Difference between Halogen & LED Low Watt downlights ?

[JohnW2]

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

Yes, I would imagine that. I suppose what I was really asking (at least, in my mind ) is whether anyone was aware of any emerging technologies which might in the future represent a more efficent way of converting electrical energy into light. I believe that some chemico-luminescence and bio-luminescence processes are very efficient - but that, of course, is not a case of converting electrical energy into light - but, if true, that may offer some clues.

I assume that anything approaching 100% efficiency will probably never be possible, since (no matter how generated) some photons are almost bound to hit something, and in the process will presumably result in some energy being converted into something other than visible light.

Kind Regards, John.

 

[sparkticus]

I assume that anything approaching 100% efficiency will probably never be possible, since (no matter how generated) some photons are almost bound to hit something, and in the process will presumably result in some energy being converted into something other than visible light.

Kind Regards, John.

John, that is essentially correct. There are significant LED developments in the pipeline for allowing the escape of more photons and for generating more per total unit energy input.

One recent and ongoing development is "escape cones" engineered into the lattice to allow photons a better opportunity of escape. They look like funnels with the small end at the recombination epicentre.

In terms of efficiency keep in mind that a photon generated in an LED (PN Junction) is essentially a secondary effect. The primary effect of applying a potential difference across the junction is to elevate electrons above the so called fermi-level/vacuum level and up into the conduction band. This consumes more energy than is offered back as a photon (of given wavelength) so it is a "lossy" system by nature but not by much. The major inefficiencies are the poor photon escape statistics. about 70% do not escape as of about 2 years ago. The photon internal collisions and defects in the lattice leading to indirect recombinations in the IR range also contribute greatly to the chaos.

Well, I just got home and now have to walk the lab who is almost sitting on my desk trying to get attention

 

[JohnW2]

In terms of efficiency keep in mind that a photon generated in an LED (PN Junction) is essentially a secondary effect. The primary effect of applying a potential difference across the junction is to elevate electrons above the so called fermi-level/vacuum level and up into the conduction band. This consumes more energy than is offered back as a photon (of given wavelength) so it is a "lossy" system by nature but not by much. The major inefficiencies are the poor photon escape statistics.....

Thanks. The fact that applying voltage across a P-N junction only results in generation of a photon as a secondary effect presumably leaves some hope that an approach which is currently unthought of (and quite probably currently 'unthinkable', just as LEDs once were) will one day provide us with a means of generating photons as a primary effect of applied voltage - although, even then, I presume that photon escape will always be a challenge to be addressed.

Kind Regards,John

 

[sparkticus]

Yes an interesting point. A photon is essentially energy. The amount of energy it represents depends upon its wavelength. A photon from the ultra-violate part of the electromagnetic spectrum carries more energy than a photon from the infra-red. Xrays are very high energy photons with very short wavelengths. Photons in the radio wave part of the spectrum are lower energy (longer wavelength)

Photon energy is related to the frequency X plank's constant.
Or more practically E= planck X speed of light / wavelength
That results in units of Joules/second. If you further divide by the charge on an electron (1.602 X 10^-19) then you get electron volts.

Firing electrons at a tungsten target produces xrays (high energy photons) Photons striking a target liberate electrons. So there is some reciprocation.

It certainly appears that an energy consuming "action" is required to create a photon and it appears to be like lifting a book from the floor to a shelf. The book now has the potential to turn kinetic (if the shelf is removed) but how to get the book there without lifting it? for that matter how to get the "lifter" to lift it without him having his weetabix that morning

 

[sparkticus]

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.

There are several "technologies" of laser diodes but in general (and I am sorry to give a pessimistic answer) they are intrinsically no more efficient than LEDs. In fact they may be slightly less efficient because they get very hot. A semiconductor laser diode is essentially an LED with a very well defined depletion zone where recombinations are concentrated in a smaller area. The resulting highly monochromatic energy in the form of photons are reflected and resonated across the depletion zone influencing a common mode population inversion, in other words most recombinations occur at the same point in time which creates a coherent beam of light (all all photons are in phase with one another) This coherency being the main differentiator between LEDs and laser diodes.