Strange problem with low energy light bulb

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

When an LED or an LED cluster has to dissipate 20 watts of heat, it
will
probably have to be bigger than a CFL of same power input.

Ok, but try thermally coupling a CFL, or any part of one, to a heatsink.
LED's and their drivers are much more easily adapted to use existing
structures to carry the heat away. That's why they can occuppy smaller
volumes. This is actually done, I mentioned the Clifton Suspension Bridge
in another post, that's covered from end to end in them, they're tiny, and
extremely bright, and they use a small metal cowling to carry heat from the
emitters. They're not 20 watts, more like 10, but the total size of the
lamp is similar to a low-volt halogen, far smaller than an 11 watt CFL.

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

Phosphors have a loss. I expect the ultimate in LED efficiency in the
future will have at least some of the light being the radiation produced
by the LED chips, rather than by phosphors.

I think so too. And I hope so. Phosphors don't allow colour mixing, and
that's one of the biggest strengths of LED's.

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

There are some high power IR laser diodes more efficienct than LPS.
Other than those, laser diodes are less efficient than most sodium lamps.

Ok. I thought more laser diodes were but never mind.. Aren't most class 3B
visible red diodes around 20% efficient or more though? That still leaves a
lot of headroom. Tungsten is often said to be 1% to 2% efficient at making
visible light. So a 100W incandescent 17 l/W at 1% to 2% places the Cree
XR-E's 50+ l/W at 3 times that, up to 6%. These are loose figures but they
suggest that if LED's reach efficiencies like DVD writer diodes, maybe 3 to
4 times the current efficiency can be had. (Not including phosphor losses,
but including LED driver losses). These figures are assuming Imax, 1A per
emitter, if LED's become cheap enough to double the emitter count and drive
each at 500 mA, the efficiency will go up by 50% or more.

 

[Eeyore]

Actually, it's more like that of somewhere between a "cool white" and a
"daylight" old-fashioned fluorescent, with similar color distortions.
There are now some warmer white and higher color rendering index white
LEDs.

I've yet to see a spectrum published for those 'white' leds. I assume it must be
similar to CFLs.

Graham

 

[Eeyore]

They are now getting color temperature as low as mid 4,000's with no
compromise in light output.

4500K is still somewhat blue for most peoples' taste.

Graham

 

[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 ?

In my experimental 45 watt, 9- 5 watt Luxeon array, I use copper, aluminum, and a fan.
DC drive is nice.

The normal home doesn't have DC. What do you use for current limiting
and how much power does that dissipate ?

Electronic ballasts for fluorescent lamps (including the ones in all
spiral and most other screw base CFLs) require DC, so require conversion
of AC to DC, and for that matter back to AC of a higher frequency. Many
of those don't have huge losses, in fact usually less loss than iron core
inductive ballasts.

I was asking about LED drivers not CFLs.

CFLs already include those losses in their stated power. LED fans only ever quote the DC
input power required for the 'chip'.

Talk about an uneven playing field !

Graham

 

[Eeyore]

[email protected] (Don Klipstein) wrote


Ok. I thought more laser diodes were but never mind.. Aren't most class 3B
visible red diodes around 20% efficient or more though? That still leaves a
lot of headroom. Tungsten is often said to be 1% to 2% efficient at making
visible light.

Wikipedia says 2.6% for the ubiquitous 100W tungsten filament bulb and 3.5% for
quartz halogen.
http://en.wikipedia.org/wiki/Luminous_efficacy


Graham

 

[Jasen Betts]

In any case don't 'white leds' use the same phosphor method of producing light
that CFLs do ?

some have yellow fluorescent dye and a blue LED die, it's sort of the
same, but I think the fluorescent lamp has a better spectrum.

Bye.
Jasen

 

[Mr.T]

4500K is still somewhat blue for most peoples' taste.

You must really hate daylight then!

MrT.

 

[Dave Plowman (News)]

You must really hate daylight then!

Most domestic lighting is used after dark and the colour temperature last
thing in the day is nothing like 4500k.

 

[Albert Manfredi]

You must really hate daylight then!

Daylight for artificial lighting is rather annoying. Maybe humans have
been conditioned to want warmer lighting at night, after 10s of
thousands of years of getting by with fire as light source at night.

I find the 3000K of my CFLs to be barely warm enough.

Bert

 

[Lostgallifreyan]

Wikipedia says 2.6% for the ubiquitous 100W tungsten filament bulb

For a 110V type at 1700 lumens, perhaps. 240V types only put 1200 lumens.

 

[Lostgallifreyan]

I've yet to see a spectrum published for those 'white' leds. I assume
it must be similar to CFLs.

