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  • "low current"
  • "high efficiency"
  • "high intensity"
  • ... ?

I read these terms in various places and every single time the LED's are just used as a signaling LED in a small circuit, requiring only a few milliamps to light up.

What is the difference? Or is it just marketing speech from different manufacturers?

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"Low current" LEDs would be my product of choice for indicator LEDs in small circuits - Why waste current if less is more? :-) –  Anindo Ghosh Nov 21 '12 at 18:19
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2 Answers 2

up vote 5 down vote accepted

The terms listed do have relevance, albeit limited: There are no globally mandated benchmarks, I believe, for what constitutes low current, or high intensity in an LED.

In general, "middle-of-the-road" LEDs are usually specified at 20 to 25 mA. Thus, an LED that glows at nominally "full" intensity at 5 mA (maybe even 10) would be considered low current.

Over successive generations of LED technology, the luminosity per Watt for LEDs has increased steadily - to the extent that "Haitz's law" observes that light generated per LED in each color increases by a factor of 20 per decade. Some manufacturers market their 100 Lumen/Watt and better LEDs (post 2010) as "High intensity", but that too is clearly a moving target.

High efficiency in LEDs - (warning, moving fully into speculation-space) would be a measure of the light generated in ratio to wasted heat - Of special significance for large high-current LEDs as used in lighting fixtures, where significant design effort goes into cooling / heat-sinking design for the LEDs. Higher the efficiency, lower would be the cooling cost per lumen of light. Where does one draw the border on this? The marketing folks would have to say.

In summary: Until global standardization of these terms, and compliance with such standards, this is essentially marketing-speak.

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One major problem with these kind of phrases that you almost touch on, is that data sheets tend to remain unchanged even as technology moves on. So a datasheet for a part introduced 10 years ago might still say the LED is "high intensity" even if newer parts are even better. Then you get data sheet escalation: "intense", "high intensity" "ultra high intensity" "mega ultra high intensity"... –  The Photon Nov 21 '12 at 18:30
    
@ThePhoton Totally agreed. I'm waiting for Cree to announce a Supernova LED one of these years :-) –  Anindo Ghosh Nov 21 '12 at 18:34
    
Not really a big deal when you're looking for an LED. But when you're looking for a "low noise" op-amp or a "high speed" digital logic family... –  The Photon Nov 21 '12 at 18:43
    
people sell Supernova LEDs today are "high" on brightness and things that grow under them. –  Tony Stewart Nov 22 '12 at 21:13
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The modern LED that uses transparent substrates with back reflectors and AlGaAs AlInP type materials are classified as HB types or high brightness.

"High Intensity" is simply a marketting term. You can get light out of any LED with a few mA and get much more light with a power module than a 5mm LED with 3mA but that is not really cost effective. Power Modules tend to have wide beam angle and for "Indicators" vs Luminators" the low current LEDs have narrow beamwidths as low as 6 deg. for more "brightness" when viewed on center axis although power level is very low. ( < 75mW)

Physical classifications more often used are; Discrete, HB and "Power modules" Packaging styles vary by the hundreds. Current ranges vary from 10mA to 10Amp for arrays. Lumen power depends on input power and substrate efficacy, while Brightness can be modified with reflector lens (cups) built-in which can increase the Luminous Intensity , Iv, "almost" double by reducing the beam angle by 50% until lens losses overcome the gain.

"Low Current" I presume means these are indicators and generally rated at the "de facto" 20mA standard, which by the way is limited by the heat dissipation from epoxy encapsolation which protects it but unfortunately is a thermal insulator.

Higher Current discrete parts have an improved lead frame for better dissipation of heat and can handle 50~100mA. enter image description here

Power Modules are built on Aluminum substrates for better heat spreading and are rated for 0.5W, 1W 3W 5W,10W 50W 100W etc. and may be single junctions or arrays of junctions. Since voltage varies with internal junction temperature, they are generated tested on a cold sink @25'C at constant current.

You can achieve > 200 Lm/Watt at low currents today, but at a high cost/Lumen factor so demand is to increase Lumens/$ at a standard CRI , colour temp and rated power level.

There are many factors which increase Lm/Watt in your choices of existing production LEDs;

example of Sensitivity factor;

S(ζ/If)= -20% ... efficacy,ζ, increases 2% for a 10% drop in If ( & visa versa)

Here are some experience based Sensitivity factors.

  • reduce the drive current S( ζ / If ) = -20% ( lowers ESR losses)
  • increase the Colour Temp S( ζ / 1000'K ) = +6% /1000'K ( less phosphor )
  • pay for higher binned ranges S ( ζ / %$ ) = 100%

    ( pay 2x as much for lumen bins avail with 2x output)

enter image description here enter image description here

The above graph shows the range of Lumens for different part numbers at a fixed colour temperature for the OSRAM LUW CQAR LED.. This part is intended for "streetwhite" colour and not simply warm or cool. 5500'K is considered daylight avearge white. The reason efficacy improves with cool LED's is simply there is less phosphor coating and conversion loss.

Other negative factors for efficacy are; - use poor heatsink thermal resistance and operate much higher than rated 25'C test - exceeding -5V from E fields or staic - excess soldering temps - over-drive the current with PWM peaks to achieve constant average intensity - mfg choice of wafers, reflectors, lens, coatings and manufacturing processes are all significant variables beyond the scope of this answer,.

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Hmm... "efficacy is about the results, whereas efficiency is about waste when achieving the results."(ref) I think you mean efficiency in the last two paragraphs? –  JYelton Nov 22 '12 at 20:18
    
no but thanks, I meant efficacy in all cases. "In lighting design, "efficacy" refers to the amount of light (luminous flux) produced by a lamp (a lamp or other light source), usually measured in lumens, as a ratio of the amount of power consumed to produce it, usually measured in watts. This is not to be confused with efficiency which is always a dimensionless ratio of output divided by input which for lighting relates to the watts of visible power as a fraction of the power consumed in watts." (wiki) –  Tony Stewart Nov 22 '12 at 20:58
    
Ah, I see. Thanks for clearing that up; I should researched the definitions more thoroughly. –  JYelton Nov 22 '12 at 21:15
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