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LED Industry Innovations: 6 Trends to Follow
3/19/2014

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Light-emitting diodes have been around for 50 years, but they have only developed to the point of being suitable for general-purpose lighting in the last 10. The field is undergoing rapid evolution mapped by the LED equivalent of Moore's Law.
 This is Haitz's Law, and it states that in every decade, the cost per lumen (unit of useful light emitted) falls by a factor of 10, and the amount of light generated per LED package increases by a factor of 20 for a given wavelength of light.

If LEDs are to be used as a source for lighting, more is involved than the LED dice themselves. An LED-powered lamp or luminaire (i.e., fixture) requires phosphors, optics, a heat sink for thermal management, and driver electronics, as well as packaging for all of these parts. The worldwide switchover to LED lighting, replacing the woefully inefficient incandescent technology, is driving rapid improvements in all of these areas. Prices for LED lighting products, once astronomical, are falling into the range of feasibility.

Essentially all of the LEDs used in lighting are based on the semiconductor gallium nitride, GaN. This is bonded to a substrate, which in the majority of LEDs today is either sapphire or silicon carbide. Other substrates are under development, as we'll see below.

LEDs are inherently more versatile and potentially far more efficient than any other light source yet devised. An incandescent filament source has a 'luminous efficacy' of around 15 lumens of light for every Watt of electricity input. The rest is wasted as heat. Fluorescents typically run in the range from 45 to 75 lm/W. Metal halide achieves up to 115 lm/W and high-pressure sodium up to 150 lm/W. LEDs can theoretically achieve a maximum of between 260 and 300 lm/W. Current commercial examples run in the high 100s, and the numbers are rising every year.

All LEDs produce heat, but they don't radiate it out the front with the light. They accumulate it at the p-n junction, and the heat has to be removed if an LED is to achieve its designed lifetime. This is accomplished with the aid of a heat sink and a known thermal path to ambient.

LEDs produce light in proportion to the current flowing through them, and most are fed by a DC power supply and a driver circuit that holds the current constant. Early experimentation with driving LEDs directly from AC line current has matured, and AC drivers for LEDs, with their simpler circuitry and lower component count, are claiming a place at the table.

The versatility of LEDs leads to explorations of what they can do for us besides producing white light. Our understanding of the effects of light on humans (and other living things) is increasing rapidly. LED lighting is being asked to contribute to human health, well-being, alertness, attention, the food supply, and more.

Light-emitting diodes have been around for 50 years, but they have only developed to the point of being suitable for general-purpose lighting in the last 10. The field is undergoing rapid evolution mapped by the LED equivalent of Moore's Law.

This is Haitz's Law, and it states that in every decade, the cost per lumen (unit of useful light emitted) falls by a factor of 10, and the amount of light generated per LED package increases by a factor of 20 for a given wavelength of light.

If LEDs are to be used as a source for lighting, more is involved than the LED dice themselves. An LED-powered lamp or luminaire (i.e., fixture) requires phosphors, optics, a heat sink for thermal management, and driver electronics, as well as packaging for all of these parts. The worldwide switchover to LED lighting, replacing the woefully inefficient incandescent technology, is driving rapid improvements in all of these areas. Prices for LED lighting products, once astronomical, are falling into the range of feasibility.

Essentially all of the LEDs used in lighting are based on the semiconductor gallium nitride, GaN. This is bonded to a substrate, which in the majority of LEDs today is either sapphire or silicon carbide. Other substrates are under development, as we'll see below.

LEDs are inherently more versatile and potentially far more efficient than any other light source yet devised. An incandescent filament source has a "luminous efficacy" of around 15 lumens of light for every Watt of electricity input. The rest is wasted as heat. Fluorescents typically run in the range from 45 to 75 lm/W. Metal halide achieves up to 115 lm/W and high-pressure sodium up to 150 lm/W. LEDs can theoretically achieve a maximum of between 260 and 300 lm/W. Current commercial examples run in the high 100s, and the numbers are rising every year.

All LEDs produce heat, but they don't radiate it out the front with the light. They accumulate it at the p-n junction, and the heat has to be removed if an LED is to achieve its designed lifetime. This is accomplished with the aid of a heat sink and a known thermal path to ambient.

