# What is the definition of an efficient light bulb? Less heat and more light..Right?



## HighlanderNorth (Sep 22, 2011)

Long ago I watched a tv show about lighting technology, and what they kept coming back to was that inefficient lights waste energy by producing heat, and less actual light. For instance, they mentioned that fluorescent tubes were MUCH more efficient than incandescent bulbs because they produce lots of light at lower power levels without the heat, by running cool, which means that, by definition, they are more efficient.....Because they arent wasting their energy on unnecessary and unwanted heat production.

But then, years later, I hear how efficient HID lighting is, and I eventually buy an HID light, a 400w MH. But the dealer who sold it to me warned me about all the HEAT that it would produce, but he said it was very efficient....... That comment made as much sense to me as if he'd said, "my daughter makes good grades, she makes all F's"

So.......whatever happened to "efficiency means less heat production, more light , and a cool running bulb?"

Then I start getting into LEDs recently, and I immediately begin hearing people saying things like "LEDs produce LOTS of heat, and need a good heatsink to draw away all that heat".... Followed by "Leds are SOOOOO efficient!" Again....."My daughter makes good grades, she makes all F's"

When we are NOW talking about light bulb efficiency, are we actually talking about their ability to 'efficiently' heat a small room, or to efficiently make light?

I'm confused........:thinking::thinking::thinking:

Also, I saw someone mention that fluorescent tube fixtures are old and outdated... But what about their ability to produce good light with less energy and almost no heat?

Apparently I've got a lot to learn here, and I MUST have been misinformed years ago when originally watched these tv documentaries on lighting efficiency.......


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## MikeAusC (Sep 22, 2011)

Even the best LEDs today waste 80% of the electrical input as heat - but it's still better than filament bulbs.


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## SemiMan (Sep 22, 2011)

MikeAusC said:


> Even the best LEDs today waste 80% of the electrical input as heat - but it's still better than filament bulbs.


 
Actually the best blue's waste about 50% and the best whites somewhere around 35-40%.

Semiman


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## jtr1962 (Sep 22, 2011)

What's missing from the equation is _surface area_. Operating temperature has little to do with how efficient something is. For example, the best white LEDs are more efficient than the best linear fluorescent tubes. The fluorescent tubes may not get as hot as the LEDs simply because they have a much greater surface area over which to dissipate their heat. For similar reasons, CFLs get much hotter than linear tubes even though in some cases they're nearly as efficient. If you had an LED fixture producing the same amount of light as a linear tube fixture, and with the same surface area, it would be quite a bit cooler.

Bottom line-if you want to use operating temperature as a barometer for efficiency, then you can only compare equally sized fixtures producing equal amounts of light. If you do that, the more efficient fixture will always be cooler.


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## blasterman (Sep 23, 2011)

Halides get too much bad press when it comes the thermal issues. A state of the art fluorescent fixture throws about as much thermal as an equivelant halide at the same wattage. The difference is the halide produces it in a tiny area.

Funny that when I recently retrofitted some 300watt halogen fixtures with 75watt halides one old timer electrician watching was concerned about the "additional energy consumption and heat produced because it was halide."

:laughing:


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## Steve K (Sep 23, 2011)

SemiMan said:


> Actually the best blue's waste about 50% and the best whites somewhere around 35-40%.
> 
> Semiman


 
that's a lot better than I had thought.... where does that data come from?

thanks,
Steve K.


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## SemiMan (Sep 23, 2011)

Steve K said:


> that's a lot better than I had thought.... where does that data come from?
> 
> thanks,
> Steve K.


 
Top bin Cree XML at 350mA (and the underlying blue die)


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## Steve K (Sep 23, 2011)

SemiMan said:


> Top bin Cree XML at 350mA (and the underlying blue die)


 
but where did the data come from? i.e. the datasheet? I'm looking through rev 2 of the datasheet and can't find anything related to optical power out per electrical power in. Page 2 mentions up to 280 lumens at 700mA.... and later on page 2 they say that Vf @ 700mA is 2.9v typical, so at least you know that you're getting 138 lumens per watt. Is there a conversion for lumens to watts?
The wiki page for lux mentions that with green (555nm) light, the conversion is 683 lumens per watt, but doesn't mention the fudge factor for blue light (other than to say that it is different and smaller). The wiki page for luminous efficacy hints at more details, but I can't seem to find the solution there either.

Steve K.


