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Josie Williams

Heat proofing lights/ heat filters

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Hi all,

 

I'm attached to a project shooting in a listed building (very old house in the UK with antiques) and one of the specifications is that I can't use hot lights as they may damage paintings and antiques in the house.

 

I've been told about using heat filters on lights, just wondering people's experiences/opinions of them.

 

Thanks

 

Josie

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Hi Josie,

 

Heat filters or Dichroic mirrors as they are sometimes called just divert the heat from the beam to not from the beam....

But you still get the heat in the room unless you have some clever extraction system.

 

The only answer is to use as few conventional tungsten as you can get away with and use fluorescent or LED for the bulk of the lighting.

These are far more efficient and generate much less heat than tungsten.

 

Sales Pitch Warning - visit www.photonbeard.com for a full choice of lighting instruments.

If you are looking to buy there are plenty of dealers in the UK and if you are looking to rent then we also have a good selection all within the buy/rent section.

 

Depending on what you are shooting you could get away with a small of our LED Redheds or you may need something bigger like our fluorescent Highlight range. If you need lots of light coming through a window then our Platinum Blonde HMI is the answer.

 

Regards

 

Pete

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Thanks Pete,

 

I was actually suggesting Photon Beard's LEDs to the DoP the other day, I was very impressed by your range at BSC and BVE this year.

 

Will show to DoP when we have our next meeting and perhaps he and I could come and view some?

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Great news,

 

Happy to host you at the showroom in Leighton Buzzard anytime you want to check out the range.

Just drop us an email or give us a call.

 

if the DoP brings his camera along he can check out the image quality.

 

Regards

 

Pete

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there is "heat shield" which is a thin clear gel almost like cellophane. as said it only diverts the heat so its good to protect things for example if you have a large light near a window you often use it to stop the light from getting to hot and breaking the glass.

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I was actually suggesting Photon Beard's LEDs to the DoP the other day, ....

 

If the purpose of the production is to showcase the art and antiques in the house I would not use LEDs without first conducting extensive camera tests. The problem you are likely to encounter using LEDs is that, given the discontinuous nature of their spectral output, LED fixtures are simply not capable of rendering colors accurately. You will get much more faithful color rendering from tungsten lamps with heat-shield on them, then you will get from LED lamps.

LED_Model_Comp.jpg

Left: Tungsten source, Right: White Phosphor LED source.

 

This inability of LEDs to render color accurately is very visible in make up, wardrobe, and props tests performed by The Academy of Motion Picture Arts and Sciences (AMPAS) as part of their “Solid State Lighting Project Technical Assessment.” (use this link for details.) In one (above) a model was photographed wearing a dress that had a number of different blue tints. Footage was shot with both a true tungsten source and a 3200K LED source. The tungsten-lit footage displayed all of the subtle differences in blue tones in the fabric, while the LED-lit footage, lacking cyan output, showed just a nice blue dress, without the same richness of hue. Since the light doesn’t put out much cyan, the camera/film simply can’t record it.

 

The same holds true of flesh tones illuminated by LED light. As is also evident in the pictures above, skin tones don’t reproduce well under LED lights because of the steep drop off of high frequency colors (above the 600nm cut off) such as pinks, reds, oranges, and other long wave-length colors. As the illustration below, comparing the reflected spectral distribution of a Caucasian skin tone under theoretical pure white light (an even distribution of all wavelengths) to that of a 3200K LED demonstrates, absent these wavelengths the skin tones look pale under LEDs because light reflected by the skin tone is likewise absent these critical long wavelength colors.

 

 

LED_Effect_on_Skin_Color.jpg

Reflected Spectral Distribution of Caucasian skin tone under theoretical White Light and Phosphor White LED Light

 

 

In the picture above illuminated by a 3200K LED, both the cyan/blue dress and the skin tone, don’t reproduce well because you can't get accurate color reflected from an object unless that color is in the light in the first place. In other words, if the light source doesn’t generate the color (cyan), it is not reflected by the object (the dress) and so the camera/film simply can’t record it.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston

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I don't disagree with anything Guy has said there.

 

But our LED is a remote phosphor unit which scores very high on the TLCI (Television Lighting Consistency Index).

See here for more details - http://www.gtc.org.uk/tlci-results.aspx

TLCI in a much better way of checking for colour consistency that CRI which is faked to give a high reading

 

Peter Daffarn

MD

Photon Beard

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We have no images of the location, size of the rooms, ceiling height, architectural obstacles, etc., so.......

I can't see why using a selection of Kino fixtures wouldn't work.

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But our LED is a remote phosphor unit which scores very high on the TLCI (Television Lighting Consistency Index).

 

I took a look at the TLCI results for the Photon Beam LED with 3200K remote phosphor panel available on The Guild of Television Cameramen website. While the color rendering is an improvement over that of a Phosphor White LED, it suffers from the same shortcomings and is still marginal.

