Question: Are LEDS really more efficient than incandescents?

[brightnorm]

In order to power an LED array that would generate the same total amout of light (lumens, candela, peak this or that, I don't know the technical terms, but I think you know what I mean) of say, an E2, would you really need less power than 2x123? Please explain in layman's terms. Thanks

PS I know that batteries too exhaused to power an incandescent can power some LEDS, but I don't believe that really answers my question

Brightnorm

 

[RonM]

Some of the newer LEDs are approaching the efficiency of a halogen bulb. I'm sure others with more experience and knowledge will correct me, but I think a halogen has an efficiency of 18 lumens/watt (or was that 15 lm/w?). So in general, LED flashlights are not more efficient than halogens. That said, I feel they produce "better" light at low power. So a .1W incandescent may look very dim and yellow but a .1W LED might produce nice white light. Hope that helps.

 

[brightnorm]

RonM

That's very helpful and clear. Thanks!

Best regards,
Brightnorm

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by brightnorm:
In order to power an LED array that would generate the same total amout of light (lumens, candela, peak this or that, I don't know the technical terms, but I think you know what I mean) of say, an E2, would you really need less power than 2x123? <HR></BLOCKQUOTE>

As always: Yes and no.

1. When you need coloured light (traffic signal, car's rear lights) LEDs are unbeatable now for several years.

2. For white light it is a little more complicated:

If money is no issue, you may take 500 'S' grade Nichia LEDs (the best one currently) and power them very low. Then you take the most efficient regulator to match the LEDs and drive them very low at 1-2 mA each. Then you will get 25-30lm/W.
If you take the best halogen bulbs and drive them also with a regulator to keep them at the perfect working point and start them soft, you will get also some 25lm/W. You may get more, but then you have a shorter bulb lifetime.
So when using fancy electronics and lots of money, they will have about the same efficiency.
In real life, the E2's bulb will have some 12lm/W and the usually overdriven LEDs some 10lm/W (or maybe a little less) with fresh batteries.
But batteries are only freh for a short time and when they degrade, the incandescent bulbs get worse and worse while LEDs gain in efficiency.
The actual thing is, that all flashlights are bought with fresh batteries (and compared) at the shop, but used most of the time with not so fresh batteries.

3. Again and again: Your lights efficiency depends higly on your application. If you need a small tactical spotlight, a LED light will be of limited use (at least now). You need an incandescent light.
If you use it to light up a walking trail, an ususal LED's light distribution is almost perfect.
If your lighted objects contain lots of brown, yellow, red the incandescent's lower light temperature may improve it's efficiency by far. If they contain 'colder' colours, the LED light shows it's strength.

And the unit of interest is the luminous flux, or the 'amount of light' measured in Lumen. Depending if you put all your Lumen in a small beam or not, you get more Candela or less. It's like a garden hose. Assuming constant water flow (=Lumen) you may put it into a narrow jet or into a wide spray. The amount of water per second stays the same.

 

[lightuser]

nice explanation!

 

[brightnorm]

PeLu

Thanks for one of the best explanations I've ever seen (and understood!)

One last question: What is the difference between lumens and candela. I know you went into this in some detail in a previous post, but if you'd like to add anything further it might clarify it even more. I remember an old grade school explanation of volts and amps: Amps= the "amount" of electricity,
while volts= the "push" or force pumping the amps. Is this accurate, and is there any analogy between this and a discussion of light brightness and efficiency?

Thanks for your help.

Regards,
Brightnorm

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by brightnorm:
What is the difference between lumens and candela.<HR></BLOCKQUOTE>

Let's take the garden hose analogy:

The water flow per second (Liters (or Gallons for the metrically challenged) per second)is the luminous flux in Lumen.

In the following, when I write amount of water, it is always amount of water per second (if anybody cares about that), because the light is not 'stored' at the target like water.

The amount of water per (solid) angle is the luminous intensity or the 'candela rating'.
Don't think about solid angle, just look at at as you have spray your water through a hole 2.5cm (1 inch) diameter 3m away (10 feet). Our candela rating (reading?) is the amount of water we could feed through this hole. Either we have a medium flux, but higly focused (narrow jet) or we have a high flux to get our desired result.
Some people call this candela reading 'a lamps brighness'.

Now we have the third important unit, the Luminance, measured in Lux. Thats the amount of water you get per square meter (foot). Some people call that 'brightness'.
The Luminance depends on two things:
First on your light's candela rating and second on the distance in between your light and the target. Simple: If you move away with your garden hose, your target gets less water. Or you have to 'focus' (=narrow jet) it more to get the same.

As always, it depends on your application: If you just need a distant spot watered and don't care about the rest, you need a highly focused, narrow jet or just plenty of water. If you have enough water, this is no problem. With flashlights, water ~= lumen ~= watts, you have usually to save your water.
If the distance is given, you have to get the necessary candela.

In the first run, you want to know how much water you get for your money (=batteries). That translates into how many lumens for how long with one set of batteries (or one charge). Then you look into the 'transformation' of lumens into candela. That means how much water hits the target. Is the other water spilled around (maybe I want that) or is it lost in the hose+nozzle (not desired in any case, but sometimes unavoidable).

 

[Brock]

Nicely put PuLu.

 

[brightnorm]

PuLu,

Thank you very much for an explanation that even I could (mostly) understand! I must admit that I occasionally feel slightly intimidated by the sheer knowledge and expertise shown by some members of this remarkable and very special forum. I'm considered an "expert" in my own (non-technical) field, and this is has been quite an experience for me
because, somewhat to my own surprise, I have been really drawn to this subject and this forum where I am a genuinely ignorant novice. (Is there another kind?)

Because of my unlucky background in math and physics (flunked Elementary Algebra in Jr High with one of the lowest averages ever recorded in that school!) I suppose it shouldn't surprise me that now, surrounded by savvy "Technophiles" and "Mathophiles", I feel a little out of my depth. I'm also aware that there are LEO, security and military people in this forum whose daily use and evaluation of these products has a critical relevance in their lives.

I will console myself in the knowledge that I, as a layman can buy and evaluate products on my own terms,in a way that may be of some interest and usefulness to others, and that by asking questions I can improve my own knowledge, share this knowledge with others, and continue to participate as a member of a group that I have come to appreciate and respect.

Very best regards from
Brightnorm

 

[lightuser]

Wait till you get our monthly bill! (joke)

 

[L.E.D.]

incandescents 'R' us

LIFE
LED: operating life: 11 years if not overdriven(most flashlight packages R lying sacs of undigestible protein matter and tell you the 11 year operating life, but they overdrive it)

Incandescent: Maybe 3 yrs at the most if you're lucky.

PHYSICAL STRENGTH
LED: just about unbreakable, unless you take a hammer to it.

Incandescent: A shockwave from my fart could destroy an incandescent.(filaments suck)

BRIGHTNESS -poor LEDS, this is where u lose, 4 now-
LED: bright enough for a walking light, but not for overwhelming sometinhg's optic nerve

Incandescent: one word: OUCH

COLOR
LED: pretty pure white Light!!

Incandescent: wow, the wavelength of the photons coming out of your "whiter krypton bulb" remind me of the wavelength of the photons reflected off of my vomit.

LED's are overall better, I'd say, unless you're trying to burn someone's eye out.

 

[L.E.D.]

by the way, I usually have yellow vomit. LOL

 

[Darell]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ledfreak:

by the way, I usually have yellow vomit. LOL<HR></BLOCKQUOTE>

Ah, that clears it up.