LED lights for filmmaking

[Daniel Kelly (AKA Jack)]

Hello,

I recently saw an advert for some LED lights for filmmaking. They looked
perfect - very efficient, flicker-free, dimable from 0-100% etc. The
problem is that they're extortionately priced. So now I want to make my own
LED lights for use on film...

Has anyone tried this? What should I be careful of? Can I vary the colour
temperature of the lights by pushing more or less current through the LEDs?

Even better - does anyone know of any LED lights suitable for film that I
could buy off the shelf here in the UK?

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp (ultimately I'd like to
build in a remote control so I can change dim the light whilst I'm looking
through the viewfinder on my camera)
- cheap!
- highly efficient
- stable and predictable colour temperature (it would be very cool if I
could change the colour temp with a switch... my research into LEDs so far
has hinted at the possibility of changing the colour temperature by
increased in the current).

Please do let me know your thoughts - any leads you can give me will be very
well received

Thanks,
Jack

 

[Richard Crowley]

"Daniel Kelly (AKA Jack)" wrote ...

I recently saw an advert for some LED lights for filmmaking.
They looked perfect - very efficient, flicker-free, dimable
from 0-100% etc. The problem is that they're extortionately
priced.

Have you priced white and/or blue LEDs? I'm all for rolling
my own equipment (working on a couple of ideas for compact
flourescent), but the price and efficiency of white and blue LEDs
isn't there yet, IMHO.

So now I want to make my own LED lights for use on film...

Has anyone tried this? What should I be careful of?

You haven't mentioned what KIND of lights you are talking about.
A small "fill" light that fits in the accessory shoe on top of your
camcorder is one thing. A 500W or 1000W equivalent elipsoid
or fresnel is something else again. And a big soft-light is yet
annother thing. IMHO, only a small, camera-mounted fill light
might be practical at this time (if you have deep pockets).

Can I vary the colour temperature of the lights by pushing more
or less current through the LEDs?

I would doubt it. LEDs don't produce light the same way as
filament-based lamps. Even the range of output is relative
limited. Full-range dimming can be done only by pulsing the
LEDs and adjusting the pulse-width. If you do this at a high
enough frequency, it appears to be "flicker-free".

Even better - does anyone know of any LED lights suitable
for film that I could buy off the shelf here in the UK?

I have seen some theatrical lighting equipment that claims to
have LED sources, but as you say, they are scandalously
expensive.

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp
(ultimately I'd like to build in a remote control so I can
change dim the light whilst I'm looking through the viewfinder
on my camera)

With the price of the LEDs, the cost of the dimming parts of
the circuit (power transistors, heat sinks, etc.) will seem cheap.

- cheap!

Don't hold your breath. At least for a few more years.

- highly efficient

I seem to recall something about big heat-sinks on the backside
of the LED sources, and even fan cooling. Doesn't bode very
well for efficiency if all that power is going into useless heat.

- stable and predictable colour temperature (it would be very
cool if I could change the colour temp with a switch... my research
into LEDs so far has hinted at the possibility of changing the
colour temperature by increased in the current).

Doesn't seem likely. OTOH, people even make full-color image
displays with LEDs by close-spacing red, green, and blue LEDs
and pulse-width modulating them to produce any color you want.
"white LEDs" are sometimes nothing but red, green, and blue
LED chips in the same package. The colors combine to make what
appears to be "white" to us exactly the same as color displays
CRT, LCD, etc.)

Please do let me know your thoughts - any leads you can give
me will be very well received

In the last year or so, there has been a lot of discussion of white
LEDs and the circuits used to drive them from batteries over on
the newsgroup news:alt.binaries.schematics.electronic Dunno
about any of the other newsgroups you have cross-posted this to.

At least this is my perception of the current state of the art. I
would be happy to learn that there is better news.

 

[Martin Underwood]

"Daniel Kelly (AKA Jack)" <d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote in message
news:cl5mu4$g2e$1@uns-a.ucl.ac.uk...

Hello,

I recently saw an advert for some LED lights for filmmaking. They looked
perfect - very efficient, flicker-free, dimable from 0-100% etc. The
problem is that they're extortionately priced. So now I want to make my
own
LED lights for use on film...

Has anyone tried this? What should I be careful of? Can I vary the
colour
temperature of the lights by pushing more or less current through the
LEDs?

