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Cutting through the hype surrounding Light Emitting Plasma (LEP) lamps


Guy Holt
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Light emitting Plasma, or LEP, is getting a lot of press lately. However, you have to be wary of all the claims made by head manufacturers. Whenever a new lighting technology comes on the market, the manufacturers put a little spin on the scientific data (LED manufacturers do this still), which has a tendency to cloud issues. For this reason, to pick the right LEP luminary for a particular job it helps to have a little knowledge of the technology. For our company newsletter I have put together an overview of the technology and what products are available for motion picture lighting (available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20LEPs.) In this newsletter article I have tried to cut through some of the hype. Here is a quick summary of a few of the issues.

Plasma_STA40_Features.jpg

 

Yes, LEP bulbs are capable of intense light output. One manufacturer, Luxim, claims their technology can produce 144 lumens per watt. In contrast, Tungsten Halogen bulbs produce 15 lumens per watt, LED emitters produce between 65 to 85 lumens per watt (in practical applications), and HMI bulbs produce 90 Lumens per watt. While there is truth in this claim as it pertains to an LEP bulb in isolation, as with LEDs, manufacturers have not realized anything close to that kind of lumen efficiency within the framework of a practical light that will burn in all lamp orientations.

 

Plasma_Helio270LG.jpg

The Helio 270 LEP

 

When the pill sized LEP bulb in mounted in the “puck” so that it will burn in all head orientations, the emitting area is no more than 1/4" x ¼." In this configuration, the 273W LEP bulb will deliver 16000 lumens or 57 lumens per watt. While much less than the 37’000 lumens the bulb will generate fully exposed in a horizontal position, it cannot be tilted up in that orientation. On the plus side, mounted so that it will burn in all orientations, all of its’ output is forward directed within a 60 degree angle so it doesn’t require a reflector. Such a highly localized forward directed light is ideal for Fresnel type instruments. As close an approximation to the ideal point source that exists today, its light output favors the central portion of the Fresnel lens. Since, this part of the lens has greater transmittance, LEPs are a more efficient source for Fresnel type heads than tungsten filaments, LED arrays, and even HMI arcs. For this reason you get more of those lumens transmitted through the lens in a highly collimated light that is very clean and crisp making it great for cutting shadows or gobo effects. The 273W LEP bulb in a Fresnel type instrument has an output comparable to a 575W HMI Fresnel.

 

Plasma_Forward_Projection.jpg

Forward directed output of Helios 270 LEP

 

LEP head manufacturers also claim that LEP lamps provide a CRI of 94+. While impressive, CRI ratings published by manufacturers can be misleading. Where the CRI index indicates the ability of a light source to reproduce to the eye only 8 colors faithfully (a different 8 colors are used in Europe) they should be taken with a certain amount of skeptism. In the case of LED luminary manufacturers, for instance, it is possible to tune their output to the limited color range of the CRI color scale and deliver good color rendering to the eye while delivering generally poor color reproduction on the screen.

 

Plasma_vs_Mole_LED.jpg

 

More important than their high CRI ratings, is the fact that LEP lamps generate light with a continuous color spectrum. If you compare the spectral power distribution graphs (above) of natural daylight and LEP lamps (available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20LEPs) you see that, except for very brief drop outs at approximately 425 nm and again at 475 nm, the light output of LEP lamps is almost identical to natural daylight.

 

And, as also can be seen in their spectral distribution graphs above, Plasma lamps have a much more continuous color spectrum than even the best LED luminaries on the market today. For instance, LEP lamps, unlike LED lamps, generate light at wavelengths shorter than 425nm - which means that violet colors will render better. And, unlike LED lamps, LEP lamps also output in the medium blue-cyan-turquoise range from about 465-510nm so aqua-type colors render well by comparison. Skin tones and warm, amber-yellow colors stand out better under LEP lamps because of the strong presence of their complementary colors. And, since the output of LEP lamps extend all the way out on the long-wavelength end (well beyond the 600 nm cutoff of LEDs), pinks, reds, oranges, and other long wave-length colors look vibrant under LEP light where they tend to look a little dull under LEDs. As a continuous spectrum source, colors not only appear more natural and vibrant under LEP lamps than under LED lamps, they also reproduce more accurately on the screen since, as is also evident by their spectral distribution graph, the output of LEP lamps is almost an exact match to the spectral sensitivity of daylight film emulsions and digital sensors. Plasma lights will deliver the same true-to-life color rendition previously achievable only with full-spectrum Daylight or HMI sources. As an added bonus, color meters, like the Minolta III F, that make their calculations of the Color Temperature (CT) based on a light sources continuous spectrum, are able to generate accurate reading of the CT and Green/Magenta of LEP lamps where they are almost completely useless with LEDs.

