The next more important thing, which people don't realize, but it's both
important from a cost as well as from an efficiency perspective, is the package.
So once you have this LED dye, you have that, typically,
that package looking something like this, with a dome on the top.
And the new packet, and if you're ever using a bulb you have this this
package on the top, which has phosphorus coating.
And then you also have this luminaire, which
is a housing for many of these bulbs together.
And a lot of the cost as well as the.
manufacturing cost.
So if you see the substrate, the sapphire
substrate as such does not add too much cost.
The epitaxi of galium nitrite does add around 20% of the cost.
Then, a lot of the cost actually comes from this packaging.
And, we talked about packaging with respect to chips,
but it's also, again, very important with respect to
LEDs.
[COUGH]
So, this package achieves
two dual purpose. It helps in extracting the light.
The way it does is that you have a lot
of these surfaces that you can direct your incoming light out.
And also it acts as a heat removal it plays a very
important role, role of improve, of taking that heat out of that system.
And
Taking the heat out of the system is actually very important.
Because if you have a temperature change in your LED that
can change your output as well as your color of your LED substantially.
So this is blue LED operating as minus 20 C, but if
it rises in temperature by 115 degrees, it completely changes your LED.
So your color of your LED might change
completely if you don't pay attention to the packaging.
And with your efficiency decreases if your temperature
rises, and your color goes if your temperature rises.
So this packaging and getting that heat out is very important.
And LEDs especially, if you operate them in a cool environment.
I mean if you put
them in a fridge, they are much more efficient if
you are able to keep your temperature to a minimum.
The last thing which is related to how do we actually operate these LED lamps or,
you know, how do we, what control circuit do we use for operating them?
And that is actually a very important topic, as well, because these, these are
one of the few devices which uses a diode in a forward bias mode.
And, controlling our diode, especially in a forward bias mode, is very, is a very
difficult thing to do because your colorant is, is exponentially
depending on your voltage, so even if your voltage drifts
a little bit If you're a distance, if you're anywhere
between this and you're applying a constant voltage so to start.
There's a little bit, the coloring can actually change quite a lot.
So,
both the temperature and the voltage is important.
So you could have two schemes to drive your LED.
You could apply a constant voltage, so you
know you can have a constant voltage scheme.
Or you can have a constant balance current scheme.
This is very dangerous for LED lamps. So, what is more commonly used is you
drive it with a constant current source. It does add a, a little
bit of cost. Because you have to buy a.
If you're a E background you have these back boost converters, so you have to
buy a buck converter which converts a
constant voltage source into a constant current source.
And there are multiple companies which sell this nationally, one of them.
But you have to decide if you want to
have a stable operation of your LED for your bulb.
[COUGH]
So another thing which is important with respect to lighting especially if
you are using it in the house is the ability to dim it.
So you could actually have two scemes to dim it.
One is you could change the voltage.
That's how you typically, most of your dimmers in your house work.
And that's analog dimming.
Or you could have this pulse fade modulation
where you power your LED with these different
pulses and you change the duty cycle of these pulses to give you different output.
So, the question is which, which do you think
would be better for dimming the lighting scheme where you.
where you just change the voltage or where you use a pulse rate modulation.
So, in, in, in actual life what
is preferable is PWM based dimming, though actually
analog can also be used and is in fact used many a times.
But but again, what you achieve with analog is that your since it's so
dependent on voltage, your wavelength can change, your color temperature can change.
But with digital living, you have that constant current level.
And you get, if you switch it on and
off very fast, your eye doesn't receive it, right?
also, these devices don't have any LEDs, also don't have any durability problems.
You can cycle them as many times.
They're much more stable than, you know, a Flash memory cell,
where using that kind of a scheme might get you in trouble.
But, for LEDs, actually, PWM is preferred for LED based lighting,
and especially if you're using that Buck converter that also
allows you to achieve this achieve this dimming using the pulser.
[COUGH]
So, actually, I we probably will stop early
today, but let's, you know, summarize our learning.
So, in terms of lifetime, which one do you think has better.
How much is, that picture had
one CFL equal to ten incandescent. So how much of the lifetime for each?
. Yeah, so incandescent is about 1000.
CFL is around 10,000.
LEDs is , people can say anything. But it doesn't go bad
.
What happens is your output degrades over time.
It usually doesn't fuse out or anything.
The people say it's above 30K.
That's when your output becomes 70 percent of the.
Dimmable, LED, and incandescents are dimmable,
but the schema used are different. Incandescents typically use analog.
They change the voltage.
That's how most dimmers in your house work.
LEDs,
speed up
. Instant on the CFL is not typically
instant on. it also has a mercury
problem, so, it's, you should not throw CFL in your trash, and stuff.
in terms of cost we talked about, you know, the LED are typically three to
four times more expensive than CFL, and
incandecence are very cheap. So.
.