作者:電子時報 黃女瑛
太陽能電池目前最主要被應用在於發電領域，許多人或許想像，太陽光電的發展，就是一塊一塊趕快把太陽能模組架在地球表面，吸收陽光以達到發電目的。所以許多業者積極的擴充產能，以搶攻市場佔有率，但許多人卻忽略了，它的轉換效率對產業發展有十分關鍵的影響，太陽光電的發展其實是一個技術規模戰，而非傳統量產規模戰，廠商未達一定水準的轉換效率，同樣會被迫退出市場。油價高漲，替代能源的重要性跟著與日俱增，太陽光電也跟著一路受重視，許多人或許會想像，架設一片片朝著陽光的太陽能系統發電，填滿所有可架設的地球表面或是屋頂，就是太陽能發電成為主流發電的時候。
許多業者也積極朝量產規模化前進，期以透過量產規模來降低生產成本，並得以快速搶攻市場佔有率，但又受限於多晶矽料源的缺乏，所以一張張的高價長期合約因應而生，一聲聲的叫價讓料源現貨市場的價格火速上揚。不過，在太陽光電熱翻天的當下，多數人甚至是業者都是醉心在迷人的股價表現上，編織各類再生能源美夢，吸引一波波的資金流入，卻忘了它其實還是個受各國政府獎勵才能運作的產業，從歷史的演變來看，這種產業其實還只是政府懷中受呵護的嬰幼兒產業，去掉政府的幫助恐怕連走都有困難。太陽光電仍需受政府補助的主要原因來自於它的發電成本仍然高於傳統發電方式，尤其是電價偏低的國家更是難以推行。要降低太陽能發電成本，最根本的方法就是快速提升轉換效率，轉換效率高，同面積的發電量就高，系統所佔用的土地、空間面積就小，成本相對就低，以結晶矽太陽能電池來看，提升1%轉換效率可以降低7%的總成本，所以達到相當的轉換效率水準才有機會與傳統電價做比較，不論是結晶矽太陽能電池或薄膜太陽能電池，最終的目標就是達到與傳統電價相同的發電成本。
可以預知的是，太陽光電的發展是一場技術規模戰而不是量產規模戰，因為太陽能電池的種類繁多，包括結晶矽、非晶矽、砷化鎵及其它薄膜等，均在力拼轉換效率及降低成本。太陽能發電成本包括系統售價、佔地面積及維修費用等，這些加總所產生的每瓦電發電成本是否能與傳統電價每瓦發電成本相抗衡，而不是一片片架設加總起來，大到幾乎可遮天的太陽能發電系統，卻僅可以發出微薄的電力。各國政府補助的美意近年來也受到相當的檢討，因為許多人覺得它只不過是圖利廠商，人民並未受到該項利益。
降低太陽能發電成本更成了該產業發展的當務之急，轉換效率更被視為是中、長期最根本的解決方案，而這卻攸關各個業者本身的研發能力，惟有不斷的壯大本身的研發能力才能夠與國際大廠相抗衡，它的技術規模化走勢其實從很多國際大廠不斷發表突破轉換效率的訊息可以看出。其實2007年消費者的消費行為已經透露轉換效率的重要性，低轉換效率的太陽能電池有些被要求極大的折扣，有些則直接被列為可丟棄的產品，未來，缺料、缺貨問題不再時，轉換效率不符合水平者，恐怕直接被市場所淘汰。轉換效率提升必須也被納入擴產的目標中，一條條產能線的擴增，就該使轉換效率跟著一步一步的增加，而不是只把企圖心放在產能拼第幾大，試想，一旦無法跟上市場快速成長的轉換效率，這些年來快速架設的龐大產能設備，所簽定的多張昂貴長期料源合約，將會是多麼驚人的負擔？如果以為如同以往的規模量產可以再造新帝國，最後都會因為技不如人被迫苟延殘喘，未來產生泡沬化的日子也不遠。
2007年11月28日 星期三
2007年11月27日 星期二
綠色議題抬頭 能量採集IC前景看好
短評:
這篇短文的附屬簡評中,有人看衰這門技術:針對其熱電或壓電能量採集太過微量而不具可行性.
