Low watt led are better

[electroyas]

As i understand low watt led are better than high power led with huge heat sinks. For example 10W vs 0.25W led. What do others think about this?

 

[MikeMl]

It takes >40 0.25W LEDs to produce as much light as a single 10W LED. For a given light output (lumens), the total amount of heat produced (losses) using multiple LEDs will be greater.

 

[electroyas]

If the heat power depends on current squared then higher power should be more wast as heat than light right?

 

[electroyas]

What i mean is that I^2*R as heat, then light depends on current I , as i remember

 

[electroyas]

I have a 5W led operating from ac supply, it consists of 1W led in it. But the heat sink gets hot when operating under normal conditions. So whats the point on using 1W for those if they get hot. 1W led i checked seperately still it gets hot under normal operating current. But with smaller led heat is neglegible

 

[dr pepper]

Also depends on the led, luxeon 3 watt leds at least the older ones dont produce the same lumens as 3 x 1w luxeons.

 

[crutschow]

Whether several lower-power LEDs are better than one high-power LED depends upon the luminous efficiency (lumens/watt) of the devices. The one with the higher efficiency is the better.

 

[Toe Cutter]

I think it depends on what you are trying to illuminate and the application. A 0.25W LED might not even need a heat sink, or a very small one. The 10W LED (most likely a module) does need a heat sink. To get the most light, efficiency and lifetime from a LED, they need to be operated well below their maximum temperatures.

I think temperature and power dissipation is an important constraint on commercial LED bulbs. Manufacturers can't make a LED bulb with high light output (and a giant heat sink) for fear of scaring off customers. Fortunately, efficiency is improving all the time.

 

[ronsimpson]

What i mean is that I^2*R as heat, then light depends on current I , as i remember

I think you idea is based on a formula that is not used right.
I agree with light depends on current.
I agree with I^2*R but R is not a constant.
Compare a 1W led and a 2W led. Yes the I=2x but the R=1/2 and the w=2x.
So a 2W led produces 2x the light and 2x the heat not 4x the heat.

 

[ChrisP58]

It all comes down to the ratio of light output to electrical power in. An that has nothing to do with high power or low power, just the ratio.

There are a lot of different LED's out there with different power/output ratios and prices. I don't know if a high power LED (of equivalent semiconductor type) will necessarily be more efficient. But they're probably less expensive overall for the same light output. Meaning that the cost per lumen is probably lower.

 

[electroyas]

Then there is no benifit of using small led to make high power led. Then how can you make high power LED like 10W more effecient? By physical as well as from operating circuit? I heard by increasing voltage and lowering the duty cycle.Is this possible without using traditional dc power?

 

[MrAl]

Hello there,


Lower duty cycle has just the opposite effect: it lowers the efficiency. The highest efficiency you can get is with lower current not higher current even if it is pulsed.
To find out why this is true, you can look at the efficiency curves for a typical LED. What we see is at lower currents the efficiency is nearly a straight line meaning it is nearly constant over a range of low currents. But as the current increases more we start to see the graph curve more and more toward the horizontal, and a horizontal curve means very bad efficiency. So the slope decreases with current too and that means the efficiency is less and less. For example, if you take a normal 20ma LED and run it at 10ma, you get more light output per amp. Since the voltage also comes down, that means higher efficiency. So running TWO of these LEDs at 10ma each produces more light than running ONE of theses LEDs at 20ma. Running FOUR of them at 5ma produces even more light yet, for the same TOTAL current and also the voltage is less so the efficiency goes up even more. The limit to the effectiveness of this is when we get close to the straighter line part of the efficiency curve. Just how much difference it makes though depends on the type of LED.

So there are ways to deal with the efficiency, but they usually are not as simple as we would like to see. Buying more LEDs is the only way to get more efficiency so you can run them at half current, and that may not produce enough extra light anyway.

I have rebuilt one of my lights several times now. As the LEDs get better i have replaced the LED several times. I started with an early Luxeon Star 1 watt, then went to a better one, then to a 3 watt Cree. I run the Cree at less power though not only to get higher efficiency but less heat and longer battery life. I had considered going to a much higher power LED like 10 watt, but the extra heat is just too hard to deal with in a hand held light unless it is a big one and this one is smaller so it would mean total redesign.

 

[kinarfi]

Another consideration is what your trying to accomplish, I've been playing LED lighting from 14.2VDC for some time for the purpose of lighting up the road ahead of me for off road driving and I have found that the 3 watt is the easiest to get lenses for and can be easily grouped. The 10 watt LEDs can be bought with a 60° lens built in, but the 3 watt lens angle can be as low as 5°.

 

[MrAl]

Hi,

Wow, 5 degrees, that's a pretty tight beam. My current light i modify a lot has a 10 degree optic, and that's pretty tight too so i could just imagine how more narrow the 5 degree optic would be. That would be very good for outdoors as i find that the tight beams are good for outdoors and the wider beams are better for normal indoor use in the home. I guess in a theater a tighter beam would be good too because of the longer distances involved. So it seems to go with the distance, the greater the distance the tighter the beam. Now to invent a variable beam angle optic ;-)

 

[dr pepper]

Cant you just adjust the angle by moving the light source in the reflector, or are we talking about a lens?

I'm playing around with the idea of a 10w led as a pushbike headlight, and you can get lenses for them off ebay, not sure what the angle is though.

 

[kinarfi]

For me, I prefer using 3 watt LEDs with either a 3 gang reflectors or single reflector, that's been the easiest and most versitle for me. Here's a bunch of photos of what I have done with 3 watt LEDs https://www.dropbox.com/sh/hjejcldjsdl5cfp/ozB1GLArvo with some other stuff also. Being as I'm using these for automotive, I have found that 4 in series works well and needs no limiting resistor.

 

[throbscottle]

I read recently that it is a well known problem in the LED industry that higher power LED's are less efficient than smaller ones, and no-one really understands why - can't remember where I read it but this article covers it:
https://www.digikey.com/us/en/techz...fying-the-causes-of-led-efficiency-droop.html

So given the choice, it makes sense to use several lower powered LED's than one big one.

Oh, here we go, I found it: https://tech.slashdot.org/story/13/04/23/2332245/cause-of-led-efficiency-droop-finally-revealed seems the researchers understand why now.