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## slebans (Sep 23, 2011)

Steve K said:


> but where did the data come from? i.e. the datasheet? I'm looking through rev 2 of the datasheet and can't find anything related to optical power out per electrical power in. Page 2 mentions up to 280 lumens at 700mA.... and later on page 2 they say that Vf @ 700mA is 2.9v typical, so at least you know that you're getting 138 lumens per watt. Is there a conversion for lumens to watts?
> The wiki page for lux mentions that with green (555nm) light, the conversion is 683 lumens per watt, but doesn't mention the fudge factor for blue light (other than to say that it is different and smaller). The wiki page for luminous efficacy hints at more details, but I can't seem to find the solution there either.
> 
> Steve K.


 
While you are waiting for SemiMan to reply you might want to take 15 minutes and skim through this thread. It will give you some background on this issue.
http://www.candlepowerforums.com/vb/showthread.php?311740-LEDs-waste-75-as-heat

Stephen Lebans


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## idleprocess (Sep 23, 2011)

Efficiency is more or less defined as "amount of useful energy you get *out* of a system relative to how much you put *into* it."

For electrical light sources, the metric is generally lumens per watt (Lm/W). The use of the lumen (as opposed to an electrical unit such as the _radiated_ watt) is important since it only measures visible light. EM emissions outside of the visible spectrum are considered waste for general-purpose light fixtures. In some niche applications, waste light in the form or IR or UV is useful, but for general-purpose lighting it's generally of no use.

I suppose that the proper term I'm looking for is "luminous efficacy" since Lm/W is a narrower term than "efficiency."


Incandescents do indeed waste most of their energy producing heat ... small wonder since their method of action involves heating a filament to just-above melting. The typical cheap incandescent lamp in the 40-120W range averages 10-20 lumens per watt. Halogen incandescents do marginally better.
Florescents do much better: CFL's are anywhere from 30-60 lw/W; T8 floros are typically over 80 lm/W.
LED bulbs - currently in their infancy and shoehorn compromise designs - are pushing 50 lm/W. LED's in more cutting-edge devices (such as flashlights) are pushing 100 lumens per watt. I remember hearing that LED's in the lab are beating 150 Lm/W.
Metal Halide bulbs are often 90 Lm/W
High Pressure Sodium bulbs are typically >100 Lm/W

The great thing about LED's is that the spectrum they emit (from the die, anyway) is quite narrow. White LED's (really just blue LED's with a phosphor coating that converts some of the blue light into a wider spectrum with a read peak) emit light almost 100% within the visible range.

LED's do indeed produce heat since they're devices with imperfect efficiency _(like everything!)_. Unlike the other technologies listed, they are considerably less immune to the effects of heat, nor do they radiate it directly... thus they get hot during operation and must have said heat removed before they overheat.


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## SemiMan (Sep 23, 2011)

Steve K said:


> but where did the data come from? i.e. the datasheet? I'm looking through rev 2 of the datasheet and can't find anything related to optical power out per electrical power in. Page 2 mentions up to 280 lumens at 700mA.... and later on page 2 they say that Vf @ 700mA is 2.9v typical, so at least you know that you're getting 138 lumens per watt. Is there a conversion for lumens to watts?
> The wiki page for lux mentions that with green (555nm) light, the conversion is 683 lumens per watt, but doesn't mention the fudge factor for blue light (other than to say that it is different and smaller). The wiki page for luminous efficacy hints at more details, but I can't seem to find the solution there either.
> 
> Steve K.


 
Good rule of thumb is 300 lumens/optical watt for YAG phosphor converted LEDS. Range is likely 280-315. Do the math from there.

Below is the data on Luxeon Rebel (and ES) royal blue. Cree XML is about 10% more efficient ... and these numbers below are at 700mA. At 350 add another 10-15% so blue efficiency with a cool die is up to 60% at 350mA if my math is correct but bring that back down to 55% for a warm die.


art Min Radiometric Power
(Royal-blue is specified in mW) Typical
WPE Typ Radiometric Power Min
Wavelength Max
Wavelength
LXML-PR01-0500 500 mW @ 350 mA 48% 910 mW @ 700 mA 440 nm 460 nm
LXML-PR01-0425 425 mW @ 350 mA 44% 840 mW @ 700 mA 440 nm 460 nm
LXML-PR02-1100* 1100 mW @ 700 mA 53% 1120 mW @ 700 mA 440 nm 460 nm
LXML-PR02-1000* 1000 mW @ 700 mA 49% 1030 mW @ 700 mA 440 nm 460 nm
LXML-PR02-0900* 900 mW @ 700 mA 46% 970 mW @ 700 mA 440 nm 460 nm
LXML-PR02-0800* 800 mW @ 700 mA 42% 890 mW @ 700 mA 440 nm 460 nm


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