基本上這門技術的可行性關鍵不在那微小的元件到底能轉換出多少可用的能量,而是在此轉換能量的材料其最佳效率為何.再者就是要如何對此種材料加工
無論是熱電材料還是壓電材料,其基本研究都始於百多年前科學家對物理現象的觀察.其原理主要在環境的"熱"造成材料晶格的振動使電子能掙脫核力的束縛,因而產生電能.這種能量自然不夠多.轉換效率自然也低.
何謂聚沙成塔?何謂積少成多? 一小粒元件只能發40mw--如果是10粒,如果是100粒呢?所以要多點能量,就該讓這種轉換單元聚集得更有規模些.
要知道,能量每經過一個傳遞介面就會有耗損,即使在單一材料內傳遞,能量的損耗也相當可觀;所以當一系統內所有的單元都需要人為地輸入能量驅動,所有的能量損耗加總起來就相當大;如果內中許多的小單元並不需要"大"能量,只要微量地40mw的電能就能驅動,則吾人大可讓這樣的小單元搭配一粒所謂的能量採集單元,讓中央處理器或是壓降電晶體產生的高熱成為驅動的能量源;我們只需對CPU等需大能量的單元輸入驅動能就可以了.如此每一組系統能節省下的能量即使不夠高,全球上億台系統所能節省的能量依定非常可觀.
節能不只要從大處著眼,從小地方也能發揮到環保節能的精神.
------------------------------
by Christoph Hammerschmidt
隨著能源議題的發燒，業者開始構想開發能夠從環境中採集能量的自我供電系統，因此催生了一場開發能量採集技術和標準的競賽。在很多應用中，環境自身可以透過溫度差異、振盪或光線來能夠提供所需的能量。
由於能量採集器一般需要很長時間才能夠採集到很少的能量，而這些能量隨後又會被感測器上的資料傳輸系統損耗，因此在很多情況下採集器都帶有一個電容器來作為能量存儲子系統。在飛機製造、個人健康監控系統或防盜竊檢測系統等各種應用中，能量採集－或者說能量聚集，將形成一個規模可能達到數十億美元的市場。
柏林研究諮詢公司VDI/VDE Innovation + Technik GmbH“獨立微系統”研究專案負責人Marco Voigt表示，由於能量採集的重要性，已經被德國聯邦政府納入其總值約6.85億美元的研究支援專案中。
有關能量採集的研究已經展開了。例如，Fraunhofer積體電路研究院就展出了一個基於半導體的熱力發電機(TEG)，可以將溫差轉換成電能。這一設備佩帶在人身上，利用人體熱量作為能量來源。
另外，IMEC荷蘭分部最近也在利用壓電效應來開發一個能源採集設備。該設備將機械振盪轉換成大約40mw的電能。
IMEC研究人員Bert Gyselinckx表示，如今的壓電元件所用的材料都是鋯鈦酸鉛(PZT)。但是，這一材料在大規模生產時是很難處理的。他希望這一問題能在未來五年內解決，而壓電能量採集器也能實現工業化生產。
還有一些公司則已經取得了更大的進展。比如，Perpetuum公司的能量採集器就已經進入了商業化生產階段。該公司的CEO Roy Freeland表示：“我們主要是透過一個磁圈系統來將振盪轉換成電能。”
Freeland將振盪能和動能區分開來。他說：“按照我們的定義，動能的頻率只有大約1Hz，是非常低的，和心跳頻率差不多。”Perpetuum公司目前在開展的一個動能研究專案－用於病人監測系統的能量採集器，就是利用了這一點。目前Perpetuum公司的能量採集系統產量不高，而另一家公司則已經進入了大規模生產。
EnOcean公司已經在供應電力動態能量轉換器，這種轉換器與開關無線連接，因此開關可以放置於室內的任何地方，不需要電池。按動按鍵所需的能量被轉換成無線發射器的電能，該發射器可以觸發電路來開關室內的燈光。EnOcean公司行銷經理Zeljko Angelovski表示，雖然這種產品可能會被看作是種擺設，但該公司已經賣出了數萬台。
但是，能量採集器的突破並沒有到來。Wicht公司的分析人士Bouchaud表示，從數量上來看，這一技術的最大市場應該是胎壓監控系統(TPMS)，預計應用於MEMS技術的TPMS系統將在2012年左右開始快速發展。傳統的TPMS是採用昂貴且笨重的電池來供電的，這也是TPMS中成本最大的元件。而新型TPMS則採用了振盪能量採集器，可以從輪緣上移動到輪胎內部，以獲得除壓力之外的更多資訊，使得智慧化輪胎能採集並發送輪胎氣壓、牽引力、磨損、溫度等更多資料。
這篇短文的附屬簡評中,有人看衰這門技術:針對其熱電或壓電能量採集太過微量而不具可行性.
