Re: Strange problem with low energy light bulb

[Eeyore]

Eeyore wrote:
Arfa Daily wrote:

With a bit of work, I'm sure that they [LEDs] will
also get to the point where they can replace a standard filament bulb, in
the same sized package, unlike a CFL which has to accommodate the ballast.

To run LEDs efficiently from 240V AC will also require some active electronics.
I see no-one ever factors in the power losses that'll be associated with that.

When you use up the watts, you get heat. The lamp has to efficiently get
rid of it. May even need a fan.

Quite possibly so. How many watts does the fan need ?

I have one here that's 40mm sq. It still uses 1W.

I'm actually using a CPU sink/fan combo, but the LED's are epoxied to a copper
plate. I even have diamond dust as a buffer/insulator. To close space the LED's
I needed the best thermal transfer. Did I forget to mention the Peltier device.
I am also using unmounted LED's.



Nothing is compact. I use a large variable supply.

And the efficiency of that is ?

There is 45 watts going to the LED's.
About 20 [email protected] amps. 3 series sets of LED's. You cannot look at the light.
The device was intended to be flashed in the final form. peaking at about 60 watts.

So how do you control the LED current ? I imagine you may have current sharing issues with parallel chains
too.

What's the AC input watts ?


Graham

 

[Lostgallifreyan]

But that's not mains. Nor do LEDs run off a voltage source. You need
to control the current.

Of course it's not mains, I just cited the one example I had, I mentioned
mains later. Might be better to read the whole post before answering, it
wasn't a big one.

As for current not voltage, that is why I said POWER conversion. That's
what LED drivers do, they put out a controlled CURRENT. It is correct to
call this power conversion.

I very much doubt it. One very important point however is that these
need to be driven with a constant *current* not a constant voltage and
that's typically a lossier method too.

Well, I found one and posted about it already in a later post. 82%, Not too
shabby. That runs directly off 240VAC.

Now, how efficiently can you convert VOLTAGES?? What's the best efficiency
to get say, 240VAC to 30VDC? Take it, whatever it is, then deduct the 5%
from the DC power converter I mentioned above. I suspect it can be better
than 82% total? I imagine >90% might be had. You say that the conversion to
current is the inefficient bit, but that's the task I cited as being done
at 95%. That's why I mentioned the DC power converter, because it is
relevant.

 

[Eeyore]

Eeyore wrote



Table: Flux Characteristics (Tj = 25°C)
Cree XR-E type P4, 80 lumens at 350 mA
Cree XR-E type Q4, 100 lumens at 350 mA
Graph: "Relative Intensity vs. Current Tj = 25°C)"
Line rising through 100% output at 350 mA to >220% at Imax of 1A.
Source: http://www.cree.com/products/pdf/XLamp7090XR-E.pdf

Logical inference is that the P4 can output >176 at 1 amp, and the Q4 can
do >220 lumens at 1 amp.

OK. That's 3.7W of input power. Giving 47.5 and 59.5 lumens/W respecitively for
those 2 leds.

NIST tested an XR-E Xlamp at 350 mA and found outputs exceeding that
claimed in the data sheet. They did not measure the output at 1A but they
did certify the lumens per watt.
Source:
http://www.cree.com/products/pdf/NIST XLamp LED Document.pdf

About 84 lumens @ 350 mA and 75 lumens/W at this lower current.

They did not test the output at 1A, or at least did not certify it, but
either the LED's die before you manage to push 1A through them, or they can
do what is claimed. Even if there is a fall-off with current, the Q4 type
will definitely exceed 176 lumens at 1A.

185 lumens using your figure of 2.2x times the reference brightness @ 1A.

Graham

 

[Lostgallifreyan]

OK. That's 3.7W of input power. Giving 47.5 and 59.5 lumens/W
respecitively for those 2 leds.

Tell that to NIST >

 

[Lostgallifreyan]

185 lumens using your figure of 2.2x times the reference brightness @
1A.

That should satisfy you then. You challenged me to cite proof of 176 mW as
if I was claiming too much. Are you now saying I'm wrong because it's not
EXACTLY 176 mW? If so I'm done discussing the matter.