 

Another feature of LEPs that has been overblown is their purported 20-30’000 hr lamp life. But, where I am out of space here, I will pick up with that issue in my next post.

 

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

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Another feature of LEPs that has been overblown is their purported 20-30’000 hr lamp life. But, where I am out of space here, I will pick up with that issue in my next post.

 

What is the “lamp life” of an LEP bulb is up for debate. Peter Daffarn of Photo Beard wrote in the Cinematographer’s Mailing List (CML): “Lamp life as quoted by Luxim is 30,000 hours but we are saying 20,000 to be sure.” Such claims of 20'000 – 30’000 hr lamp life made by manufacturers like Photon Beard should be taken, I think, as nothing more than marketing hyperbole. Determining the "life" of an LEP, like that of an LED, is a very complex matter because LEPs have no filament or electrodes to burn out and thus will keep on producing light, although at declining levels and with a gradual shift in color, beyond their useful life. And, since a LEP (like an LED) has a comparatively very long life (as conventionally defined), over which its' lumen output drops continuously, it also has an appreciatively greater lumen depreciation over that life than does an HMI lamp. Given their continuous lumen depreciation and color shift over time, it is clear that there comes a time when a LEP bulb has surpassed its’ working life and should be retired. Since it won't burn out in its' prime, like an HMI lamp, how do we determine when a LEP has surpassed its' useable life.

 

Plasma_Color_Shift_Alt.jpg

 

 

Clearly, this new technology requires a new approach to determining useable "lamp life" than that used for conventional lamps like HMIs. For instance, how useful is Photon Beard’s "lamp life" of 20'000 hours when according to Luxim’s specifications the bulb’s lumen output will depreciate as much as 60% with a color shift of 1000K (from 5300K to 4300K) in that time. Whatever the stated lifetime of any emitter technology, it must reflect a meaningful statistical measure of the performance of it in a given fixture design for a specific application. Clearly, in the case of LEP luminaries to be meaningful "lamp life" must be defined as the point of unacceptable lumen depreciation and color shift for our particular application rather than complete failure to light. And, whatever level of lumen depreciation is chosen for “low-light failure”, to be meaningful to it's users, it should be in line with existing lamp technologies used in that industry.

 

Plasma_Decay_Alt.jpg

 

In the case of motion picture lighting, I would argue that nothing short of a L85 criteria would be appropriate and meaningful, since that has been our experience with both HMI and Tungsten Lamps (where the “rated life” is the interval in which 50% of lamps fail and with an average lumen depreciation of 80-85%.) If we adopt this criteria for motion picture lighting applications of LEPs, their rated lamp life would still be an unparalleled 5000 hrs (compared to 500-750 hrs for HMIs and approximately 1500 hrs for LED fixtures.) In other words, the interval in which the output of an LEP drops-off of to 85 percent of its’ original value (L85) is 5000 hrs. Unlike an LED fixture that has no replaceable parts, the bulb of an LEP can be replaced after reaching this “low-light failure”, so the fixture does not have to be thrown away as is often the case with LEDS (see newsletter article for details.)

 

Where we are a long way off from having a single-die LED with sufficient output and correlated color temperature to match HMIs, LEP lamps are a cost effective alternative to expensive HMI Fresnel systems when it comes to generating daylight balanced light. In fact there is one LEP head that we are looking at (not the Photon Beard Nova 270 – it’s too expensive) because it has a Power Factor of .99 making it a near linear load. As a result, it uses power more efficiently, minimizes return current, and generates virtually no line noise. Where, it is as much the Harmonic Noise that non-PFC HMI, Fluorescent, and LED power supplies kick back into the power stream, as it is their higher Apparent Power, that limits the total number of them that can be reliably operated on conventional portable generators; the efficiency and near unity Power Factor of this LEP head means that you can operate more of them on portable gas generators. For instance, you can operate four 575W HMIs on a 6500W portable AVR generator, where you should be able to operate 23 of these 270W LEP heads (each with an output comparable to a 575W HMI).