基本上這門技術的可行性關鍵不在那微小的元件到底能轉換出多少可用的能量,而是在此轉換能量的材料其最佳效率為何.再者就是要如何對此種材料加工
無論是熱電材料還是壓電材料,其基本研究都始於百多年前科學家對物理現象的觀察.其原理主要在環境的"熱"造成材料晶格的振動使電子能掙脫核力的束縛,因而產生電能.這種能量自然不夠多.轉換效率自然也低.
何謂聚沙成塔?何謂積少成多? 一小粒元件只能發40mw--如果是10粒,如果是100粒呢?所以要多點能量,就該讓這種轉換單元聚集得更有規模些.
要知道,能量每經過一個傳遞介面就會有耗損,即使在單一材料內傳遞,能量的損耗也相當可觀;所以當一系統內所有的單元都需要人為地輸入能量驅動,所有的能量損耗加總起來就相當大;如果內中許多的小單元並不需要"大"能量,只要微量地40mw的電能就能驅動,則吾人大可讓這樣的小單元搭配一粒所謂的能量採集單元,讓中央處理器或是壓降電晶體產生的高熱成為驅動的能量源;我們只需對CPU等需大能量的單元輸入驅動能就可以了.如此每一組系統能節省下的能量即使不夠高,全球上億台系統所能節省的能量依定非常可觀.
節能不只要從大處著眼,從小地方也能發揮到環保節能的精神.
------------------------------
by Christoph Hammerschmidt
隨著能源議題的發燒，業者開始構想開發能夠從環境中採集能量的自我供電系統，因此催生了一場開發能量採集技術和標準的競賽。在很多應用中，環境自身可以透過溫度差異、振盪或光線來能夠提供所需的能量。
由於能量採集器一般需要很長時間才能夠採集到很少的能量，而這些能量隨後又會被感測器上的資料傳輸系統損耗，因此在很多情況下採集器都帶有一個電容器來作為能量存儲子系統。在飛機製造、個人健康監控系統或防盜竊檢測系統等各種應用中，能量採集－或者說能量聚集，將形成一個規模可能達到數十億美元的市場。
柏林研究諮詢公司VDI/VDE Innovation + Technik GmbH“獨立微系統”研究專案負責人Marco Voigt表示，由於能量採集的重要性，已經被德國聯邦政府納入其總值約6.85億美元的研究支援專案中。
有關能量採集的研究已經展開了。例如，Fraunhofer積體電路研究院就展出了一個基於半導體的熱力發電機(TEG)，可以將溫差轉換成電能。這一設備佩帶在人身上，利用人體熱量作為能量來源。
另外，IMEC荷蘭分部最近也在利用壓電效應來開發一個能源採集設備。該設備將機械振盪轉換成大約40mw的電能。
IMEC研究人員Bert Gyselinckx表示，如今的壓電元件所用的材料都是鋯鈦酸鉛(PZT)。但是，這一材料在大規模生產時是很難處理的。他希望這一問題能在未來五年內解決，而壓電能量採集器也能實現工業化生產。
還有一些公司則已經取得了更大的進展。比如，Perpetuum公司的能量採集器就已經進入了商業化生產階段。該公司的CEO Roy Freeland表示：“我們主要是透過一個磁圈系統來將振盪轉換成電能。”
Freeland將振盪能和動能區分開來。他說：“按照我們的定義，動能的頻率只有大約1Hz，是非常低的，和心跳頻率差不多。”Perpetuum公司目前在開展的一個動能研究專案－用於病人監測系統的能量採集器，就是利用了這一點。目前Perpetuum公司的能量採集系統產量不高，而另一家公司則已經進入了大規模生產。
EnOcean公司已經在供應電力動態能量轉換器，這種轉換器與開關無線連接，因此開關可以放置於室內的任何地方，不需要電池。按動按鍵所需的能量被轉換成無線發射器的電能，該發射器可以觸發電路來開關室內的燈光。EnOcean公司行銷經理Zeljko Angelovski表示，雖然這種產品可能會被看作是種擺設，但該公司已經賣出了數萬台。
但是，能量採集器的突破並沒有到來。Wicht公司的分析人士Bouchaud表示，從數量上來看，這一技術的最大市場應該是胎壓監控系統(TPMS)，預計應用於MEMS技術的TPMS系統將在2012年左右開始快速發展。傳統的TPMS是採用昂貴且笨重的電池來供電的，這也是TPMS中成本最大的元件。而新型TPMS則採用了振盪能量採集器，可以從輪緣上移動到輪胎內部，以獲得除壓力之外的更多資訊，使得智慧化輪胎能採集並發送輪胎氣壓、牽引力、磨損、溫度等更多資料。
2007年11月26日 星期一
Illuminating evidence - a breakthrough in power LED lifetime data helps manufacturers build and deploy reliable lighting solutions
A graphical representation of lifetime in terms of both drive current and junction temperature provides the optimum data for designers, says Steve Landau of Philips Lumileds.
-------------------
The design benefits of using power LEDs to replace traditional incandescent light sources are undoubtedly powerful. Smaller, more efficient, longer-lasting, they can enable economic or functional improvements to existing lighting equipment, and enable types of lighting that were never before possible.
For all the obvious benefits, however, there are also hurdles for the user to overcome before completing a successful design with power LEDs. One of the most significant of these is determining the relationship between drive current, thermal management and effective lifetime of a luminaire or installation that uses power LEDs.