 

[Eeyore]

Lostgallifreyan wrote

Here's one at 82%: http://www.magtechind.com/__LED_Lighting_PSU/Anz107.pdf
I saw better, but this was one I found while looking for a specific item.
If I find something significantly better on 240 VAC I'll post again.

I doubt you'll do much better actually. 82% sounds about right (not 95%) however
that is at max load.

I see they don't state efficiency for the lower power models.

Graham

 

[Eeyore]

Eeyore wrote


Higher intensity. Might be nonlinear, as in greater efficiency if you pump
them harder. Might be different materials. I don't know for sure though.

Definitely smaller size, so if you're going to be a stickler for full
context such as analysis of lumens per watt of actual mains input, you must
take all of the context. People have alreay said (rightly) that LED lamps
won't have the trouble that CFL's have in fitting most current luminaries.

Well actually I wonder about that. Especially replacements for those 'low
voltage halogen' types like these.
http://www.lightingfx.com/item--Halogen-GU10--51

There's not actually any easy way to lose the heat. The 'enclosure' is very
small.

That's obviously important regarding watse and expense.

More: LED's are growing more efficient all the time. It might be that in
future these lamps might be directly driven by encapsulated laser diodes
emitting near UV to pump phosphors. Laser diodes have efficiencies beyond
low pressure sodium, they leave it in the dust. It's likely that this
technology will quickly make CFL's look barbarous.

I'm not so sure about the quickly bit.

Graham

 

[Lostgallifreyan]

Well actually I wonder about that. Especially replacements for those
'low voltage halogen' types like these.
http://www.lightingfx.com/item--Halogen-GU10--51

There's not actually any easy way to lose the heat. The 'enclosure' is
very small.

No fair! > You try fitting a CFL in there. That's why you're pulling
teeth out of the biting argument in favour of LED's isn't it? Most of the
time in this thread you're advocating CFL's, so this is a spurious issue.

Actually, the Cliften Suspension Bridge in Bristol has its chains entirely
lit by exactly the type of LED-based lamp that replaces little tunsten
halogens. There are three emitters per lamp. The lowest is too high to get
a good look at, but they appear to be Cree or Luxeons in small parabolic
reflectors. Sure, a bridge doesn't have many cooling problems most times,
but those 'chains' are mighty plates of iron, and on summer nights they are
hot. Doesn't stop those lamps working though.

 

[Lostgallifreyan]

Cliften Suspension Bridge

That is so embarrasing I have to correct it. 'Clifton'.

 

[Eeyore]

Even at >120°C the chips put out 70% of 25°C rated output, and I doubt even
ten closely packed emitters will get that hot if convection can keep the
mounts below 85°C. Ten emitters in a lightbulb's space couldn't even get
that hot unless they had less than twice the efficiency of 100W tungsten
lamps.

How do you work that out ?

Ten emitters of the current best type account for about 34W ! You'll have a
hell of a job keeping them below 70C or so in the space of a current lighbulb !
Forced cooling would be essential and that's going to be annoying. How many fans
last 50,000 hrs too ? I'm sure they'd get end up overheating through dust
build-up reducing fan efficiency too.

Graham

 

[Lostgallifreyan]

How do you work that out ?

Ten emitters of the current best type account for about 34W ! You'll
have a hell of a job keeping them below 70C or so in the space of a
current lighbulb ! Forced cooling would be essential and that's going
to be annoying. How many fans last 50,000 hrs too ? I'm sure they'd
get end up overheating through dust build-up reducing fan efficiency
too.

Ok, I think it will run hotter than I was suggesting, but you're forgetting
something too, a much greater chunk of that imput wattage will be emitted
as light, not heat, compared with tungsten lamps.

 

[Eeyore]

Eeyore wrote


Of course it's not mains, I just cited the one example I had, I mentioned
mains later. Might be better to read the whole post before answering, it
wasn't a big one.

As for current not voltage, that is why I said POWER conversion. That's
what LED drivers do, they put out a controlled CURRENT. It is correct to
call this power conversion.

However you did mention volts previously. It wasn't me who did that.