Even better - does anyone know of any LED lights suitable for film that I
could buy off the shelf here in the UK?

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp (ultimately I'd like
to
build in a remote control so I can change dim the light whilst I'm looking
through the viewfinder on my camera)
- cheap!
- highly efficient
- stable and predictable colour temperature (it would be very cool if I
could change the colour temp with a switch... my research into LEDs so far
has hinted at the possibility of changing the colour temperature by
increased in the current).

Please do let me know your thoughts - any leads you can give me will be
very
well received

LEDs as film lights? Sounds highly intriguing. I thought that LEDs tended to
produce fairly monochromatic light, whereas you'd want broad-spectrum white
light for filming. Also, I can't imagine LEDs producing sufficient light to
illuminate something more than a few millimetres away!

 

[Bruce Murphy]

"Martin Underwood" <me@privacy.net> writes:

LEDs as film lights? Sounds highly intriguing. I thought that LEDs tended to
produce fairly monochromatic light, whereas you'd want broad-spectrum white
light for filming. Also, I can't imagine LEDs producing sufficient light to
illuminate something more than a few millimetres away!

You're forgotting how frightening the higher-intensity LEDs can be.

A couple of years ago, a story turned up about an LED-based theatre
light that generated relatively little heat and was tuneable in colour
(presumably three lighting components in varying amounts). If it was
tuned well to your sensor it could provide light that looked /white/
but unlesss the individual LEDs were quite broad band, you'd still get
crap colour rendition of things withing the field of lighting.

I really wonder what the current state of the art is for these things.

B>

 

[Ian Stirling]

In sci.engr.lighting "Daniel Kelly \(AKA Jack\)" <d.kellyNOSPAM@nospam.ucl.ac.uk> wrote:

Hello,

I recently saw an advert for some LED lights for filmmaking. They looked
perfect - very efficient, flicker-free, dimable from 0-100% etc. The
problem is that they're extortionately priced. So now I want to make my own
LED lights for use on film...

Has anyone tried this? What should I be careful of? Can I vary the colour
temperature of the lights by pushing more or less current through the LEDs?

Generally no. No.

Even better - does anyone know of any LED lights suitable for film that I
could buy off the shelf here in the UK?

Many.

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp (ultimately I'd like to
build in a remote control so I can change dim the light whilst I'm looking
through the viewfinder on my camera)
Not a problem.

- cheap!

Extreme problem. Expect to pay well over 3 quid a watt, in quantity.

- highly efficient
Nope, about as good as halogen bulbs, maybe a bit more if you go with

mixed colours of LEDs, but then you run into new problems.

- stable and predictable colour temperature (it would be very cool if I
could change the colour temp with a switch... my research into LEDs so far
has hinted at the possibility of changing the colour temperature by
increased in the current).

It alters, but generally not in useful ways.

Please do let me know your thoughts - any leads you can give me will be very
well received

Wait a decade or two.

 

[Phil]

FOLLOW UP settto uk.tech.broadcast, and not 9 groups

In article <m2hdop4hoi.fsf@greybat.rattus.net>, Bruce Murphy
<pack-news@rattus.net> wrote:

"Martin Underwood" <me@privacy.net> writes:

LEDs as film lights? Sounds highly intriguing. I thought that LEDs
tended to produce fairly monochromatic light, whereas you'd want
broad-spectrum white light for filming. Also, I can't imagine LEDs
producing sufficient light to illuminate something more than a few
millimetres away!

You're forgotting how frightening the higher-intensity LEDs can be.

A couple of years ago, a story turned up about an LED-based theatre
light that generated relatively little heat and was tuneable in colour
(presumably three lighting components in varying amounts). If it was
tuned well to your sensor it could provide light that looked /white/ but
unlesss the individual LEDs were quite broad band, you'd still get crap
colour rendition of things withing the field of lighting.

I really wonder what the current state of the art is for these things.

B

Phil: The original poster may be confusing on-Camera LED assemblies
designed for on-axis chromakey (in green or blue or I think white** at IBC
this year) with full-spectrum lighting, which event he white ones don't
supply, sincle they are effectively 'fluoescents' in their light output:
eg starting from an basic excited UV via doped layers or coatings which
emit at selected visible colours (like fluorescent tubes) to give a
'balanced' white - as long as you are not then using that light to analyse
the colour composition of a scene 9as in a camera! ((unless exactly
marching the RGB filter - but even then, it is unlikely to have any
spread, but be 3 or 4 monochromatic sources.))

