Thoughts on the recent history of illumination

Discussion in 'General Science & Technology' started by billvon, Jun 15, 2023.

  1. billvon Valued Senior Member

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    I first got interested in illumination when I was around 12. I built a light with AA batteries and an incandescent bulb inside a round plastic box. I also had a mercury switch in it, so when I rolled it across the floor it would flash on and off. At night it lit up the room. But during the day I could barely see it. How did that work? How did a bright light become dim just because there was other light there? How do you make as much _useful_ light as possible with as little energy as possible? Because incandescent bulbs were terrible in that respect.

    In high school I discovered LEDs and how efficient they were. At that point they still weren't as good as flourescent light but they were so much easier to use. I built all sorts of things full of flashing LEDs because I thought they looked cool.

    In college I finally got my hands on some very efficient red LEDs, and I built a red flashlight on top of a 9 volt battery. It was remarkably useful; both bright and small enough to fit in a pocket. It was the first time I realized that LEDs could be used for illumination.

    But back then you could get efficient red LEDs and sort of efficient green LED's. Together they made a yellowish light. Everyone who worked with LED's knew that the holy grail was a blue LED - a red, green and blue LED could both make white light and any color humans could see by adjusting their intensities. It was how TV's worked, except they used phosphors. We knew that once you had blue LEDs you could make huge and fairly cheap TVs by using LEDs instead of CRTs. And you could make white lights.

    Around 1990 I found my first blue LED from a surplus place called Hosfelt Electronics. It was a dim not-very-efficient blue LED in a T 1-3/4 housing, but it was absolutely blue and it meant that better ones were coming. I built several "any-color" lights that I could adjust to make any color from warm white to cool white to purple etc.

    In 1992 I was working on flourescent ballasts at work and put together the most efficent ballast plus bulbs I could find. They were high color rendering 34W tubes from Philips, and they put out a lot of light. And it wasn't the usual cold flourescent light either; it was a warmish white that looked a lot like incandescent light. I used it for a light over my workbench.

    The ballast was one of the first Advance electronic ballasts as well. Not only was it more efficient, it was dimmable down to 20% - so I could cut back even further on power when I didn't need it to be bright over the workbench.

    I also started to see compact flourescents start to replace incandescents. They had all sorts of problems - long warm up times, harder to dispose of, some were noisy - but they were a solid 4x improvement in efficiency over incandescents. This was an even bigger deal in warm climates, since air conditioners also had to shoulder the load to cool the incandescents in houses that used them. I changed all the lights in my parent's house out to CFs and they saw a significant drop in their power bill.

    In 1995 I started to get more efficient blue LEDs and made a few white-light flashlights. Then around 2000 blue LEDs with phosphor backings started to appear. These flouresced red and yellow and thus made the light appear white, at a small loss in efficiency (since you lose energy when you downshift in frequency.) But overall they were more efficient than even compact flourescents, and today they are both cheaper and more efficient than CF's ever were.

    Nowadays there are amazingly good high intensity LEDs. Petco Park just replaced all their stadium lights with LED's - so now they can be part of the light show, with their instant on/off times. You can buy light tiles you just stick to your wall that gives you not only white light, but any color light you want. We are continually developing illumination that gives us more light, light that looks better, light with more flexibility - and for ever decreasing costs and ever improving efficiencies.

    And on my wall there is a TV that is made of millions of red, green and blue organic LEDs - the holy grail we talked about way back in college. And similar technology lets you build 100 foot video screens anywhere you want.

    That old flourescent fixture I built way back when kept moving with me - from my parent's house in New York to a rental house on Long Island, to a house in San Diego, through two apartments, another rental house, the first house I owned and now to my current house, where it hangs over the workbench in the garage. And it finally failed for good after over 30 years of service, with both ends blackened and the filaments so gone that not even the Advance ballast could start them any more. And the bulbs were replaced by LED tubes that are even more efficient and look just as good - so at least the ballast will live on.
     
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  3. exchemist Valued Senior Member

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    I know little about LEDs. What's an organic LED? I have to assume it's something to do with organic dyes, where one can get different colours by means of different substituents on the chromophore. But how does that work with a semiconductor? Can you get solid dyes that are also semiconductors or is there some clever combination of a dye with a semiconductor?
     
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  5. exchemist Valued Senior Member

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    P.S. I suppose I could look this up for myself, but it would take some time, so I'm hoping you can summarise it for me, at least enough to narrow down what I need to look up.
     
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  7. billvon Valued Senior Member

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    Normal LED's are semiconductors, and produce light by converting the energy of an electron that can overcome the potential barrier into photons via collisions with dopants in the intrisnic material.

    Organic LEDs use a transparent but conductive anode and an organic* cathode. I don't understand the process there as well yet. They are technically semiconductors but do not follow traditional semiconductor physics.

    (* - organic meaning carbon based of course)
     
  8. Seattle Valued Senior Member

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    My experience with illumination is twofold. I learned a bit about modern leds and the output and size of the emitter and how far it can "throw" that beam if focused with an aspheric lens. If focused to the point where the beam looks like the shape of the emitter (looks like a small house) then it becomes something between a flood light and a laser pointer.

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    You can go camping with a headlamp for general illumination and then you can pull out a compact (modified) "thrower" flashlight that will illuminate a small area several football fields away.

    I've experimented with a light meter measuring lux and using the inverse square law to fine tune which flashlights can be made into "throwers".

    My other experience is with lights and scuba diving. Lights are needed in the daytime or nighttime where I dive (PNW). The best light that I had found was sold as a Light Cannon. It was a halogen light with a tighter beam and a battery that was as heavy as a brick and about the size of a brick.