 

Plasma_PowerWaveform.jpg

Oscilloscope shots comparing the current and voltage waveforms of the PFC Helio 270 with an equivalent wattage of non-PFC LEDs

 

Where LEP is radically new technology there is a lot to get your head around. One way to think of a LEP bulb is as a tiny discharge lamp. But, unlike an HMI bulb it does not have electrodes. Instead of applying a voltage and drawing a current through the lamp to create light as does an HMI, the energy that creates light in an LEP comes via a high frequency RF transmitter. The RF waves heat the materials inside the lamp and bring those materials to a plasma state so that the lamp emits a "flicker-free" light. Besides better color rendering, light quality, and lamp life, this different method of transforming electricity into light has other benefits as well. For more details about LEPs see our newsletter article at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20LEPs.

 

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

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Yeah! But are they any good Guy?:-)

 

Once you cut through the hype, the bottom line is that LEP heads offer a number of advantages over LED & HMI technology. Where we are a long way off from having a single-die LED with sufficient output and correlated color temperature to match daylight, LEP lamps are really the only cost effective alternative to expensive HMI Fresnel systems when it comes to generating full spectrum daylight balanced light. This feature of LEPs benefits Red users and DSLR users in particular.

 

One downside to lighting for the 5000K native color balance of CMOS sensors in the past has been that it requires an all 5000K balanced lighting package and HMIs are considerably more expensive to buy or rent than other light sources. Kino Flo fixtures, particularly the Parabeams, are a cost effective alternative to HMIs because they can use either 3200K or 5500K tubes. But, the drawback to fluorescent fixtures (like LED fixtures) is that they generally have a very broad soft light output that drops off rapidly which means the units need to be positioned close to the subject they are lighting. This characteristic has always made them better suited to lighting documentary interviews than dramatic scenes.

 

With a 5300K output comparable to that of a 575 HMI Fresnel, the Helio 270 Plasma lamp in particular offers the same benefit of being a less expensive alternative to HMIs, but also offers the added benefit of being more versatile than a Kino Flo or LED light panel. Not only does it offer the capacity of traditional Tungsten/HMI Fresnels to throw and control its light output (making it a more suitable Key and Backlight source for lighting dramatic scenes), but it also has sufficient output to bounce it or waste some output to diffusion material to make it softer (existing LEDs put out barely enough, with none to waste.) It’s capacity to provide both hard crisp light that will throw a distance and is easily controlled, as well as offer soft light with diffusion, makes the Helio 270 much more versatile than any Fluorescent light or LED array presently available. It also offers a number of benefits that the new LED Fresnels and traditional HMI Fresnel do not.

 

For instance, LEPs do not require the active microprocessor color control that is required to assure consistent color rendition in the best LEDs on the market today. Absent such microprocessor based color management systems, LEPs are less expensive and more robust than LEDs. Plasma lamps also have a much more continuous color spectrum than even the best LED luminaries. As is evident in the Spectral Power Distribution graphs below, LEP lamps, unlike LED lamps, generate light at wavelengths shorter than 425nm - which means that violet colors will render better.

 

Plasma_vs_Mole_LED.jpg

 

And, unlike LED lamps, LEP lamps also output in the medium blue-cyan-turquoise range from about 465-510nm so aqua-type colors render well by comparison. Skin tones and warm, amber-yellow colors stand out better under LEP lamps because of the strong presence of their complementary colors. And, since the output of LEP lamps extend all the way out on the long-wavelength end (well beyond the 600 nm cutoff of LEDs), pinks, reds, oranges, and other long wave-length colors look vibrant under LEP light where they tend to look a little dull under LEDs. As a continuous spectrum source, colors not only appear more natural and vibrant under LEP lamps than under LED lamps, they also reproduce more accurately on the screen since, as is also evident by their spectral distribution graph, the output of LEP lamps is almost an exact match to the spectral sensitivity of daylight film emulsions and digital sensors. An added benefit to LEPs is that color meters, like the Minolta III F, that make their calculations of the Color Temperature (CT) based on a light sources continuous spectrum, are able to generate accurate reading of the CT and Green/Magenta of LEP lamps. Color meters are completely useless reading the “spiky” discontinuous color spectrum of LEDs (see my newsletter article for details .)