**used with directional (scoth-light?? or similar name) reflectant
backgrounds, giving good chromakey or matte separation of subject to
background - the efficiency coming also from the directional nature of the
reflective material.
(Which is a couple of hundred for a sqaure metre or 2?)

--
Phil Spiegelhalter: Phil@fillin.co.uk
==== Technical Training for Broadcasters =====
*RE CUE Mobile DV Multi-Camera Production and Non-Linear Editing*

 

[Paul Burridge]

On Wed, 20 Oct 2004 13:53:47 +0100, "Daniel Kelly \(AKA Jack\)"
<d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote:

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp (ultimately I'd like to
build in a remote control so I can change dim the light whilst I'm looking
through the viewfinder on my camera)
- cheap!
- highly efficient
- stable and predictable colour temperature

Colour temperature's one thing; what about the heat problem? You'll be
no doubt bunching these hi-output LEDs together in some sort of
reflective enclosure and they're bound to get very hot when running at
any useful level of brightness. Plus the hotter they get, the more
current they tend to pass (if not limited) which makes them hotter
still and makes for the difficulty in setting a constant level of
brightness. Can they really cope with the intensity of being used
closely bunched together even if you can control the brightness
satisfactorily?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[E. Rosten]

Richard Crowley wrote:

I would doubt it. LEDs don't produce light the same way as
filament-based lamps. Even the range of output is relative
limited. Full-range dimming can be done only by pulsing the

This is not the only way: I have previously built a voltage controlled
current source for driving LEDs, which allows linear, full range
dimming. However, for high powers, this is rather harder to do without
the pulsing approace, due to the heat dissipated by the active devices.

LEDs and adjusting the pulse-width. If you do this at a high
enough frequency, it appears to be "flicker-free".

Which should be quite easy. LEDs can be driven to very high frequencies
easily. I've transmitted a few watts (infra red) at 20KHz (using a
current source driver) with no trouble. I could have gone higher, but I
settled on that frequency.

Even better - does anyone know of any LED lights suitable
for film that I could buy off the shelf here in the UK?


I have seen some theatrical lighting equipment that claims to
have LED sources, but as you say, they are scandalously
expensive.

LEDs are currently rather expensive, at about Ł10 per Watt.

I seem to recall something about big heat-sinks on the backside
of the LED sources, and even fan cooling. Doesn't bode very
well for efficiency if all that power is going into useless heat.

At 90% efficiency, a 1KW source will give off 100W of heat. Consider how
hot a 100W lightbulb becomes. You don't want your LEDs getting that hot.

Doesn't seem likely. OTOH, people even make full-color image
displays with LEDs by close-spacing red, green, and blue LEDs
and pulse-width modulating them to produce any color you want.
"white LEDs" are sometimes nothing but red, green, and blue
LED chips in the same package. The colors combine to make what
appears to be "white" to us exactly the same as color displays
CRT, LCD, etc.)

I believe that some white LEDs operate by giving off blue light anc
converting some to green and red using phosphors. Others work in teh
manner you describe. I would expect that to be more efficient.



-Ed

--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

 

[Daniel Kelly (AKA Jack)]

Brilliant, thanks loads for all your ideas.

There's a fantastic thred over here:

http://www.dvxuser.com/cgi-bin/DVX2/YaBB.pl?board=Links;action=display;num=1071261354;start=0

Thanks,
Jack

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:10ncqt7nc5vir02@corp.supernews.com...

"Daniel Kelly (AKA Jack)" wrote ...
I recently saw an advert for some LED lights for filmmaking.
They looked perfect - very efficient, flicker-free, dimable
from 0-100% etc. The problem is that they're extortionately
priced.

Have you priced white and/or blue LEDs? I'm all for rolling
my own equipment (working on a couple of ideas for compact
flourescent), but the price and efficiency of white and blue LEDs
isn't there yet, IMHO.

So now I want to make my own LED lights for use on film...

Has anyone tried this? What should I be careful of?

You haven't mentioned what KIND of lights you are talking about.
A small "fill" light that fits in the accessory shoe on top of your
camcorder is one thing. A 500W or 1000W equivalent elipsoid
or fresnel is something else again. And a big soft-light is yet
annother thing. IMHO, only a small, camera-mounted fill light
might be practical at this time (if you have deep pockets).