    Underwater it was neutrally buoyant but it was still bulky. It cost about $300 and a replacement bulb (long lasting) was $100 and replacing the rechargeable battery pack (eventually) was about $150.

    I found a light for $100 made in China with a 30 day shipping time. That's more money than I would generally waste on something unknown from China (at the time) but I found a few independent diver reviews and bought it.

    It takes three 18625 lithium-ion rechargeable batteries (a little longer and bigger around than AA). It is a led flashlight that is almost as focused and bright as the halogen (that was rare at the time, very rare). It uses a Hall Effect sensor for switching so there is a magnetic ring on the outside of the housing for on, high, medium and low. There is no direct connection between the outside of the housing to the inside so no leaking.

    You can't do anything with a halogen light other than turn it on, wait for the ballast to work and then use it on high. It gets very hot and it's not good to turn it off and right back on. With led's none of those things are an issue.

    You can get 2 full dives out of the light and if you need to get in a 3rd dive you can just reduce power. You can also reduce power to look at small marine life that would hide with a halogen beam.

    You can still use this light for signaling (the beam is tight enough). So, this light costs the same as just the halogen bulb and it's much more functional.

    You can make a system to hold the light on to the back of your hand so that you have your fingers free and you just move your hand in the direction that you want to see.

    I also just recently replaced my front porch light (that had replaceable bulbs) with a new unit where the light isn't even replaceable but it's led and is rated to last "forever".

    Even the headlamps in my car are now leds. There isn't even a separate high and low beam. It's always on "high" and when you chose low beam, a mechanical shutter comes part-way down.

    You can also now chose leds either for your house or for flashlights by color temperature so if you want a warm incandescent like beam, you can get that. If you want a pure white beam, you can get that.
     
    Last edited: Jun 15, 2023
  9. exchemist Valued Senior Member

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    Are the anode and cathode the 2 differently doped materials that lead to a narrow band gap? Classically I assume these would be semiconductors like silicon or germanium. I'm having some trouble imagining how one puts together 2 organic materials such that electrons can migrate from one to the other. Normally the electrons are in bonding orbitals and it takes considerable excitation to get them into the first antibonding orbital. I'm clearly missing something fundamental about how these diodes work.
     
  10. billvon Valued Senior Member

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    No, they are two different materials.
    Yep. Like I said, I have a superficial understanding of how LED's are made (and how they work) but I don't understand OLEDs at all. You probably have a better background when it comes to understanding them than I do.
     
  11. exchemist Valued Senior Member

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    OK so I'm on my own. Well, so far I've gathered it's all to do with "excitons". Now I need to get my head round what those really are. The descriptions talk about "holes" as if they are entities, but to me they are a gap where an electron should be, so I'll need to work out how to interpret that before I can get any further in my understanding. Also, at present I do not see how a solid array of organic molecules can have a conduction band into which electrons can be promoted. I'll need to do some more reading.
     
  12. billvon Valued Senior Member

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    That I get. It's just an abstraction, but a very useful one for charge carrier transport in a semiconductor.
     
  13. Seattle Valued Senior Member

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  14. exchemist Valued Senior Member

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    Aha, that's it: LUMO overlap. I had the feeling π* antibonding orbitals must come into it somehow, by analogy with fluorescence. The point must be that in a solid composed of the type of conjugated structure that one needs for a chromophore, there is overlap of LUMOs between adjacent molecules good enough to form a continuum of some kind. I had not thought this would be possible, as the molecules are only weakly bound together in organic solids, by van der Waal's forces. But I suppose the π* states will be more diffuse than the bonding orbitals and can thus overlap more. How very interesting.

    The "holes" then, will be where, in some molecules, an electron has been excited to this LUMO continuum, most likely from the conjugated π system, leaving behind a cationic, electron-deficient molecule. The excitation must be provided by the potential difference across the electrodes.

    Thanks for this. It all starts to make sense.
     
  15. exchemist Valued Senior Member

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    Yes, but as a chemist I want to see what that abstraction means physically, in terms of electrons, molecules, crystal lattices, bonding etc. I think I now have that picture, thanks to Seattle's contribution above.
     
  16. Pinball1970 Valued Senior Member

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    This is kind of up my street - not the electronics materials side, more the resultant colour physics. I will read the posts on the electronics side and see if I can contribute anything useful
     
  17. exchemist Valued Senior Member

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    Look forward to it. We need more proper science on this site.
     
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  18. C C Consular Corps - "the backbone of diplomacy" Valued Senior Member

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    --- Deleted: either clicked the wrong thread or had some brief journey into the TZ. ---
     
    Last edited: Sep 6, 2023
  19. Pinball1970 Valued Senior Member

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    Lighting, like many other things, has had initiatives to reduce emissions/energy use.
    Higher efficiency, less energy better for the environment. All good.
    The down side with LEDs is the type of the light they produce and the definitions of illuminant in a technical setting.
    Specifically things like light boxes and spectrophotometer software.

    From the C.I.E. literature steps have been made to define LEDs recently but this has not filtered down to the software.
    I have one LED illuminant in my software but that is a best fit.
    This is in contrast to established illuminants like D65 a natural daylight analogue, where the software and light sources/ hard ware marry up nicely.
    I am sure all the kit and software will catch up until then we have to use work around.
    Regarding the lights themselves, the SPD has a typical shape, virtually no UV with a spike at 400nm with a huge drop off then rise but loosing red.
    This can impact on how coloured surfaces look under this light source.
    This is called "colour rendering." I have a few measurements and scales I will upload when I am in the office. Illustrate what I mean.
    In short, they are energy efficient, last longer, good intensity, lots of photons, different CCT available (colours) BUT you can get weird effects!
     

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