 

The biggest benefit to LEPs in comparison to HMIs has got to be the cost savings in not having to replace lamps every 500 - 750 hrs as is the case with HMIs (or an entire LED light panel when its' emitters reach low light failure.) Where a 575w HMI globe typically retails for approximately $150.00, the 5000 hr L85 lamp life of an LEP bulb is equal to seven HMI globes, which amounts to a savings of $1050.00, or nearly half the cost of the Helio 270 Plasma lamp head.

 

Plasma_Helio270LG.jpg

The Helio 270 LEP

 

Another advantage is that Plasma emitters use solid state, hardened components that improve their reliability under harsh location production. Plasma bulbs are rugged and vibration resistant, and so will not break or explode inside expensive lighting heads the way HMI bulbs can. Since the LEP emitter is extremely compact, in the case of the Helio 270 at least the emitter, driver, and power supply all fit in the lamp head (the Photon Beard Nova 270 uses a separate AC power supply), eliminating the need for a separate ballast connected by header cables (the acknowledged Achilles heel of HMI systems.) Finally, with much lower UV emissions, LEPs do not require elaborate and ultimately finicky safety switches. In total, LEPs have an order of magnitude better reliability than conventional HMI lamp heads while offering the same intense beam and the colorful spectrum needed for motion picture production.

 

Finally, Power Factor Correction (PFC) is standard in LEP lamp heads where it is not in HMI ballasts. In fact there is one LEP head that we are looking at (not the Photon Beard Nova 270 – it’s too expensive) because it has a Power Factor of .99 making it a near linear load. As a result, it uses power more efficiently, minimizes return current, and generates virtually no line noise. Where, it is as much the Harmonic Noise that non-PFC HMI, Fluorescent, and LED power supplies kick back into the power stream, as it is their higher Apparent Power, that limits the total number of them that can be reliably operated on conventional portable generators; the efficiency and near unity Power Factor of this LEP head means that you can operate more of them on portable gas generators. For instance, you can only safely operate four 575W HMIs on a 6500W portable AVR generator, where you should be able to operate 23 of these 270W LEP heads (each with an output comparable to a 575W HMI).

 

Plasma_PowerWaveform.jpg

Oscilloscope shots comparing the current and voltage waveforms of the PFC Helio 270 with an equivalent wattage of non-PFC LEDs

 

Besides better color rendering, light quality, and lamp life, this different method of transforming electricity into light has other benefits as well. For more details about LEPs see our newsletter article at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20LEPs.

 

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

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Guy,

 

Thanks for this post! Some great info on Plasma lighting. Have you had a chance to check out Hive Lighting's ( www.hivelighting.com ) new lamp heads. Hive debuted part of its product line at CineGear 2011 in LA. Here is the info on Hive's fresnel head the HORNET 180 http://www.hivelighting.com/PDFs/Hornet180Fresnel.pdf. A pretty different form factor than either the Helio or Photon Beard's Nova, the hexagon shaped housing is designed to link together. Also Hive has a spacelight model which may be of interest to you as well, the BUMBLEBEE 540 http://hivelighting.com/PDFs/BumbleBee540Spacelight.pdf uses 3 emitters and gives the equivalent output of a 6,000W tungsten spacelight.

 

There is a write up on Hive Lightings booth here: http://provideocoalition.com/index.php/Awilt/story/cine_gear_expo_la_2011/ as well as SeaChangers theatrical lamp and Multiquips fuel cell light tower.

 

I agree with you on the potential for Plasma and on the overblown lamp life that is being promoted by the bulb manufacturers. I recommend no more than a 10,000 hour bulb life expectation since the .08 degree color shift over those 10,000 hours will take the bulb from the 5300K to 6100K which keeps it in the usable daylight range during that period for film and television production. But at the 20,000 or 30,000 range the loss of output and color shift just aren't practical.

 

 

Jon Edward Miller

Director of Photography

www.jonedwardmiller.com

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Thanks, Guy. This is a wealth of information.

 

Please don't toss those used LEP's when they get to 5000 or 10,000 hours. I'd like to get some to play with. ;-)

 

Maybe it could work like used Nagra batteries in the old days. Sound guys used to pass them out for flashlight use.

 

 

 

 

 

-- J.S.

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Also Hive has a spacelight model which may be of interest to you as well, the BUMBLEBEE 540 http://hivelighting.com/PDFs/BumbleBee540Spacelight.pdf uses 3 emitters and gives the equivalent output of a 6,000W tungsten spacelight.