Can I vary the colour temperature of the lights by pushing more
or less current through the LEDs?

I would doubt it. LEDs don't produce light the same way as
filament-based lamps. Even the range of output is relative
limited. Full-range dimming can be done only by pulsing the
LEDs and adjusting the pulse-width. If you do this at a high
enough frequency, it appears to be "flicker-free".

Even better - does anyone know of any LED lights suitable
for film that I could buy off the shelf here in the UK?

I have seen some theatrical lighting equipment that claims to
have LED sources, but as you say, they are scandalously
expensive.

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp
(ultimately I'd like to build in a remote control so I can
change dim the light whilst I'm looking through the viewfinder
on my camera)

With the price of the LEDs, the cost of the dimming parts of
the circuit (power transistors, heat sinks, etc.) will seem cheap.

- cheap!

Don't hold your breath. At least for a few more years.

- highly efficient

I seem to recall something about big heat-sinks on the backside
of the LED sources, and even fan cooling. Doesn't bode very
well for efficiency if all that power is going into useless heat.

- stable and predictable colour temperature (it would be very
cool if I could change the colour temp with a switch... my research
into LEDs so far has hinted at the possibility of changing the
colour temperature by increased in the current).

Doesn't seem likely. OTOH, people even make full-color image
displays with LEDs by close-spacing red, green, and blue LEDs
and pulse-width modulating them to produce any color you want.
"white LEDs" are sometimes nothing but red, green, and blue
LED chips in the same package. The colors combine to make what
appears to be "white" to us exactly the same as color displays
CRT, LCD, etc.)

Please do let me know your thoughts - any leads you can give
me will be very well received

In the last year or so, there has been a lot of discussion of white
LEDs and the circuits used to drive them from batteries over on
the newsgroup news:alt.binaries.schematics.electronic Dunno
about any of the other newsgroups you have cross-posted this to.

At least this is my perception of the current state of the art. I
would be happy to learn that there is better news.

 

[Martin Underwood]

"E. Rosten" <look@my.sig> wrote in message news:41769488.2050303@my.sig...

Richard Crowley wrote:

LEDs and adjusting the pulse-width. If you do this at a high
enough frequency, it appears to be "flicker-free".

Which should be quite easy. LEDs can be driven to very high frequencies
easily. I've transmitted a few watts (infra red) at 20KHz (using a
current source driver) with no trouble. I could have gone higher, but I
settled on that frequency.

Surely if you pulse the LEDs you'll get patterning on the picture due to the
sequential nature of the scanning. For example, if you pulsed the LEDs at
15625 kHz (the line frequency of British TV) you'd get one half the picture
black and the other half white, with the proportion of black to white
varying with the mark:space ratio of the driving signal (ie the brightness
of the light). The only way to avoid this would be to have lots of LEDs all
firing from the same signal but each with a different phase difference.
Maybe the best frequency is one that is a long way from a harmonic of the
line frequency, so that any remaining patterning looks like a random dot
crawl over the picture rather than a static pattern.

Or do LEDs have a fairly long persistence - ie does the light continue for
some time after the driving voltage is removed? If so, the effect of varying
the mark:space ratio would be reduced if the frequency was chosen to be high
enough to avoid significant flicker.

What is the situation with xenon tubes used as TV lights? Are they pulsed
with variable mark:space ratio or are they on continuously with the current
varied to vary the brightness?

 

[Victor Roberts]

On Wed, 20 Oct 2004 17:22:23 +0000 (UTC), "Deep Reset"
<DeepReset@hotmail.com> wrote:

[snip]

I don't imagine the "non-flicker" is possible -about the only way to dim
LEDs is to use PWM - just hope the frequency is very much greater than your
line rate.

As has been stated before, LEDs can be dimmed with a continuous
current. In this case there is no flicker from the LED. The trick is
to make a variable current source with high efficiency. This is done
all the time by using a PWM circuit inside the power converter and
then smoothing (filtering) the current before it is applied to the
load. You get a continuously variable, high efficiency current source
that has very little modulation on its output - and hence no flicker.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

 

[Ian Stirling]

In sci.engr.lighting E. Rosten <look@my.sig> wrote:

Richard Crowley wrote:


I would doubt it. LEDs don't produce light the same way as
filament-based lamps. Even the range of output is relative
limited. Full-range dimming can be done only by pulsing the

This is not the only way: I have previously built a voltage controlled
current source for driving LEDs, which allows linear, full range
dimming. However, for high powers, this is rather harder to do without
the pulsing approace, due to the heat dissipated by the active devices.