?
That Cree document I cited has extensive detail. Several graphs for various
types. Also, they do a 'binning and labelling' document that shows plots of
all types on a cromaticity diagram. I had to think a bit to work out where
my LED torch was on that, but it's all there.

 

[Lostgallifreyan]

Most domestic lighting is used after dark and the colour temperature last
thing in the day is nothing like 4500k.

No. It's akmost certainly much hotter. While it's at its lowest brightness,
the light of a clear day fading is biased extremely toward blue. The rods
in the eye make use of that, it's why greens and blues look brighter than
red flower petals at twilight.

 

[Lostgallifreyan]

CFLs already include those losses in their stated power. LED fans only
ever quote the DC input power required for the 'chip'.

Talk about an uneven playing field !

Not their fault, exactly. CFL's rarely come without a supply attached now.
Also, LED of this kind are new, very few complete lamps with supplies exist
yet, compared to CFL's. Also, LED's run on a very different range of
supplies. Try running any fluorescent tube off a battery and a resistor.
LED's have a modularity that makes it sensible to specify them directly.

If you want to know the total power, it's not the LED maker's job to
specify any PSU they're not making themselves. You need to look at what
PSU's are available. It's only two specs for power conversion efficiency to
consider. Small inconvenience compared to what's gained.

 

[GregS]

Daylight for artificial lighting is rather annoying. Maybe humans have
been conditioned to want warmer lighting at night, after 10s of
thousands of years of getting by with fire as light source at night.

Not only that, but pinpoint sources of light have glare. Daylight is dispersed.

greg

 

[Lostgallifreyan]

[email protected] (GregS) wrote in

Not only that, but pinpoint sources of light have glare. Daylight is
dispersed.

Which is why LED's work so well when projecting on a white surface. I've
found an LED torch with an XR-E in it to be the best portable light source
I've ever had, If pointed at a ceiling it works better than a small
fluorescent. By 'better' I mean more usable for working with. I'd need a
lot more power to get that with longer wavelengths.

 

[msg]

Daylight for artificial lighting is rather annoying.

<snip>

For some of us in cold climates with little daylight during the winter
season, seasonal affective disorder can be a serious problem; bright
daylight wavelength lighting at night and in the morning is necessary
as a therapy.

BTW, why is this thread crossposted to so many newsgroups? I suggest
removing r.a.t., s.e.b. and s.e.t.a. at least for followups.

Regards,

Michael

 

[Arny Krueger]

In USA, plenty of 40 watt incandescents are rated to produce 445 to 500
lumens. My experience is mostly CFLs consuming 25-30% of the electricity
of "standard" incandescents of same light output.


Everyone else who wants to relamp with CFL, watch out with recessed
ceiling fixtures.

Why? The above successful conversion was in recessed ceiling fixtures.

Strangely nough, CFLs are actually more efficient at
producing heat conducted to the immediately surrounding air than
incandescents are, by producing a lot less infrared. I tried this - a 42
watt CFL heats up a fixture slightly more than a 60 watt incandeswcent
does, at least when I tried it. Make sure your fixture does not get too
hot for the CFL. Not only can excessive heat shorten their lives, but
also excessive heat can make them run dim as well as excessive cold can.

Our sucessful implmentation in recessed ceiling fixtures did not do anything
like matching the wattages. I think that the ratio was from a 150 watt
incadescent to two 32 watt CFLs.

 

[Don Klipstein]

[email protected] (Don Klipstein) wrote in


Ok. I thought more laser diodes were but never mind.. Aren't most class 3B
visible red diodes around 20% efficient or more though? That still leaves a
lot of headroom. Tungsten is often said to be 1% to 2% efficient at making
visible light. So a 100W incandescent 17 l/W at 1% to 2%

More like 6-7%. Each watt of tungsten radiation in the 400-700 nm range
is around 250 lumens.

places the Cree XR-E's 50+ l/W at 3 times that, up to 6%.

Figure around 250-300 lumens per watt of "white LED light". Looks like
those achieve about 20%.

683 lumens in a watt of light only applies for a wavelength around 555
nanometers, where the human eye's photopic sensitivity is highest. For
other wavelengths, multiply 683 by the "photopic function".

These are loose figures but they
suggest that if LED's reach efficiencies like DVD writer diodes, maybe 3 to
4 times the current efficiency can be had. (Not including phosphor losses,
but including LED driver losses). These figures are assuming Imax, 1A per
emitter, if LED's become cheap enough to double the emitter count and drive
each at 500 mA, the efficiency will go up by 50% or more.

- Don Klipstein ([email protected])