 

 

what's on top of the bumblebee? it looks like a ballast. The fixture looks heavy. One thing about old school space lights is that they're relative light, which makes it easier when rigging

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Once you cut through the hype, the bottom line is that LEP heads offer a number of advantages over LED & HMI technology. Where we are a long way off from having a single-die LED with sufficient output and correlated color temperature to match daylight, LEP lamps are really the only cost effective alternative to expensive HMI Fresnel systems when it comes to generating full spectrum daylight balanced light. This feature of LEPs benefits Red users and DSLR users in particular.

 

One downside to lighting for the 5000K native color balance of CMOS sensors in the past has been that it requires an all 5000K balanced lighting package and HMIs are considerably more expensive to buy or rent than other light sources. Kino Flo fixtures, particularly the Parabeams, are a cost effective alternative to HMIs because they can use either 3200K or 5500K tubes. But, the drawback to fluorescent fixtures (like LED fixtures) is that they generally have a very broad soft light output that drops off rapidly which means the units need to be positioned close to the subject they are lighting. This characteristic has always made them better suited to lighting documentary interviews than dramatic scenes.

 

With a 5300K output comparable to that of a 575 HMI Fresnel, the Helio 270 Plasma lamp in particular offers the same benefit of being a less expensive alternative to HMIs, but also offers the added benefit of being more versatile than a Kino Flo or LED light panel. Not only does it offer the capacity of traditional Tungsten/HMI Fresnels to throw and control its light output (making it a more suitable Key and Backlight source for lighting dramatic scenes), but it also has sufficient output to bounce it or waste some output to diffusion material to make it softer (existing LEDs put out barely enough, with none to waste.) It’s capacity to provide both hard crisp light that will throw a distance and is easily controlled, as well as offer soft light with diffusion, makes the Helio 270 much more versatile than any Fluorescent light or LED array presently available. It also offers a number of benefits that the new LED Fresnels and traditional HMI Fresnel do not.

 

For instance, LEPs do not require the active microprocessor color control that is required to assure consistent color rendition in the best LEDs on the market today. Absent such microprocessor based color management systems, LEPs are less expensive and more robust than LEDs. Plasma lamps also have a much more continuous color spectrum than even the best LED luminaries. As is evident in the Spectral Power Distribution graphs below, LEP lamps, unlike LED lamps, generate light at wavelengths shorter than 425nm - which means that violet colors will render better.

 

Plasma_vs_Mole_LED.jpg

 

And, unlike LED lamps, LEP lamps also output in the medium blue-cyan-turquoise range from about 465-510nm so aqua-type colors render well by comparison. Skin tones and warm, amber-yellow colors stand out better under LEP lamps because of the strong presence of their complementary colors. And, since the output of LEP lamps extend all the way out on the long-wavelength end (well beyond the 600 nm cutoff of LEDs), pinks, reds, oranges, and other long wave-length colors look vibrant under LEP light where they tend to look a little dull under LEDs. As a continuous spectrum source, colors not only appear more natural and vibrant under LEP lamps than under LED lamps, they also reproduce more accurately on the screen since, as is also evident by their spectral distribution graph, the output of LEP lamps is almost an exact match to the spectral sensitivity of daylight film emulsions and digital sensors. An added benefit to LEPs is that color meters, like the Minolta III F, that make their calculations of the Color Temperature (CT) based on a light sources continuous spectrum, are able to generate accurate reading of the CT and Green/Magenta of LEP lamps. Color meters are completely useless reading the “spiky” discontinuous color spectrum of LEDs (see my newsletter article for details .)

 

The biggest benefit to LEPs in comparison to HMIs has got to be the cost savings in not having to replace lamps every 500 - 750 hrs as is the case with HMIs (or an entire LED light panel when its' emitters reach low light failure.) Where a 575w HMI globe typically retails for approximately $150.00, the 5000 hr L85 lamp life of an LEP bulb is equal to seven HMI globes, which amounts to a savings of $1050.00, or nearly half the cost of the Helio 270 Plasma lamp head.