A switched-mode current source can use relatively small inductors to
smooth the current to something approximating DC.

 

[Deep Reset]

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:10ncqt7nc5vir02@corp.supernews.com...

"Daniel Kelly (AKA Jack)" wrote ...
I recently saw an advert for some LED lights for filmmaking.
They looked perfect - very efficient, flicker-free, dimable
from 0-100% etc. The problem is that they're extortionately
priced.

Have you priced white and/or blue LEDs? I'm all for rolling
my own equipment (working on a couple of ideas for compact
flourescent), but the price and efficiency of white and blue LEDs
isn't there yet, IMHO.

So now I want to make my own LED lights for use on film...

Has anyone tried this? What should I be careful of?

You haven't mentioned what KIND of lights you are talking about.
A small "fill" light that fits in the accessory shoe on top of your
camcorder is one thing. A 500W or 1000W equivalent elipsoid
or fresnel is something else again. And a big soft-light is yet
annother thing. IMHO, only a small, camera-mounted fill light
might be practical at this time (if you have deep pockets).

Can I vary the colour temperature of the lights by pushing more
or less current through the LEDs?

I would doubt it. LEDs don't produce light the same way as
filament-based lamps. Even the range of output is relative
limited. Full-range dimming can be done only by pulsing the
LEDs and adjusting the pulse-width. If you do this at a high
enough frequency, it appears to be "flicker-free".

Even better - does anyone know of any LED lights suitable
for film that I could buy off the shelf here in the UK?

I have seen some theatrical lighting equipment that claims to
have LED sources, but as you say, they are scandalously
expensive.

Here's my dream LED light:

- dimmable from 0-100% with no change in colour temp
(ultimately I'd like to build in a remote control so I can
change dim the light whilst I'm looking through the viewfinder
on my camera)

With the price of the LEDs, the cost of the dimming parts of
the circuit (power transistors, heat sinks, etc.) will seem cheap.

- cheap!

Don't hold your breath. At least for a few more years.

- highly efficient

I seem to recall something about big heat-sinks on the backside
of the LED sources, and even fan cooling. Doesn't bode very
well for efficiency if all that power is going into useless heat.

- stable and predictable colour temperature (it would be very
cool if I could change the colour temp with a switch... my research
into LEDs so far has hinted at the possibility of changing the
colour temperature by increased in the current).

Doesn't seem likely. OTOH, people even make full-color image
displays with LEDs by close-spacing red, green, and blue LEDs
and pulse-width modulating them to produce any color you want.
"white LEDs" are sometimes nothing but red, green, and blue
LED chips in the same package. The colors combine to make what
appears to be "white" to us exactly the same as color displays
CRT, LCD, etc.)

Please do let me know your thoughts - any leads you can give
me will be very well received

In the last year or so, there has been a lot of discussion of white
LEDs and the circuits used to drive them from batteries over on
the newsgroup news:alt.binaries.schematics.electronic Dunno
about any of the other newsgroups you have cross-posted this to.

At least this is my perception of the current state of the art. I
would be happy to learn that there is better news.

I saw a Beyonce video ("Crazy in love" maybe) with a rooftop, twilight scene
with what looked like flat discs of white leds maybe a foot in diameter, a
bit like continuous ring-flash giving flat lighting.
I don't imagine the "non-flicker" is possible -about the only way to dim
LEDs is to use PWM - just hope the frequency is very much greater than your
line rate.
I'd agree that such lights are not likely to be cheap - there were probably
several hundred LEDs per disc/
My 2 cents

P.

 

[Stephen Neal]

Martin Underwood wrote:

"Daniel Kelly (AKA Jack)" <d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote in
message news:cl5mu4$g2e$1@uns-a.ucl.ac.uk...
[snip]

LEDs as film lights? Sounds highly intriguing. I thought that LEDs
tended to produce fairly monochromatic light, whereas you'd want
broad-spectrum white light for filming. Also, I can't imagine LEDs
producing sufficient light to illuminate something more than a few
millimetres away!