It is this challenge that Philips Lumileds has sought to address with a new category of lifetime and reliability data. This new data set improves on the industry-norm information on lumen maintenance that power LED manufacturers have presented to date. And designers who have used the new data give strong backing for claims that it is easier to work with, and provides a higher level of confidence in operational lifetime forecasts.
B and L lifetime data
Every lighting designer is familiar with the 'mean time between failure (MTBF)' data commonly provided by conventional lamp manufacturers. Lighting designers use MTBF as a guideline to determine when re-lamping must occur. Such a simple rating is appropriate for conventional lamps, which tend to fail catastrophically after a relatively short period of time.
Power LEDs, however, behave differently; they rarely fail completely, but instead their light output declines gradually over a long period as a function of drive current and temperature. Thus the simple MTBF figure applied to conventional lamps is inapplicable to power LEDs.
Indeed, the complex relationship between drive current, temperature and light output makes it much more difficult for lighting companies to accurately model the behaviour of power LED systems than it is to model the behaviour of conventional lighting systems. To solve this problem, Philips Lumileds devised a new tool based in part on research by the Alliance for Solid State Illumination Systems and Technologies (ASSIST).
This new 'graphical reliability data' model consists of two parts, a statement of failure (B) and a statement of lumen maintenance (L). Failure in the case of a power LED is defined as lumen maintenance below a specified level. (It should be noted that, unlike the conventional lamp model, even when an LED is considered a ‘failure’ it is likely to still be providing useful light output.)
L is the minimum acceptable lumen maintenance figure as required by the application. So, if L = 70 (70% lumen maintenance) then an LED will be considered a failure if its lumen maintenance is 69% or lower.
Using these definitions, we can begin to describe the lifetime behaviour of power LEDs. For instance, if the LEDs are rated for B50/L70 at 50,000 hours, then we would expect that half of the LEDs in an array would have lumen maintenance below 70% at 50,000 hours.
Graphical representation
While this B50/L70 measure has the benefit of being clear, on its own it is not sufficient to enable the designer to optimise an LED lighting design. This is because both the operational lifetime of power LEDs and their light output are dramatically affected by two factors: one is drive current – how much power you supply to the device; and the other is temperature, both ambient and internal to the LED.
Lighting engineers have to weigh up their system’s costs and performance requirements, and find a balance between the number of LEDs, drive current and temperature that provides the best commercial outcome.