 

Plasma_Helio270LG.jpg

The Helio 270 LEP

 

Another advantage is that Plasma emitters use solid state, hardened components that improve their reliability under harsh location production. Plasma bulbs are rugged and vibration resistant, and so will not break or explode inside expensive lighting heads the way HMI bulbs can. Since the LEP emitter is extremely compact, in the case of the Helio 270 at least the emitter, driver, and power supply all fit in the lamp head (the Photon Beard Nova 270 uses a separate AC power supply), eliminating the need for a separate ballast connected by header cables (the acknowledged Achilles heel of HMI systems.) Finally, with much lower UV emissions, LEPs do not require elaborate and ultimately finicky safety switches. In total, LEPs have an order of magnitude better reliability than conventional HMI lamp heads while offering the same intense beam and the colorful spectrum needed for motion picture production.

 

Finally, Power Factor Correction (PFC) is standard in LEP lamp heads where it is not in HMI ballasts. In fact there is one LEP head that we are looking at (not the Photon Beard Nova 270 – it’s too expensive) because it has a Power Factor of .99 making it a near linear load. As a result, it uses power more efficiently, minimizes return current, and generates virtually no line noise. Where, it is as much the Harmonic Noise that non-PFC HMI, Fluorescent, and LED power supplies kick back into the power stream, as it is their higher Apparent Power, that limits the total number of them that can be reliably operated on conventional portable generators; the efficiency and near unity Power Factor of this LEP head means that you can operate more of them on portable gas generators. For instance, you can only safely operate four 575W HMIs on a 6500W portable AVR generator, where you should be able to operate 23 of these 270W LEP heads (each with an output comparable to a 575W HMI).

 

Plasma_PowerWaveform.jpg

Oscilloscope shots comparing the current and voltage waveforms of the PFC Helio 270 with an equivalent wattage of non-PFC LEDs

 

Besides better color rendering, light quality, and lamp life, this different method of transforming electricity into light has other benefits as well. For more details about LEPs see our newsletter article at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20LEPs.

 

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

 

 

i hear they take ages to restrike after you pulled the power?

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For the record, Jon is co-creator and owner of Hive Lighting.

 

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

 

 

Guy,

 

Absolutely true, I am co-founder and creator of Hive Lighting. Sorry if there was any confusion, certainly wasn't trying to "pull a fast one". I assumed since my name is all over our website and I signed the post that was pretty clear but I apologize if that wasn't up front. In fact here is a video of me explaining more about Hive and Plasma lighting: http://wideopencamera.com/cine-gear-...hive-lighting/ so you can all put a face to my name.

 

I started Hive because of the potential I think plasma has for film and television, so I am excited to see the conversation on these forums as the word gets out.

.

 

Cheers,

 

Jon Edward Miller

Director of Photography

www.jonedwardmiller.com

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what's on top of the bumblebee? it looks like a ballast. The fixture looks heavy. One thing about old school space lights is that they're relative light, which makes it easier when rigging

 

 

Freddie,

 

Great point! Yes a plasma spacelight is going to be heavier than a 6K tungsten, no question, there are RFdrivers (solid state electronics) and heat sinks (silent thermal transfer) aka lots more metal then your traditional spacelight, so more weight. In fact our Bumblebee comes in around 35 pounds. Having said that where you do save is the weight of rigging very heavy socapex, banded bates or 4awg cable to bring up 6,000watts of power to each light. With an 825 watt system the amount of cable is significantly less, at roughly 7lbs per foot of 4 Awg the weight of the reduced copper alone offsets the weight difference very quickly. Also with the long bulb life compared to 6 1K tungsten globes you are saving a lot of hassle from constantly replacing bulbs. But with any new technology there are tradeoffs, we still believe the benefits of plasma greatly outweigh (excuse the pun) any downside.

 

Cheers,

 

Jon

 

PS in case there is any confusion I want to repeat I am the co-founder of Hive Lighting which uses plasma emitters in our lamps, so I obviously believe in the technology, having said I aim to educate and answer questions honestly, also if you have any problem with any of our products, please dont' hesitate to tell us what went wrong or what we can improve.

 

Jon Edward Miller

Director of Photography

www.jonedwardmiller.com

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i hear they take ages to restrike after you pulled the power?

