of electricity is certainly driving consumers, retailers and business owners to seek for energy-efficient lighting technologies, and dimmable LED is considered as one of the most efficient choices. However, as people may know, there are a huge amount of different dimmable LEDs in the Australian market, and the dimming methodology for all these products are varied. When facing this massive amount of options, consumers are frequently encounter such question: Which dimmable LED should I choose?

How LED lights be dimmed?

Before answering this question, it is necessary to clarify that most of LED lamps are powered by electronic drivers, as they are more suitable for DC device. In general, there are mainly 4 protocols that are using in Australia:

1.     Phase-cut dimming

This method dims the output illuminance through cutting the phase of the AC current, which will decrease the power input to the light. There are mainly four types of phase-cut dimming methods:

a.    Leading Edge dimming:

This can be alternatively called as “TRIAC dimming” or “incandescent dimming”. It turns off the sinusoidal signal of the electrical current at the front of the AC input. It fits the traditional incandescent lamps or magnetic low voltage transformer. Nevertheless, it can cause buzzing noise when dimmed, and when it is used for an LED lamp, it can produce a high inrush current to its electronic component, and eventually the entire luminaire will be damaged. [1]

b.    Trailing Edge

This is also called “electronic dimming”, which can be considered as a reverse form of leading edge dimming, as it turns of the end of the AC input waveform. It can be used for electronic driver and low voltage transformers. In comparison to leading edge dimming, it will not exert high inrush current, while not causing buzzing sound when dimmed.[2]

Summary for phase-cut dimming

After comparing these two Phase-cut dimming methodologies, it is clear that for most LED lamps, trailing edge dimming is a better option comparing to leading edge dimming. However, because LED retrofits are mostly for the existing incandescent or halogen fixtures, which makes many manufacturers designed their LED lamps to be suitable for leading edge dimmer. So when you choosing a dimmable LED, it is better to clarify the capable dimming method for the product before getting a dimmer for it, or you can use a “Universal” dimmer, as it is suitable for both leading edge and trailing edge dimming.

2.     0-10V analogue:

As one of the earliest and simplest lighting control, 0-10V analogue dimming is used for early fluorescent dimming and still being used today. Nowadays, some of the LED fixture is also designed for this dimming methodology due to its simplicity. This 0-10V dimmer is connected to the circuit in parallel, and dims LED simply by adjusting the input to the lamp via scaling the DC voltage at the dimmer side. Theoretically, the LED will have 100% output when the dimmer is scaled at 10V; while the dimmer is at 0V, the LED will have 0% output, or be turned “OFF”. However, in many cases, the light can only be dimmed down to 10% due to the limitation of the power supply, and a switch or relay is needed to completely turn the light off. [3] Moreover, for a 0-10V dimming system, each control channel requires one wire, and the excessive amount of cabling can cause a considerable voltage drop that lowered the energy efficiency. [4]

3.     Pulse Wave Modulation (PWM) Dimming

In a technical perspective, PWM dimming can be categorised as a type of Digital dimming. Instead of adjusting the DC current, PWM dimming achieve the same effect by varying the duty cycle of the constant current. It switches the input current of the LED lamp at a high frequency between 0A and the rated current, and this modification of on-off rate of LED will result as the change of output percentage. This suitable for LEDs that need to maintain colour consistency when dimmed down to lower than 40%, and lighting applications with mixed colour control. Nevertheless, in order to be capable with a PWM dimmer, the power supply should be able to run the LED at a high enough frequency, and this will greatly increase the technical requirement of an LED driver[5].

4.     Digital Dimmings

(1)  DSI and DALI Control

The reason that I put these two dimming protocol together is that they are both developed under the working principle of 0-10V analogue lighting control.

DSI( “Digital Series Interface”) dimming technology is uniquely owned by Tridonic®, and it has been used for the control of LED interface or electronic Fluorescent ballast. This is also the precursor to DALI dimming system. [6]

On the other hand, although DALI is developed based on DSI protocol, it is a non-propertied technology, so it is now the most common type of commercial lighting control system, which is available from many different suppliers. Each DALI device has a “non-violate” memory, which contains its own settings. This allows DALI to operate without a central control point. [7]

(2)  Switch dimming

This is a stand-along digital protocol. It is a cheap solution that is commonly used for residential and hospitality systems. No control system is required for this type of dimmer.

(3)  DMX Dimmer

DMX (or “DMX512”) is the digital control system that is designed for RGB and RGBW colour change lighting system.Different from other digital systems, it allows complicated programming to communicate DMX devices through a ‘Data Bus’. It sends signal in an 8/16bit code package, which can instruct fixtures on everything from dimming to movement positions. All this feature makes it an ideal option for stage lighting and effect industry[8].

C-Bus……?

Although there are lots of people asking questions about “C-bus dimming”, however it is not a dimming protocol. This is actually a building control system that is owned by Clipsal® Australia. Due to its complexity, I will talk about it in another separate article.

Summary

To sum up, the conventional dimming method can be summarized as table 1below. Hope this can give you a bit of idea when you choosing a dimmable LED.

Category DimmingProtocol Control system needed? (Y/N) Capability
Analogue Leading Edge N Incandescent Lamp; Fluorescent lamp with Iron-core ballast; LED with Leading edge dimming driver
Traling Edge N Halogen lamp;Fluorescent lamp with electronic Ballast;  Dimmable LED with electronic driver
0-10V dimming N halogen lamp;Fluorescent lamp with 0-10V Ballast;  Dimmable LED with 0-10V driver
Digital PWM Dimming N LED driver with high enough output frequency
Switch dimming N most of the single fixture dimming
DSI Y LED or other device with dimmable Drivers with DSI or 0-10V functions
DALI Y Most of major 0-10V ballast. LED or other device with dimmable Drivers with  DALI ,DSI or 0-10V functions
DMX Y RGB and RGBW LED control; Stage and effect lighting
 Table 1 summary for dimming methods
p.s.: One of the discussion of the C-bus community forum has been cited for the information above: 
http://www.cbusforums.com/forums/showthread.php?t=2626

Reference

[1] http://www.leapfroglighting.com/trailing-edge-or-leading-edge-led-dimming/

[2] http://www.leapfroglighting.com/trailing-edge-or-leading-edge-led-dimming/

[3] http://www.lightology.com/index.php?module=tools_faq_0_10v_control

[4] http://www.epanorama.net/documents/lights/0to10v.html

[5] http://www.lutron.com/TechnicalDocumentLibrary/048360a_PWM_vs_CCR_LED_App_Note.pdf

[6] http://lightproject.com.au/the-basics-dimming

[7] http://lightproject.com.au/the-basics-dimming

[8] http://lightproject.com.au/the-basics-dimming

Declaration

Hi Everyone!

Before posting anything, I would like to make a short declaration.The purpose of this blog is only to share my knowledge of lighting, also the new ideas that I got from own experience and the books that I read.

In order to avoid conflict of interest, also to show respect to others, I will make clear citations for all resources that I had used to write my articles.

Finally, if you have any questions, or find anything wrong in my articles, you are more than welcome to leave me an email at: Steve.law@paklighting.com.au. As a young engineer who is eager to learn, I am more than happy to offer my assistant and get myself improved.

Anyway, hope my articles can be useful and inspiring for you.

Yours Sincerely

Stevo