In other words, for each luminaire design, a specified amount of light is required: this can be achieved by using fewer LEDs driven at a higher current, or more LEDs driven at a lower current.
But how much does a decrease in drive current extend the LEDs’ lifetime? How much heat needs to be extracted from the light source in order to hit the designer’s target lifetime?
For all the obvious benefits, however, there are also hurdles for the user to overcome before completing a successful design with power LEDs. One of the most significant of these is determining the relationship between drive current, thermal management and effective lifetime of a luminaire or installation that uses power LEDs.
It is this challenge that Philips Lumileds has sought to address with a new category of lifetime and reliability data. This new data set improves on the industry-norm information on lumen maintenance that power LED manufacturers have presented to date. And designers who have used the new data give strong backing for claims that it is easier to work with, and provides a higher level of confidence in operational lifetime forecasts.
B and L lifetime data
Every lighting designer is familiar with the 'mean time between failure (MTBF)' data commonly provided by conventional lamp manufacturers. Lighting designers use MTBF as a guideline to determine when re-lamping must occur. Such a simple rating is appropriate for conventional lamps, which tend to fail catastrophically after a relatively short period of time.
Power LEDs, however, behave differently; they rarely fail completely, but instead their light output declines gradually over a long period as a function of drive current and temperature. Thus the simple MTBF figure applied to conventional lamps is inapplicable to power LEDs.
Indeed, the complex relationship between drive current, temperature and light output makes it much more difficult for lighting companies to accurately model the behaviour of power LED systems than it is to model the behaviour of conventional lighting systems. To solve this problem, Philips Lumileds devised a new tool based in part on research by the Alliance for Solid State Illumination Systems and Technologies (ASSIST).
This new 'graphical reliability data' model consists of two parts, a statement of failure (B) and a statement of lumen maintenance (L). Failure in the case of a power LED is defined as lumen maintenance below a specified level. (It should be noted that, unlike the conventional lamp model, even when an LED is considered a ‘failure’ it is likely to still be providing useful light output.)
L is the minimum acceptable lumen maintenance figure as required by the application. So, if L = 70 (70% lumen maintenance) then an LED will be considered a failure if its lumen maintenance is 69% or lower.
Using these definitions, we can begin to describe the lifetime behaviour of power LEDs. For instance, if the LEDs are rated for B50/L70 at 50,000 hours, then we would expect that half of the LEDs in an array would have lumen maintenance below 70% at 50,000 hours.
Graphical representation
While this B50/L70 measure has the benefit of being clear, on its own it is not sufficient to enable the designer to optimise an LED lighting design. This is because both the operational lifetime of power LEDs and their light output are dramatically affected by two factors: one is drive current – how much power you supply to the device; and the other is temperature, both ambient and internal to the LED.
Lighting engineers have to weigh up their system’s costs and performance requirements, and find a balance between the number of LEDs, drive current and temperature that provides the best commercial outcome.
In other words, for each luminaire design, a specified amount of light is required: this can be achieved by using fewer LEDs driven at a higher current, or more LEDs driven at a lower current.
But how much does a decrease in drive current extend the LEDs’ lifetime? How much heat needs to be extracted from the light source in order to hit the designer’s target lifetime?
It is these questions that Philips Lumileds’ new graphical reliability data answers (see figure 1). Presented as two-axis graphs, the lumen maintenance curves allow the lighting designer quickly and easily to plot the perfect combination of drive current and temperature in relation to lifetime for their application.
The plot of B/L data can be described for virtually any combination. Certain applications – such as wall washing – cannot tolerate as much as 30% degradation in light output, and can require 80% or 90% lumen maintenance typically. Others – such as decorative lighting – can sustain a degradation of as much as 50% of peak light output, so different representations are made for different combinations of B and L.
Ensuring compliance
One long-time power LED user that has used these new data sets is IST Ltd, a professional lighting company specialising in innovative architectural and entertainment lighting solutions. IST is on the verge of strengthening its commercial and domestic product offering with the launch of a range of downlighters which use LUXEON Rebel power LEDs.
Guaranteeing the level of light output for the lifetime of IST’s products is essential because its downlighter is designed to be ‘Part L’-compliant. This latest version of the regulatory document for new buildings in the UK came into effect in April 2006. This regulation includes provisions for the efficiency of light fittings, and their absolute light output.