 

If you compare the Spectral Power Distribution Graph for the Tungsten Photon Beam to that of a Phosphor White LED, they are similar and in no way resemble that of a true black body radiator like a Tungsten filament. The inherent limitation to the “Stokes shift” process by which a portion of a “pump” color is transformed from shorter wavelengths to longer wavelengths in Remote Phosphor LEDs is that it works in only one direction – that is why Remote Phosphor LEDs don’t emit color wavelengths shorter than their pump color. Another, inherent shortcoming to this approach to generating “tungsten” light from an LED is that there is a tradeoff between lumen output and warmer color temperatures (see my newsletter article for details.)

LED_Photon_Beam_SDG.jpg

 

The Tungsten Photon Beam clearly suffers from these limitations. If you compare the spectral distribution of its light output (the black trace above) to that of a Tungsten filament (the cyan trace above), the output of the Tungsten Photon Beam drops off steeply below its pump color (which is at 450nm verses 465nm of the Blue LED used in typical Phosphor White LEDs) so that it puts out no wavelengths below 400nm. By comparison a Tungsten filament continues to generate light with wavelengths well below 400nm which is why tungsten light will render violet colors better. While the Tungsten Photon Beam appears to generate more light in the medium blue-cyan-turquoise range from about 465-510nm than the typical Phosphor White LED, it is still much less than a tungsten light which is why these colors don’t reproduce as well either. Finally, its’ long-wavelength cutoff is still at about 625 nm where a tungsten filament continues to generate light all the way out. Because of this rapid drop off of wavelengths above 625nm, pinks, reds, oranges, and other long wave-length colors look dull under the Tungsten Photon Beam, compared with how they look under a Tungsten source which continues strong all the way out on the long-wavelength end.

 

Even by the TLCI rating system the output of the Tungsten Photon Beam is marginal and will require color correction in post in color critical projects like this. Yes, tungsten heads consume a lot of power and generate a lot of heat (which can be directed away from sensitive artifacts with heat shield) but they will render color faithfully. I guess the question comes down to whether you want to get the colors right in the camera or pay a colorist to fix it in post.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston

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Even by the TLCI rating system the output of the Tungsten Photon Beam is marginal and will require color correction in post in color critical projects like this. Yes, tungsten heads consume a lot of power and generate a lot of heat (which can be directed away from sensitive artifacts with heat shield) but they will render color faithfully. I guess the question comes down to whether you want to get the colors right in the camera or pay a colorist to fix it in post.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston

 

 

Sometimes I wonder 'why bother'... Dulwitch Picture Gallery in London put up a chinese 'fake' of a master painting, then asked patrons to 'identify' the fake. Apparently only 10% of those responding to the test, did so correctly...

 

Here's the two works... which is the fake for $120... and which is the original, perhapsworth perhaps millions...

 

2fbd579f0a7eea2801028c100732419f.jpg

 

4f1ddbf540b4a8d67ddf4141c85df8c0.jpg

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The first one is fake, what do I win? I don't see how this is applicable to the OP's question.

Edited by JD Hartman

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The first one is fake, what do I win? I don't see how this is applicable to the OP's question.

 

The first one is the original...

 

But there was a certain amount of irony in the thread in regard to getting lights that allow for accurate recording, yet, in the case of the 'fake', most casual viewers couldn't identify the fake.

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I though this thread was about lighting the project without excessive heat that might damage the premises and artifacts?

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I though this thread was about lighting the project without excessive heat that might damage the premises and artifacts?

 

That would have been taken care of by using say and LED lamp, with sufficient lumen output... but due to the need for maintaining the quality of light, hence tungsten, hence need for heat protection.

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The first one is the original...

 

But there was a certain amount of irony in the thread in regard to getting lights that allow for accurate recording, yet, in the case of the 'fake', most casual viewers couldn't identify the fake.

 

I don't think whether people can spot a fake painting or not is pertinent. Nor is whether they can objectively discriminate (tell the difference between) a tungsten source vs a modern source with some deficient spectra. Culture, which includes film (even digital) media should culture human experience, not exploit its deficiencies in the objective domain.

 

We may not respond objectively to strange gaps in the spectrum, but we will be absolutely responding on a direct neuro-physiological level. Of course, if you have no conscience at all you can teach people not to sense this difference. Make them dull. Culture them to see less. A crime, and a bizzar irony I think.

Edited by Gregg MacPherson

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LED is the way to go. The remote phosphors are very trainee colour wise. Talk to Pat at Green kit film lighting - he basically specialises in LED, used to work at Lees, left when it went to Panalux.

 

He's got a pretty substantial selection of units and can advise you on colour quality - nice guy too and good value

http://www.greenkit.london

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LED is the way to go.