Have you seen many light entertainment shows recently? LED based coloured
effects lighting is everywhere these days.

You can get strips of single LEDs in a row, single miniature parcan-style
LED lamps, side lit panels and rows of LED discs. All of these can be
cycled in colour under lighting controller control - usually using DMX
data - allowing all sorts of multi-coloured effects. Pulsar Light are the
main manufacturers I know of who do this stuff.

Steve

 

[Tony Morgan]

In message <clap0q$kuu$1$8300dec7@news.demon.co.uk>, Stephen Neal
<stephen.neal@nospam.please.as-directed.com> writes

Martin Underwood wrote:
"Daniel Kelly (AKA Jack)" <d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote in
message news:cl5mu4$g2e$1@uns-a.ucl.ac.uk...
[snip]

LEDs as film lights? Sounds highly intriguing. I thought that LEDs
tended to produce fairly monochromatic light, whereas you'd want
broad-spectrum white light for filming. Also, I can't imagine LEDs
producing sufficient light to illuminate something more than a few
millimetres away!

Have you seen many light entertainment shows recently? LED based coloured
effects lighting is everywhere these days.

You can get strips of single LEDs in a row, single miniature parcan-style
LED lamps, side lit panels and rows of LED discs. All of these can be
cycled in colour under lighting controller control - usually using DMX
data - allowing all sorts of multi-coloured effects. Pulsar Light are the
main manufacturers I know of who do this stuff.

I've followed this thread with interest but not a little scepticism.
There seems to have been lots of references to high power *display*
LEDs. However, providing enough radiated light to give adequate
illumination for video filming seems to me a different issue. LEDs are
semiconductors, and semiconductors always have had serious problems with
heat dissipation and can so easily burn out (all those fans on the chips
in my PC - wow).

To get the equivalent of (say) a 500 watt flood in a LED (or even an LED
array) seems to be a bit of an extreme design concept and would seem to
have limited practical offerings compared with conventional lighting
units.
--
Tony Morgan
http://www.camcord.info

 

[Roderick Stewart]

In article <OyGULFGUwReBFwcL@zen54488.dircon.co.uk>, Tony Morgan wrote:

I've followed this thread with interest but not a little scepticism.
There seems to have been lots of references to high power *display*
LEDs. However, providing enough radiated light to give adequate
illumination for video filming seems to me a different issue. LEDs are
semiconductors, and semiconductors always have had serious problems with
heat dissipation and can so easily burn out (all those fans on the chips
in my PC - wow).

Touch an ordinary filament torch bulb while it is working, and then one of
those new high brightness white LEDs. Notice the difference. Filament lamps
are about 5% efficient, which means that for every 100W of light, you have
to dissipate nearly a couple of kilowatts of heat. I'm not sure what the
efficiency of LEDs is, but torches that use them run for months, so it must
be greater.

I see no reason why scaling this up for film or TV lighting use wouldn't be
possible, though producing acceptable colour rendition might be a different
matter, as the colour separation mechanisms used in photography assume a
uniform spectral characteristic of the light source.

Rod.

 

[Tony Morgan]

In message <VA.000007fb.01e235dc@escapetime.nospam.plus.com>, Roderick
Stewart <rjfs@escapetime.nospam.plus.com> writes

In article <OyGULFGUwReBFwcL@zen54488.dircon.co.uk>, Tony Morgan wrote:
I've followed this thread with interest but not a little scepticism.
There seems to have been lots of references to high power *display*
LEDs. However, providing enough radiated light to give adequate
illumination for video filming seems to me a different issue. LEDs are
semiconductors, and semiconductors always have had serious problems with
heat dissipation and can so easily burn out (all those fans on the chips
in my PC - wow).

Touch an ordinary filament torch bulb while it is working, and then one of
those new high brightness white LEDs. Notice the difference. Filament lamps
are about 5% efficient, which means that for every 100W of light, you have
to dissipate nearly a couple of kilowatts of heat. I'm not sure what the
efficiency of LEDs is, but torches that use them run for months, so it must
be greater.

While I see from the link that they do indeed exist, I'd argue that
efficiency should be tempered with cost ($4000 + with a lamp life of
2000 hours). If someone can afford the cost of buying, then they can
sure afford the cost of the power to drive them

Laurence (with his theatrical antecedents) will perhaps have some
insight into the relative cost of conventional lighting units.

