Hey guys, I’m curious. Please correct anything false here as I am presenting my understanding and hoping for correction so I am properly tuned in thinking.  Growing up I knew LED as indicators of low intensity and limited colors. I knew them as direct emitters where the chip directly emitted red or green or yellow light. Then came blue and white while I was working at radio shack in early 2000s. Both of those were clear and direct emitters and I under the understanding that a white to be a red, green, and blue chip all shining  together. That’s where my understanding stopped regarding LED. Then when LED’s started being used in flashlights, I noticed the yellow chip or lump. I learned that this is a blue, not UV LED that serves the same purpose as mercury vapor, to simply excite the yellow phosphor which then is tuned chemically to emit the desired color temperature. I am almost thinking early LED household replacements (Philips L Prize) were trying to use direct emitters with three color chips like the baby whites of the early 2000’s leading to huge heat sinks and $50 bulbs lol. I may be wrong. So I never liked the chip in plastic bulb style at all. But I’m loving the all glass filament LED for sure. I do understand how they work instead of one large blue chip under a yellow phosphor lump, they ha e loads of baby chips  in a row that are covered with a tube of phosphor like insulation on a wire.

A question, why didn’t they coat a glass bulb with phosphor and use blue chips to excite the powder like a fluorescent? I’m thinking poor efficiency and odd light patterns.

Finally my main question, is that how all glass T8 LED works? I found one at work, a Sylvania Substitube in a bathroom and removed it to examine. It looks like it’s glass coated with normal phosphors and there’s a metallic strip along the back I believe holds a strip of the blue filament LED’s shining in. Or....are those white chips (blue with yellow lump) and the white on the tube is not phosphor but rather just a light dissipator sort of like a soft white incandescent.

 Thanks a million guys!!!

Mike

Because the tecnology of directly getting white light without using phosphores from the chips has not being reached yet, we use blue LEDs with the phosphores like in old fluorescent tubes because it's way cheaper.

They don't mix red green and blue chips together because it will have a horrible CRI, even worse than the cheapest LED bulb you can get.

The "phosphore coating" of the LED fluorescent retrofits is just a difusser dust like in coated incandescent lights.

LED strip inside a glass tube?

LED strip inside a glass tube?

Yep, that's the way how all LED tubes works.

Yep, that's the way how all LED tubes works.

Well, it is a row of LED chips, that is all it has common with the selfadhesive strips.


And for the direct light generation: That is physically impossible without high resistive losses in the chip structure.
The way the LED physics work, the photon energy as well as the junction voltage drop follow the band gap energy of the junction. So a 3eV blue LED has no other way than having 3V voltage drop when excluding the resistive drops on parts just carrying current to the main junction.
White light needs to be "assembled" from multiple spectral lines.
So a white emitter would have to consist of areas with varying band gap across the chip (that is perfectly possible to make).
But problem is, you will end up with essentially diodes with varying forward voltage all in parallel. And that means the current will flow only through the area with the lowest voltage drop (so the red section) and the rest will be dark.
So to make the current flow through all sections, you need to include a kind of ballasting resistances into the structure, to add the extra voltage to the lower voltage (red, yellow) sections in order to get the overall voltage sufficient to light the higher voltage (blue,...) sections. In order to maintain control over the color balance, there would have to be extra resistance with all of the sections. Plus the overall color will be heavilly current dependent (at lower currents the voltage drop across the resistors will get reduced, reducing most the current through the higher voltage, so blue, sections first before anything noticeable happens to the red), plus as typical with semiconductors, everything is strongly temperature dependent, so the optimal current for a good balance would have to exactly follow the LED chip temperature.
In total you loose majority of the input power in these ballasting resistance structures, so the overall efficiency becomes very low.

In fact LEDs using this concept were made, but because of all the drawbacks became obsolete even sooner than they ever ramp up.


Using monochromatic LED allows nearly no resistances, so no additional losses in the LED structure, plus being monochromatic it can in no way cause any color imbalance (when the rest is derived from its output).

Thank you very much guys.  Oh man, what a disappointment about the T8 LED, I feared just a diffuser powder like soft white incandescent. Think I’m gonna stay incandescent/fluorescent/HPS/LPS/MV.

Early on, a few manufacturers experimented with remote phosphor tech, notably this philips lamp



I also found this clip:

https://www.youtube.com/watch?v=lHD657EGoCY

They never really caught on. I believe the main reason is each lamp potentially requires custom phosphor moldings. From a tooling and lead-time perspective, this gets expensive when light bulb design changes every few months. Also, they tend to be starkly yellow when off, which may be off-putting to consumers.

I see!! Now that makes sense, yes people would not like the yellow phosphor I didn’t think of that. Besides less efficiency. That’s so cool that someone made it like this though, imagine a yellow fluorescent tube. I wonder why the phosphors are yellow and not white like the UV absorbing in the fluorescent. Blue absorbing must just be yellow naturally.