Matt Fitzpatrick, director of IST, explains: "For commercial applications you need to reach 45 lumens/Watt, for domestic you need 40lm/W. The downlighter market is a high-volume, attractive market to play in, but to get adoption you need it as aggressively priced as possible while also meeting the requirements for Part L."
This presents a difficult design challenge: by driving fewer LEDs harder, IST could reduce the cost of the product, but this could put at risk Part L compliance if it meant lumen maintenance was compromised and total light output too quickly dropped below that specified by the regulations.
By the same token, if the company played safe – using many more LEDs at a greatly reduced drive current in order to greatly prolong peak lumen output – the cost of the product would go up beyond what the market could accept. It was essential to get the balance exactly right.
IST’s Fitzpatrick says that the data from Philips Lumileds allowed product designers to do a comprehensive cost/performance comparison on designs using different numbers of LEDs at different drive currents, using temperature data that they were able to get from prototypes.
"Based on the information from Philips Lumileds, I know what the light output is going to be and how many LEDs I need to put in to the product to get the light output I want, over the operational lifetime that I am guaranteeing to customers. It is exactly the kind of information that I believe the industry has been looking for," he says.
The ready availability of such data has given IST an important competitive edge, allowing it to get to market faster after a shorter research and development process. As Fitzpatrick explains, "without this information we would have to do more development work and more practical experimentation with prototypes to understand exactly how the LED performed over time in our application."
Predicting lifetime
The impact of comprehensive lifetime data is also imperative in applications where premature failure could be commercially damaging. Chromatica, an architectural lighting manufacturer, has been working with power LEDs for more than three years. It was recently responsible for what, at the time, was the largest installation utilising Rebel LEDs in the world: an architectural lighting installation for an office complex comprising in excess of 35,000 LEDs.
Kevin Clark, director of Chromatica, explains: "It is critical to have factual information to predict the “end of life”, which for us means performance after 50,000 hours of operation. We guarantee our products for this duration, so we in turn have to be able to rely on our LED supplier’s data."
Clark says that this is a key reason Chromatica primarily uses LUXEON LEDs. "In our experience, Philips Lumileds supplies the most comprehensive data sets for power LEDs in the industry," he says.
The Philips Lumileds reliability tools are distinguished by their ability to predict operational lifetimes in any combination of the two key variables: drive current and temperature. If Chromatica were to use different data sets that did not expose the effect of current and temperature differences, the company would risk making false assumptions about the operational lifetime of its light sources. This in turn could lead to costly in-warranty failures – a commercially disastrous consequence of poor rating data.
The alternative would be to withhold or limit the lifetime warranty. As Clark says, such installations are "not the type of application we want to target, as the price pressures in them are much tighter."
Indeed, cases such as Chromatica’s highlight the importance for LED users of understanding the validity of the rating data that vendors supply.
Accurate statistics
Using the Weibull distribution function – a universally respected statistical technique – to extrapolate product performance, the data from Philips Lumileds shows an extremely low divergence between forecasted and actual performance. Based on the quantity of data it now holds, and using extremely prudent statistical principles, Philips Lumileds is able to accurately predict lumen maintenance for 60,000 hours with a 90% confidence rate. It is worth noting that data from fewer parts on test for fewer hours would support performance predictions that extended less far into the future.
The experiences of IST and Chromatica show that power LED customers should be aware of the parameters that affect device lifetimes, and demand that their suppliers provide comprehensive data showing the interactions of average lifetime, lumen maintenance, drive current and temperature.
Only by understanding and applying this crucial data can manufacturers and their customers continue to develop reliable lighting solutions that can be guaranteed for the whole of their intended lifetime.
About the Author
Steve Landau is Director of Marketing Communications with Philips Lumileds Lighting Company, San Jose, California.
The plot of B/L data can be described for virtually any combination. Certain applications – such as wall washing – cannot tolerate as much as 30% degradation in light output, and can require 80% or 90% lumen maintenance typically. Others – such as decorative lighting – can sustain a degradation of as much as 50% of peak light output, so different representations are made for different combinations of B and L.