I see no reason why scaling this up for film or TV lighting use wouldn't be
possible, though producing acceptable colour rendition might be a different
matter, as the colour separation mechanisms used in photography assume a
uniform spectral characteristic of the light source.

I see that the spec from the link gives 6000K, so I'd assume that colour
is not an issue. I also recall several years ago when tricolour LEDs
were used in reflective colour spectrometers for the print industry, so
I'd speculate that colour is an issue (or rather that any issues can be
relatively easily worked-around).
--
Tony Morgan
http://www.camcord.info

 

[Ian Stirling]

In sci.engr.lighting Roderick Stewart <rjfs@escapetime.nospam.plus.com> wrote:

In article <OyGULFGUwReBFwcL@zen54488.dircon.co.uk>, Tony Morgan wrote:
I've followed this thread with interest but not a little scepticism.
There seems to have been lots of references to high power *display*
LEDs. However, providing enough radiated light to give adequate
snip
Touch an ordinary filament torch bulb while it is working, and then one of
those new high brightness white LEDs. Notice the difference. Filament lamps
are about 5% efficient, which means that for every 100W of light, you have
to dissipate nearly a couple of kilowatts of heat. I'm not sure what the
efficiency of LEDs is, but torches that use them run for months, so it must
be greater.

Actually not.
LEDs are cooler because they have the heatsinks designed so they are cooler.
If they are not cooler, they stop working.
LEDs work very well at low powers.
Bulbs don't.

The current generation of white LEDs is about as efficient as a 500W
conventional floodlight bulb.

 

[Richard Crowley]

Just recieved in email from Video Systems Newswire...
(Additional online content at:
http://videosystems.com/mag/video_litepanels_lighting_kits/)

Will LEDs Light Your Productions?
Dan Ochiva

In Barry Braverman's review of the LitePanels Lighting Kit in September's
Video Systems, the author praised the company's LED-based on-camera light as
an ideal solution for DV'ers. Braverman said the far more efficient LED
device bested tungsten-based gear in delivering a dimmable, daylight color
value along with higher output than traditional on-camera lights.

There are great benefits, it turns out, if you dump today's tungsten and
halogen lighting technology. Those lamps heat their light producing metals
and gases in such an inefficient way that some refer to them as heating
devices that happen to give off light.

Another strike against tungsten and halogen lights? They need heavy
capacitors and transformers to change AC to DC and filter out the AC pulses.
Such power supplies--which must provide continuous, always on wattage--are
heavy, bulky, and expensive.

But LEDs are different. Light emitting diodes are solid state electronic
devices. They use a pulsed, switching power supply similar to the one in
your computer.

More benefits come from combining an LED and a switched power supply. A
microprocessor, for example, can be used to precisely dim an LED.

LEDs also just keep on working. Some companies claim up to 100,000 hours of
useful life for their LEDs, albeit in a laboratory setting.

Those are some of the reasons that make LED-based systems such as LitePanels
such a production breakthrough. But don't think you can slap one together
after a trip to Radio Shack. It's trickier than that. For example, to
achieve the light's useful 80 footcandle (or lumen) output, a LitePanel is
studded with 140 small, carefully positioned LEDs, with a microprocessor
controller onboard too.

This new approach to lighting, says Braverman, enables shooters "to take
control of our craft, and the extraordinary LitePanels system can help us do
precisely that."

But if the benefits are so great, why can't we use LEDs for production
lighting to replace those hot, clunky lights we use today? Complexity is one
reason. Remember, it takes 140 tiny LEDs precisely fitted into a 6.75 x
2.25-in. form factor to create a LitePanel.

To make a system bright enough to light a set would only result in a pricey,
complex, and fragile light. Heat too becomes a problem with that many LEDs.
While LitePanels' smaller light array doesn't generate much heat, placing
thousands of closely spaced LEDs together would create enough heat to melt
the whole thing.

But a new generation of super bright LEDs will soon change that. One of the
leaders in developing and manufacturing these new LEDs is San Jose,
Calif.-based Lumileds. The company says its Luxeon V Star LEDs are the most
powerful LED light sources available.

How bright? The company says a single Luxeon V Star lights delivers 37
lumens at 1 amp, drawing only 3W of power. (Stats are from the Lumileds web
site.)