LEDs produce light in proportion to the current flowing through them, and most are fed by a DC power supply and a driver circuit that holds the current constant. Early experimentation with driving LEDs directly from AC line current has matured, and AC drivers for LEDs, with their simpler circuitry and lower component count, are claiming a place at the table.

The versatility of LEDs leads to explorations of what they can do for us besides producing white light. Our understanding of the effects of light on humans (and other living things) is increasing rapidly. LED lighting is being asked to contribute to human health, well-being, alertness, attention, the food supply, and more.

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AZskibum
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Re: Great summary and lots more info at
AZskibum   3/23/2014 11:01:26 PM
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"most illuminating discussions", LOL! Thanks DrFPGA, I will check it out.

LarryM99
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CEO
Re: Great summary and lots more info at
LarryM99   3/23/2014 7:49:21 PM
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You are right, it is an interesting site. I knew that there had to be somewhere where they were pushing the limits and doing interesting things with LEDs, and this is a good example of that. Thanks much for the reference!

DrFPGA
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Great summary and lots more info at
DrFPGA   3/23/2014 6:11:19 PM
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http://www.allledlighting.com 

If you are interested in what's going on in the world of LED Lighting follow Keith and his trusty minions at www.allledlighting.com for some the the most illuminating discussions on the good, bad and ugly in the LED lighting market.

You will be amazed at the brain power that explodes daily from the site... Really!

AZskibum
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CEO
Re: LED's and Color
AZskibum   3/23/2014 10:37:14 AM
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Excellent point. A big factor in my motivation to transition my home lighting from CFL to LED (still a work in progress) was the color of the white LED light. The lights I bought did not specify CRI, only color temperature, but in any case they were a huge improvement over the horrible greenish hue of the CFLs.

_hm
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The Best Light Source?
_hm   3/22/2014 6:53:00 AM
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"and a versatility in the spectrum and character of light beyond that offered by any other source that humans have yet discovered or invented."

Really? CRI for LEDs are pretty poor 95 or 96 at best. How do justify this?

baybal
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Rookie
Re: Silicon substrate
baybal   3/21/2014 4:15:11 PM
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No,

Why? It is impossible to put an efficient capacitor or inductor on silicon yet. It is possible however to put other non-conversion related components like dimming.

Even if somebody will manage to make a self-driving chip with high step-down, it will be inefficient in comparison to dedicated driver.

In addition to that, most of led products nowadays are using LEDs in multi-chip modules, in which a lot of cheap blue leds are bundled instead of single, high current one.

GeniusEE
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Freelancer
Re: LED's and Color
GeniusEE   3/21/2014 12:13:16 AM
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Motherhood and apple pie

"Best" is worthless in a commodity, non-luxury, market, where good enough is good enough

High CRI means low efficacy. The name of the game with LEDs should be energy use reduction, not spec idealism that poisons the environment.

What held back CFLs initially was that they were expensive.

BitHead77
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Silicon substrate
BitHead77   3/20/2014 6:47:23 PM
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Wouldn't the use of a silicon substrate also allow some of the drive electronics to be built along side the LED(s) that is(are) being driven?  Could this be used to reduce cost as well?

Bob Marso
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LED's and Color
Bob Marso   3/20/2014 1:13:08 PM
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One performance specification that held back CFL's acceptance was their poor ability to correctly illunimate the full spectrum of color in our houses.  Our spouses fought CFL's in the living room because they made the living room look like it had jaundice or some liver disease.  LED's are capable of overcoming this - after all the most accurate color rendering of computer images is obtained on LED backlite displays, not florescent backlite displays.

Knowing the color temperature of a light source (measured in degrees Kelvin) is not sufficient to select a good light bulb. The measurement of how wide a color spectrum a light source can accurately display or illuminate is the Color Rendering Index, or, CRI.  The closer to 100 you get, the better the light source.  CRI's in the low 90's are considered the minimum for good color illumination.  I'd like to see all manufacturers of interior lighting sources, no matter what kind, required to specify the color temperature and CRI on their packaging.  This would allow we the consumers to select the best light source and also up the competition among manufacturers to produce a better product.

GeniusEE
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Freelancer
Re: Supply frequency
GeniusEE   3/20/2014 6:27:22 AM
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prabhakar_deosthali   3/20/2014 3:53:02 AM: "Does it really now matter at what frequency the grid electricty is supplied? May be I am missing something!"

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You might want to revisit your freshman year AC Machines class notes

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