Ensuring compliance
One long-time power LED user that has used these new data sets is IST Ltd, a professional lighting company specialising in innovative architectural and entertainment lighting solutions. IST is on the verge of strengthening its commercial and domestic product offering with the launch of a range of downlighters which use LUXEON Rebel power LEDs.
Guaranteeing the level of light output for the lifetime of IST’s products is essential because its downlighter is designed to be ‘Part L’-compliant. This latest version of the regulatory document for new buildings in the UK came into effect in April 2006. This regulation includes provisions for the efficiency of light fittings, and their absolute light output.
Matt Fitzpatrick, director of IST, explains: "For commercial applications you need to reach 45 lumens/Watt, for domestic you need 40lm/W. The downlighter market is a high-volume, attractive market to play in, but to get adoption you need it as aggressively priced as possible while also meeting the requirements for Part L."
This presents a difficult design challenge: by driving fewer LEDs harder, IST could reduce the cost of the product, but this could put at risk Part L compliance if it meant lumen maintenance was compromised and total light output too quickly dropped below that specified by the regulations.
By the same token, if the company played safe – using many more LEDs at a greatly reduced drive current in order to greatly prolong peak lumen output – the cost of the product would go up beyond what the market could accept. It was essential to get the balance exactly right.
IST’s Fitzpatrick says that the data from Philips Lumileds allowed product designers to do a comprehensive cost/performance comparison on designs using different numbers of LEDs at different drive currents, using temperature data that they were able to get from prototypes.
"Based on the information from Philips Lumileds, I know what the light output is going to be and how many LEDs I need to put in to the product to get the light output I want, over the operational lifetime that I am guaranteeing to customers. It is exactly the kind of information that I believe the industry has been looking for," he says.
The ready availability of such data has given IST an important competitive edge, allowing it to get to market faster after a shorter research and development process. As Fitzpatrick explains, "without this information we would have to do more development work and more practical experimentation with prototypes to understand exactly how the LED performed over time in our application."
Predicting lifetime
The impact of comprehensive lifetime data is also imperative in applications where premature failure could be commercially damaging. Chromatica, an architectural lighting manufacturer, has been working with power LEDs for more than three years. It was recently responsible for what, at the time, was the largest installation utilising Rebel LEDs in the world: an architectural lighting installation for an office complex comprising in excess of 35,000 LEDs.
Kevin Clark, director of Chromatica, explains: "It is critical to have factual information to predict the “end of life”, which for us means performance after 50,000 hours of operation. We guarantee our products for this duration, so we in turn have to be able to rely on our LED supplier’s data."
Clark says that this is a key reason Chromatica primarily uses LUXEON LEDs. "In our experience, Philips Lumileds supplies the most comprehensive data sets for power LEDs in the industry," he says.
The Philips Lumileds reliability tools are distinguished by their ability to predict operational lifetimes in any combination of the two key variables: drive current and temperature. If Chromatica were to use different data sets that did not expose the effect of current and temperature differences, the company would risk making false assumptions about the operational lifetime of its light sources. This in turn could lead to costly in-warranty failures – a commercially disastrous consequence of poor rating data.
The alternative would be to withhold or limit the lifetime warranty. As Clark says, such installations are "not the type of application we want to target, as the price pressures in them are much tighter."
Indeed, cases such as Chromatica’s highlight the importance for LED users of understanding the validity of the rating data that vendors supply.
Accurate statistics
Using the Weibull distribution function – a universally respected statistical technique – to extrapolate product performance, the data from Philips Lumileds shows an extremely low divergence between forecasted and actual performance. Based on the quantity of data it now holds, and using extremely prudent statistical principles, Philips Lumileds is able to accurately predict lumen maintenance for 60,000 hours with a 90% confidence rate. It is worth noting that data from fewer parts on test for fewer hours would support performance predictions that extended less far into the future.
The experiences of IST and Chromatica show that power LED customers should be aware of the parameters that affect device lifetimes, and demand that their suppliers provide comprehensive data showing the interactions of average lifetime, lumen maintenance, drive current and temperature.
Only by understanding and applying this crucial data can manufacturers and their customers continue to develop reliable lighting solutions that can be guaranteed for the whole of their intended lifetime.
About the Author
Steve Landau is Director of Marketing Communications with Philips Lumileds Lighting Company, San Jose, California.
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