 

Not necessarily. Even if the focus of this production was not the artwork or antiques in the house, but the house was only serving as the set of a period drama, there are good reasons not to use LED fixtures. Another problem with LEDs (remote phosphor included) is that color correction gels are not calibrated for their discontinuous spectrum and so you get unexpected results from their use on LEDs. This is because certain parts of the color spectrum simply are not present in the light they emit, while there is an overabundance of other parts of the spectrum compared to the light source for which the gels were designed. This problem is further compounded by the fact that white LEDs are simply blue LEDs with a phosphor counting. This presence of a strong blue light base has a huge impact on their color rendering and the way in which colot gels affect their output. For example, you know what to expect when you put a color correction gel, say ¾ CTO, on HMI or Tungsten lights, you don’t know what you will get putting that same gel on an LED light. The reason is that because of their discontinuous spectrum, the use of CC gels on LEDs have unintended and undesirable consequences.

 

LED_CC_34CTO_Day_Conv.jpg

3/4 CTO gel passes only certain wavelengths (represented by the spectral transmission curve (center)) of daylight (left) to create the color spectrum approximating that of a 3200K tungsten light (right.)

LED_CC_34CTO_LED_Conv.jpg

The same 3/4 CTO gel applied to a daylight LED (left) passes the same wavelengths (represented by the spectral transmission curve (center)) to create an unknown color spectrum that does not approximate a 3200K tungsten light.

 

A good example of this is what happens when you try to convert the 5500K out-put of Phosphor White LEDs to 2900k with Full CTO gel. Where you can do it with some success with HMIs because there are long wavelengths in it’s continuous spectrum to pass disproportionately to the blue part of the spectrum to achieve a nominal 2900K, since LEDs don’t put out much beyond 625nm, there is not much for a filter to pass to rebalance the light output to 2900K, so the “corrected” light is too cool.

 

Another undesirable consequence comes from the fact that Full CTO is designed to pass extra green (there is a bump in the spectral transmission curve of Full CTO in the green portion of the spectrum) and so it creates, given the amount of green inherent in Daylight LEDs to begin with, a disproportionate amount of green (creating an overall green bias) to the "corrected" light when used on Phosphor White LEDs ( link to test results demonstrating this with a Lightpanel 1x1 Daylight Spot.) The gel pack that eventually made the Lightpanel 1x1 Daylight Spot in the test marginally similar to a tungsten light, was only able to do so at the expense of two stops – so much for the greater efficiency of LEDs.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting & Grip Rental and Sales in Boston

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We're aware of the problems, Guy. The thing is, the cheaper alternatives have problems too. Tungsten consumes so much power that many shoots couldn't happen if that's all we used. It creates enormous amounts of heat. It becomes even more woefully inefficient when you convert it to daylight.

 

Right now the question is not so much why use LED, but why not use HMI, given that LED of any quality is of a similar price.

 

It is worth bearing in mind the filtration issue, though. Conventional colour temperature correction filters are designed to work on tungsten and other high-CRI sources. As Guy says, while they should work reasonably well on anything with reasonable colour rendering, they can create complicated problems when used on discontinuous-spectrum lighting. Conventional CTO and CTB are not likely to work well on LED, but then they don't work very well on kino-flos either.

 

P

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Guy, I'm with you on the tungsten. In terms of light quality tungsten is very reliable. But it's not without it's issues as Phil points out.

 

I said LED because the OP specified you can't use hot lights - and HMIs run hot.

 

I did try posting again to day 'or light from outside' in which case the temperatures of the light fixtures themselves aren't an issue and the light output of HMIs is cooler (and the heat filters might be an option for tugsten units outside - assuming you have the power needed to use I units powerful enough to make a difference coming from outside).

 

In terms of CRI / well, HMIs and fluorescents are petty awful in that regard too (and likewise discontinuous). What HMI has going for it is power output: if you need punch LEDs just don't cut it. Of course you still have to issue of reliability of supply (which is not always great in these old houses)

 

But if the issue is working *within* a climate controlled environment then then you need to work with lights that run cool - which means LED or fluorescent - and if you want something focusable, that means LED. If you want something with reasonably reliable colour and decent dimming that also means LED (flouros are pretty crap in that regard - unless you're a fan of magenta) - and within the output ranges available they're pretty energy efficient too: you can run most LED units off a battery (which deals with unreliable supply)

 

Horses for courses.

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Sales pitch warning

 

We just had this video released to us for our own use. It was not made by us, in fact we only knew about it when it was complete and ready for publication.

It does cover many of the questions raised in this thread so I thought it appropriate to link it here.

 

Sorry if this is wrong but I did clearly start the answer with a warning.

 



 

Peter Daffarn

MD

Photon Beard UK

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It does cover many of the questions raised in this thread so I thought it appropriate to link it here.

