A trick between Lumens and Wattage of LED Flashlight

Why is a 3W LED torch much brighter than 25W or higher wattage LED flashlight?

The first trick is,1ST quality LED chip from, for example, CREE can offer 100~110 Lm/W

Cheaper chip from lower-class suppliers can only offer 45~50 Lm/W

That’s why even though more wattage is consumed to burn the LED chip, but it’s not as bright as expected.

In the other words, the wattage of LED is absolutely not a main issue we should concern when we pick up a LED lamp. LED Technology is really hot subject nowadays, but it’s still in “Growing Phase”, all the LED technology is going faster day by day.

Therefore, there is a big gap between both 3W LED chips but from different manufacturers, i.e. CREE and other small producers. This phenomenon can be used to explain that why over 3 times cost difference between quality (100~110 Lm/W) chip and cheap (45~50 Lm/W) one. Due to this bulky cost difference, right now we can find the cheap chip still survives in the market, and cause a lot of brummagem LED flashlights appear in the market.

How to recognize LED chip is quality or cheap one?

Pls follow the instructions as following to reveal the trick between Lumens and Illumination.

To check the Lumens emits from the LED chip, you need a lumen meter to measure it.

  1. To check the wattage that the LED chip consumes, normally you can find it out in the Product description.
  2. If you get both value as above, now you can understand how is efficiency (Lumens/Wattage) of the LED chip.

Result:

  1. If the LED chip efficiency is over 100 LM/W, congratulation, you have a quality and Energy Conservation product.
  2. If the LED chip efficiency is under 100 LM/W, you can have it at cheaper price.

The second trick is,

There is the biggest secret from manufacturer, and no one will tell you this!

Heat, is the main issue in LED technology. Heat not only shortens the LED chip’s life, but also decreases Lumens of LEDs.

Normally says, when current (ampere) increases, LED output should also raises up (see the left figure as below.) But in the mean time, the heat will increase a lot, too. It will cause light decay (see the right figure as below.) It means when current is increased up to a limit level even though you keep increasing current, the Lumens of LEDs won’t be raised up any more, on the contrary, Lumens decreases in this situation.

流明及亮度的差別

我們3W為什麼比市售5W還亮?分析原因是:我們當時選用的LED晶粒,亮度是100~110Lm/W (流明/瓦),而我們估計市售買到的LED晶粒應該是亮度在50Lm/W左右的,也就是發光效率較差一些的晶粒, 所以即使是驅動到5W, 亮度依然比3W的低, 同時還多耗了2W的電力。

這也就是說,目前LED燈,絕對不是像一般鎢絲燈泡或螢光燈,這些鎢絲燈、鹵素燈、日光燈或螺旋節能燈,經過幾十年甚至上百年的研究改進,他們的發光效率已達到極限成熟也固定了,所以要亮一點就買W數大一點的,而LED卻還在成長期,發光效率還持續提升中,同時也因為不斷有新廠商投入LED晶粒的研發製造,各家的技術可是大不相同,技術差沒經驗的就製造了廉價級的,技術領先的就生產出黃金級的,以目前市場上還存在的LED晶粒等級, 40~50Lm/W和100~110Lm/W,這2種晶粒價差可是達到3倍。

照理說,技術都已經做到110Lm的晶粒了,怎麼還會有40Lm晶粒的市場及來源?技術不好經驗不足良率不佳的,當然就製造出這些”廉價級”的,不過即使是廉價也會有它的出路,而且可能是黃金路,LED燈外觀長像都差不多,甚至一模一樣,用低很多的成本,使用差一點的晶粒所組裝成的LED燈,一般人沒儀器設備那能分辦得出?

所以找有誠信的廠商購買是很重要的,同時現階段購買LED燈,千萬不能只看W數,陷入W數的迷思, 而是要看整體的亮度達到多少流明,這亮度符不符合需求?再看他的消耗功率是幾W。如果W數越小 那就代表越省電;如果1W的LED燈和5W的LED燈整體亮度是一樣的,價格也是一樣的,那當然是買1W的LED燈,比較省電,傻瓜才會堅持買5W的。那LED大概什麼時候會達到發光極限成熟期?讓一般人買LED燈,用W數就可以知道大概的亮度呢?

以目前科學家仍在努力的朝LED最高發光理論值220Lm/W研究開發,不過初期進步10分很容易,現在要進步1分都很困難,而且未來又不斷會有新廠商,把亮度低的實驗品倒入市場上,所以恐怕要好幾年, 或許是下輩子了…

另外,再提到LED是經由電流發出光,發光效率差同樣電流沒用來發光就用來發熱了,而熱如果沒有儘快排出散掉,光就越出不來,然後LED就熱衰減了,下面左圖是一般LED規格書裡都會有的圖, LED在導熱散熱足夠的條件下,所得到的曲線圖,隨著電流加大,發光亮度也幾乎呈線性提高。

下面右圖是一般人不知道的秘密,在這個LED的導熱散熱達到極限後,增加的電流不會再增加光輸出, 反而電流越增加,亮度越低,伴隨著LED溫度越高,最後就是迅速光衰熱死 !!

在我們以前研發產品過程中,有一個實例,同樣條件的LED燈,我們把一顆LED驅動700mA,另一顆驅動800mA,剛開始點亮馬上量測亮度, 800mA的亮度會高於700mA的LED燈,但是30分鐘熱平衡後再量測亮度, 2顆的亮度都下降了,不過700mA的亮度降得少一些,驅動800mA的亮度降低的幅度卻很大, 甚至亮度還低於700mA的亮度,也就是說驅動800mA已超過這個LED燈的導熱散熱極限了,多這100mA不但光出不來,亮度降低,溫度也提高,裡面電子零件壽命也會相對變短。

有些LED燈廠商會驅動較大電流,瞬間點亮的亮度比其它家來得高來誘使客戶購買,不過壽命恐怕就有問題了,所以購買LED燈的另一個重點,千萬不能被剛點亮時,比較高的亮度所迷惑,必須點亮30分鐘熱平衡後,比較前後亮度的衰減幅度,依照我們經驗,如果達到20%,那這個燈光衰會很快壽命不長久(LED壽命是以亮度光衰到只剩70%, 就算壽命結束 )。

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