They are Crappy becuase they are engineered to be crappy. Read on.
Over the last few years I have noticed that I can’t find compact fluorescent (spiral / curly q) light bulbs at the store I shop at (in California). Almost all of the incandescent light bulbs are gone too. I knew this was going to happen and I was looking forward to buying light LED light bulbs that would last 5 years or more of continuous use. Many LEDs (the actual component emitters) have a rated life span of 50,000 hours or more if operated at a specified current (amps/ milliamps).
So as I write this, I am looking at the box of two 60 watt equivalent LED light bulbs I purchased that are each rated at 10 years life. Oh joy. Wait…. Then it says “Based on 3 hours a day”. That works out to about 11,000 hours of continuous use. What happened to the other 40,000 hours? Well, these light bulbs run kind of hot for LEDS. My guess is that they are running the LED emmiters at a higher current than optimum for a normal 50,000 hour lifespan. The operating current may be below the absolute maximum current rating specified by the manufacturer but running at a higher than optimum current will take its toll in the form a reduced life, lower efficiency, and excessive heat. On a positive note, when some manufacturer does make and market a 50,000 hour bulb they can say it lasts 40 years based on 3 hours a day.
But back to this 2 pack of LED light bulbs I bought. Do you think the manufacturer of these bulbs knows about 50,000 hour LEDS? Do they know how to engineer a light bulb that runs the LEDs within specs to last 50,000 hours? This company should. These are name brand light bulbs and the named company on the box is the same company that manufactures or at least puts their name on reels of component LEDS. I suppose there is a point from the manufacturer’s perspective to selling a consumer product that does not last very long.
I removed the translucent plastic round part of one of the lights to find 10 tiny surface mount LEDS. I measured about 60 volts powering the 10 Leds so potentially the voltage across each LED could be 6 volts. There may be a resistor in the circuit as well but I did not see one. This light is rated at 8.5 watts and 800 lumens. This works out to less than 100 lumens per watt. This is crappy efficiency. Surface mount LEDS of the type in this lamp are available with lumens per watt ratings of 150 to over 200. The efficiency of LEDS goes down as the current running through the device goes up. The heat goes up as well. My guess is that the product was designed for a low part count and low operating life. While the lumens per watt rating looks good when making a comparison to a Fluorescent bulb (almost twice as efficient) it is awful in regard to the efficiencies of the redilily available components when properly engineered into a product.
The operating forward voltage rating for LEDS is typically a very small range going from no light being produced to burning out right a way. The range is so narrow that a 10 to 20 percent change makes a huge difference in the operating characteristics of the product. In the case of this light bulb. having 11 or 12 LEDS in series instead of 10 at the same 60 volts would probably be all that is needed to turn a marginal product into a quality product. Perhaps this light bulb could have been a 5 watt replacement for a 75 watt bulb that would easily last 3 or 4 times as long as this one.
I spent a few hours over the last couple of weeks looking at specifications for different LED emitters. I even bought some to play around with. I found some manufactured by the company that made the light bulbs which had excellent specifications. I almost bought some of them but settled on Samsung LEDs instead. After I ordered and received my LEDS I ran across the LH351B series of LEDS. These are higher power devices than what I typically experiment with. I have made and re-engineered flashlights that run in some cases hundreds of hours on a set of D cell batteries and this series of LEDS is not ideal for that type of application but perfect for high efficiency residential and commercial lighting applications. I am so impressed with the specs that I may buy 10 from Digikey next week. It will be interesting to see how much light I can get out of 10 to 20 milliamps. Here is a link to an article about the LH351B series:
The efficiency is 173 lumens per watt at 350 ma. It is easy to find lower power devices with higher Lumens per watt ratings. 173 Lumens per watt at 350 ma is excellent.
- the article: Samsung’s LH351B has an expected lifetime of 280,000 hours at 105°C, 1A. Let me interpret that. Even if you run this device at almost 3 times the current rating to achieve 173 lumens per watt, this device should run continuously for 280,000 hours (and the LED will be too hot to touch). Amazing. 5 of these running at 350 ma would make a fine 5 watt (about 5 watts, The power supply that converts 120 volts ac to a lower DC voltage requires a little power too) 800 plus lumen light bulb that should last for over 30 years of continuous use. Since I don’t run any light more than 12 hours a day I will be looking forward to not needing to replace these for about 60 years. I suppose it could be marketed like this: “Life: 240 years based on 3 hours a day”.
OK. Lets talk crappy internal combustion engine designs…..
About the author: Wirkbot is a geek. He works somewhere doing something but when he is not working is working at being a geek.
Flashlight with over 300 hour run time:
Uses for dead car batteries:
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