 

This video clearly demonstrates the point I was trying to make above. The reason the flesh-tones in this demonstration video look so pasty is that LEDS, including Remote Phosphor types, put out very little light beyond 625nm where a tungsten filament continues to generate light all the way out.

LED_Photon_Beam_SDG.jpg

 

Because of the rapid drop off of wavelengths above 625nm in the spectral distribution graph above for the Tungsten Photon Beam 80, pinks, reds, oranges, and other long wave-length colors look dull under the PB80, compared with how they look under a Tungsten source which continues strong all the way out on the long-wavelength end. This is very clear in the red and magenta MacBeth Chart swatches for the Tungsten PB80 below.

LED_Photon_Beam_Red.jpg

LED_Photon_Beam_Magenta.jpg

 

As is evident in these swatches from the TLCI test results for the PB80, the red rendered by the PB80 (the inner square) is dull by comparison to the vibrant red rendered by tungsten light (the outer square.) Lacking vibrant long wavelength colors flesh-tones rendered by LEDs lack vitality. Yes, tungsten heads consume a lot of power and generate a lot of heat but they render healthy vibrant flesh-tones.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston.

  • Upvote 1

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But if the issue is working *within* a climate controlled environment then then you need to work with lights that run cool - which means LED or fluorescent - and if you want something focusable, that means LED. If you want something with reasonably reliable colour and decent dimming that also means LED (flouros are pretty crap in that regard - unless you're a fan of magenta)

 

Not necessarily. If the issue is heat projected by a light onto delicate artwork, he can use heat-shield in front of the lamp. If the issue is raising the ambient temperature of the room, he can use a portable room air conditioner to keep the room from becoming too hot. There are better solutions than using LED sources.

 

Even if the OP was willing make do with less than accurate color rendering, the bigger problem IMO is that gels are not calibrated for the discontinuous spectrum of LEDs and so you get unexpected and undesirable results from their use on LEDs. A good example of this is what happens when you try to convert the 6500K out-put of LEDs to 3200k with Full CTO gel. Where you can do it with some success with HMIs because there are long wavelengths in it’s more or less continuous spectrum to pass disproportionately to the blue part of the spectrum to achieve a nominal 3200K, since LEDs don’t put out much beyond 625nm, there is not much for a filter to pass to rebalance the light output to 3200K, so the “corrected” light is too cool.

LED_CC_Full_CTO.jpg

 

As indicated by the its' spectral transmission curve, Full CTO passes a disproportionate amount of the green portion of the spectrum.

 

Another undesirable consequence comes from the fact that Full CTO is designed to pass extra green (there is a bump in the spectral transmission curve of Full CTO in the green portion of the spectrum) and so it creates, given the abundance of green inherent in Daylight LEDs to begin with, a disproportionate amount of green (creating an overall green bias) to the "corrected" light when used on 6500K LEDs (use this link to see more color tests.)

 

LED_Tungsten_Vs_Corrected_LED_Sm.jpg

Left: Tungsten lit scene with Lee 147 Apricot gel on backlights and no gel on side lights. Right: Daylight LED lit scene with Lee 147 Apricot on backlights and side lights corrected to 3200K with Lee 204 Full CTO. Note greenish cast to corrected LEDs.

 

To remedy this problem of remote phosphor LEDs, the Photon Beam 80 has a 3200K color correction (CC) phosphor panel to use in place of Full CTO, but it lacks the intermediate grades of color correction like ¾, ½, and 1/8 CTO that are frequently used to create a warm daylight effect with HMIs. And, since the conventional approach to creating moonlight with a 3200K balanced camera/stock is to put ½ CTO on HMIs, the absence of a 4300K color correction phosphor panel is a major drawback IMO.

 

Other manufacturers like Cineo make partial CC phosphor panels available, but at a cost well over $200/panel they are an extremely expensive alternative to a $6.50 sheet of gel. Not only are the CC phosphor panels extremely expensive, but the choice is limited to just CC equivalents to the CTO gel series. So if you are like me, and prefer to use Half CTS (Color Temperature Straw) rather than Half CTO to create warm sunlight because it is less orange, than you are out of luck. Likewise, if you want to use any of the hundreds of color gels that are available because the blue light spike that is present in LEDs, but not in Tungsten or HMI lights, means that the resulting color will be unpredictable and possibly undesirable. The OP doesn’t have to compromise his color and creativity.

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Rental & Sales in Boston

  • Upvote 1

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Guy, thanks for all the tech. info. you publish. The dress in the image on the right certainly has a green cast to it.

 

Perhaps I've missed some critical requirement in the original post. Why can the OP use a selection of Kino fixtures for his shoot?

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gels are not calibrated for the discontinuous spectrum of LEDs and so you get unexpected and undesirable results from their use on LEDs

 

Yes, so, you, er, shouldn't do that.

 

P

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