Difference between Halogen & LED Low Watt downlights ?

[riveralt]

Most of the forward biased current does not contribute to usable emitted light. So an LED is not that efficient at producing light in absolute terms but is vastly more efficient than incandescent lamps etc.

Nor do they not produce heat.

They might not produce infrared radiation like an incandescent lamp but they certainly produce heat and hence need some form of efficient thermal management - normally in the form of a heat sink.

http://www.ledsmagazine.com/features/2/5/8

 

[sparkticus]

Hmmm - some pretty fundamental laws of physics are at risk of being violated here If most of the energy utilised does not end up as light or heat (and I don't think LEDs are very noisy, or do any mechanical work) ...... ????

Remember that an LED is a 3 dimensional structure crystal lattice (A thin film PN junction) It is unlikely that all photons generated in recombination will escape to the outside world. In fact most do not. They strike internal structures and behave "statistical" manner after that (and indeed before that)

LEDs (and most semiconductor devices are quite noisy, electrically speaking. They also move (or vibrate) under stimulus (acoustic phonon behaviour)

 

[sparkticus]

They might not produce infrared radiation like an incandescent lamp but they certainly produce heat and hence need some form of efficient thermal management - normally in the form of a heat sink.

They do produce infrared energy. two major factors:

1) the forward bias current: electrons colliding in a low mean free path environment.

2) many of the recombinations result in an indirect transition which results in low energy (relatively speaking) which is longer wavelength than the desired light output which results in heat generated. This also happens in direct band-gap materials such as silicon in standard diodes/transistors etc. In fact standar silicon devices generate light (photons) but always at about 1.1 microns (near infra red)

 

[sparkticus]

I should add that I was only talking about the specific device physics of the LED process.

In practice a mains halogen LED replacement (for example) will generate much of its heat from the electronics housed in the neck of the glass envelop.

 

[ericmark]

Wops missed the date.

 

[ban-all-sheds]

I'm gobsmacked that 3 people didn't read properly

NOR

do

they

NOT

produce

heat.

 

[sparkticus]

I'm gobsmacked that 3 people didn't read properly

NOR

do

they

NOT

produce

heat.

No, No BAS, I got that. I was agreeing with you. In other words you said they do produce heat.

 

[sparkticus]

I'm gobsmacked that 3 people didn't read properly

NOR

do

they

NOT

produce

heat.

No, No BAS, I got that. I was agreeing with you. In other words you said they do produce heat.

PS I see you speak combinational logic

 

[sparkticus]

[quote="ban-all-sheds";p="2032400"
Electron stimulated luminescence lamps look interesting.[/quote]

Oh yes, very interesting. I have not really seen these in the field (or not noticed them) They work by heating a cathode and accelerating electrons at a phosphorescent inner surface just like a CRT tube. In fact if you modulated the cathode bias and added a deflector coil you could have little animated patterns and even images on your light bulbs. Should we file a patent?

 

[JohnW2]

I'm gobsmacked that 3 people didn't read properly

Ah well, at least I'm in good company My apologies.

Just as well I don't speak Boolean on Sundays, otherwise I might intrepret nor...not as 'or'!

Kind Regards, John.

 

[ban-all-sheds]

No, No BAS, I got that. I was agreeing with you. In other words you said they do produce heat.

Oh well - I hope people enjoyed the irony I provided.

So that'll be 2 people who didn't read what I wrote, and one person who didn't read what a 3rd wrote.

 

[JohnW2]

OK - so roughly what are the efficiencies (in terms of electricity to light conversion) of LEDs, discharge tubes and incandescents - anyone?

Kind Regards, John.

 

[ban-all-sheds]

http://donklipstein.com/light.html

 

[JohnW2]

• http://donklipstein.com/light.html

Thanks. Looking at a small sample of the links there seems to suggest that current (white) LEDs are generally slightly more efficient than CFLs and that (as one might expect), both of them are probably 4-6 times more efficient than incandescents.

I must admit that I would have guessed a bigger difference between LEDs and CFLs, but the use of LEDs for serious lighting is in its relative infacncy, so one might expect that developments will result in appreciable improvements in efficiency.

Any physicists or academic engineers out there? I was wondering what is the most efficient currently known process for converting electricity into light.

Kind REgards, John.

 

[echoes]

I was wondering what is the most efficient currently known process for converting electricity into light.

No good for a reading by, but a semiconductor laser should be more efficient than an LED in terms of power out/power in.