Well, I found one and posted about it already in a later post. 82%, Not too
shabby. That runs directly off 240VAC.

Now, how efficiently can you convert VOLTAGES?? What's the best efficiency
to get say, 240VAC to 30VDC? Take it, whatever it is, then deduct the 5%
from the DC power converter I mentioned above. I suspect it can be better
than 82% total? I imagine >90% might be had. You say that the conversion to
current is the inefficient bit, but that's the task I cited as being done
at 95%. That's why I mentioned the DC power converter, because it is
relevant.

LEDS operate at lowish voltages. You tend to get lower efficiencies with at
lowish voltages, largely due to rectifier losses.

I doubt you'll much better 85% power conversion efficiency overall from the AC
line to the LED package actually. That would be a *very* good figure.

Graham

 

[Eeyore]

Eeyore wrote


That should satisfy you then. You challenged me to cite proof of 176 mW as
if I was claiming too much. Are you now saying I'm wrong because it's not
EXACTLY 176 mW? If so I'm done discussing the matter.

No, it's fine. I hadn't previously noticed anything above about 150 lumens.

Graham

 

[Lostgallifreyan]

[snip]

However you did mention volts previously. It wasn't me who did that.

I see now, that's just loose phrasing by me that led you to misinterpret.

We both know that LED's are current driven. What I meant was that the input
can range between 5 and 32 volts. The conversion is to one of a variety of
preset fixed currents.

 

[Lostgallifreyan]

LEDS operate at lowish voltages. You tend to get lower efficiencies
with at lowish voltages, largely due to rectifier losses.

I doubt you'll much better 85% power conversion efficiency overall
from the AC line to the LED package actually. That would be a *very*
good figure.

LED drivers chain LED's to limit that problem. The one I bought can chain 7
LED's.

 

[Eeyore]

Eeyore wrote



No fair! > You try fitting a CFL in there. That's why you're pulling
teeth out of the biting argument in favour of LED's isn't it? Most of the
time in this thread you're advocating CFL's, so this is a spurious issue.

To be honest, I'm not actually advocating any specific technology. I am however
very interested on Philips new compact 'CHLi' halogens.
http://www.lighting.philips.com/gl_...main=global&parent=4390&id=gl_en_news&lang=en

I have seen LED 'replacements' for that GU10 type touted, but it's clear they
must have very much lower light output.

Graham

 

[Lostgallifreyan]

No, it's fine. I hadn't previously noticed anything above about 150
lumens.

It changes fast. I lost interest in LED's around the time of the 14
candela amber Toshiba 10mm types, because laser diodes were more fun.
Things have changed big time. I really do think they'll overtake CFL's so
fast that most of the public, especially legislators, will have no time to
adapt except in sudden jumps. They'll be thankful to do it too, once they
face the clamour of public dissent at having to throw away good light
fittings to suit the intended ban of tungsten lamps.

While something could stall the development of LED's there seems to be no
sign of that, if anything it will likely accelerate as technology further
blurs the distinction between LED and laser diode.

 

[Eeyore]

Eeyore wrote in

Ok, I think it will run hotter than I was suggesting, but you're forgetting
something too, a much greater chunk of that imput wattage will be emitted
as light, not heat, compared with tungsten lamps.

Only about 10%. There'll still be 34W to get rid of. And I forgot the
dissipation from the electronics too ! That'll be another ~ 5W so we're back to
where we were.

Graham

 

[Eeyore]

Eeyore wrote


LED drivers chain LED's to limit that problem. The one I bought can chain 7
LED's.

Even then, the seondary rectifiers alone will consume about 5% of the power.

Graham

 

[Lostgallifreyan]

To be honest, I'm not actually advocating any specific technology. I
am however very interested on Philips new compact 'CHLi' halogens.
http://www.lighting.philips.com/gl_en/news/press/product_innovations/pr
ess_2006/ecoboost_technology.php?main=global&parent=4390&id=gl_en_news&
lang=en

I'm keen on the developments in halogen lamps too. They have a light
quality I consider second to none. I hope broadband phosphor mixes will be
improved, but they still don't work like a small efficient halogen does.

I need to stop now, want to watch Minder. I need a rest.