Considering that the current LitePanel needs 140 LEDs to deliver 80
lumens...well you can see there's quite a jump in capability. The Luxeon is
specified for AC or DC 12V operation, which means one bulb can be used in
existing low voltage halogen lighting systems.

The brightness of Lumileds' Luxeon opens up new uses. In August, the company
announced that Sony chose Luxeon lamps for its top of the line Qualia 05 LCD
televisions. The lamps, installed in the Triluminous backlight, replace the
fluorescent lighting used by most LCD displays. The companies worked
together to develop a system suitable for the task, with results claimed to
deliver the highest color gamut. While conventional fluorescent/LCD
combinations reproduce only 65-75% of the NTSC color space, the Qualia 005
delivers a color gamut claimed to be 105% better than the NTSC color space.
(At press time, no one was available to explain that extra 5%.)

A smaller version of the lamp will even turn up in a new generation of
camera phones, due to roll out over these next few months. The two models
deliver either 40 or 80 lumens, said to be 12 times brighter than standard
mobile phone flashes.

Heat, however, becomes a problem when running this new generation of LEDs en
masse. "What heat?" you may ask. But these aren't the standard sort of LEDs;
those are meant to be looked at directly, which means they don't use much
power at all. These pop up everywhere, in signs, stoplights, and the front
panel of your stereo.

However, to light an object, LEDs need to be able to push through much more
power. While the lamp itself is only about 1mm in diameter, each uses
anywhere from 1 to 5 watts. Even a 1 watt LED, if not properly fitted into a
heat sink, gets hot.

In October, Westhampton, New Jersey-based Lamina Ceramics announced a
solution, one which will allow the creation of much larger light arrays that
could be useful in production.

Lamina doesn't make the high-power LEDs itself. Instead, this Sarnoff Labs
spin-off created a method to bond hundreds of LEDs to a single heat sink. It
works, to an extent. Their pioneering disk array design cuts some of the
output of the super bright LEDs, while sucking up much more energy than
expected. The cost is a shocker too: $4900, though that's not a bad price
for fixed installations used in theaters, for example, which will appreciate
the light's long lifetime.

That 5-in. diameter disk, though, delivers some 13,300 lumens. Wow.

You can get your hands on this new generation of LEDs, but not immediately.
LitePanels has a number of high-brightness lights nearing design completion.
This means that they're on schedule to release by NAB 2005.

The new on-camera/camcorder light will use only five high-output LEDs,
sourced from another company than Lumileds, says Steve Gillette, product
manager for the LitePanel.

"We're also planning a high-output IR (infra-red) model," says Gillette.
"For general production lighting, expect to see a 12-in. x 12-in. unit
that's only about 2-in. thick. You'll be able to interlock these to create
large grids, or mount them on a C-stand."

Gillette promises that the costs will be "affordable" and the heat bearable.

That's a relief. You might soon be able to fire that 'ol quartz lamp,
instead of firing it up.

 

[Tim Shoppa]

"Richard Crowley" <rcrowley7@xprt.net> wrote in message news:<10nkqu21d3hag05@corp.supernews.com>...

Just recieved in email from Video Systems Newswire...
(Additional online content at:
http://videosystems.com/mag/video_litepanels_lighting_kits/)
Another strike against tungsten and halogen lights? They need heavy
capacitors and transformers to change AC to DC and filter out the AC pulses.
Such power supplies--which must provide continuous, always on wattage--are
heavy, bulky, and expensive.

But LEDs are different. Light emitting diodes are solid state electronic
devices. They use a pulsed, switching power supply similar to the one in
your computer.

There's no fundamental reason why a switching power suppply couldn't
be used with incadescent lights. But they're missing what works so nicely
with LED's: PWM to control intensity with very little color shift
as intensity changes. And with RGB arrays and RGB sensors and feedback the
ability to make color shift from heating in the LED array a complete
non-issue.

More benefits come from combining an LED and a switched power supply. A
microprocessor, for example, can be used to precisely dim an LED.

Again, they're missing the fundamental point of PWM with LED sources.
After you take LED heating into account you need a feedback loop anyway
to regulate brightness to more than 30% precision (so you need more than just
a microprocessor, you need a sensor and a loop too) as the array heats
up and cools down.

Tim.