 

Freddie,

 

Another good point. While Plasma is hot restrike, you don't need to wait after unplugging for the system to cool to plug right back in, but they are not instant restrike. Plasma emitters will take up to 2 minutes to hot restrike, and average 80 seconds. Certainly this is not ideal, and as a cinematographer I understand the stress that can come from somebody kicking our your power chord and then having to wait 2 minutes that may feel like an eternity for the light to turn on while the cast and crew stare at you. Having said that, compared to the time required to replace a bulb in an HMI when it pops or find and switch a breaker when the high wattage of a tungsten overdraws a circuit etc or the dozen or so other ways in which our lights can fail us on a set, I would consider it manageable. Of course that is a matter of opinion and I like Plasma technology and also have started to develop a comfort level, with any new technology there are new challenges, its up to us as DPs, Gaffers, and electricians to decide what we can and can't live with. I can tell you that working on speeding up the restrike time is something that is going on with plasma manufacturers although there is no clear timeline that has been announced.

 

Cheers,

 

Jon Edward Miller

Director of Photography

www.jonedwardmiller.com

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Well, i think Plasma technology is definitely interesting and fascinating, i'm all up for a greener and more efficient technology, but realistically i can't see it taking over the current technology until the colour temp issues and re strike times are sorted.

 

Regarding the bumblebee, i was wondering how easy it is to store and transport it. say you've got to rig 150 of them in a studio, how easy it is to pack all of them? thats the beauty of space lights, theyre just so easy to move, rig etc.

 

p.s- socapex isnt heavy at all where im from! but maybe thats because we're on 240v here and our distro is much easier than yours?

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... i can't see it ( Plasma technology ) taking over the current technology until the colour temp issues and re strike times are sorted.

 

While the restrike times on Plasma lamps is not ideal, they are, in my experience, no different than HMIs. I have never encountered an HMI that was consistently restrikeable. For that reason I always avoid turning them off unless I know there will be several minutes before they will be needed again and I always run out a second head cable if there is any question about the head placement so that it can move without being turned off. Taking similar precautions with LEPs will assure that you are never left waiting for the light to restrike, unless of course there was an unexpected kick out.

 

Freddie, what do you see to be the "colour temp issues?" Please elaborate.

 

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

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p.s- socapex isnt heavy at all where im from! but maybe thats because we're on 240v here and our distro is much easier than yours?

 

 

Freddie,

 

The bumblebees are designed to stack, they can sit on top of each other or on the floor safely or in a truck or shelves. The idea was to make them easy to stack and transport on a cart or lift etc. The other ease of use I forgot to mention is they are designed to fit inside 2K bags even though they give 6K output, so they are much smaller in circumference then you're standard 6K spacelights.

 

Finally just cause I like to think we Californians can lift anything you boys from Oz can lift, for the record 100ft of socapex for one 6k mole space light weighs in at 60lbs (27.2 Kg) or almost 2 Hive Bumblebees. But in the spirit of Pacific friendship let's agree that both my Bumblebee and socapex are light weight!

 

 

Cheers,

 

Jon Edward Miller

Director of Photography

www.jonedwardmiller.com

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Freddie, what do you see to be the "colour temp issues?" Please elaborate.

 

 

 

I'm mainly talking about features, Guy, the scenario is a fast paced, demanding and difficult job. Since LEP fixtures have such a pure and particular CT i think it would be hard and confusing to mix them on the floor with lights we already have available. I can see them at the moment being probably a great solution for Second Units, SFX units, car trailers, car scenes or smaller jobs like interviews where maybe you can't get a big gen set or much power and you need a punchy fixture.

 

The point is that it's really too early to say. As i meantioned above i do think it's an interesting technology and im not against it by all means.

 

People will use it, test it and if it really does wonders then im sure it will take over the industry! i'll be glad to wave HMIs goodbye, can't stand ballasts, header cables and the annoying rest of it!

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Finally just cause I like to think we Californians can lift anything you boys from Oz can lift, for the record 100ft of socapex for one 6k mole space light weighs in at 60lbs (27.2 Kg) or almost 2 Hive Bumblebees. But in the spirit of Pacific friendship let's agree that both my Bumblebee and socapex are light weight!

 

 

 

Good stuff. Sorry to say i'm not Australian, just happen to be working down here this year. Im giving sunny England a break!

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I'm mainly talking about features… Since LEP fixtures have such a pure and particular CT i think it would be hard and confusing to mix them on the floor with lights we already have available.

 

If you compare the spectral power distribution graphs (below) of natural daylight and LEP lamps you see that, except for very brief drop outs at approximately 410 nm and again at 451 nm, the light output of LEP lamps is almost identical to natural daylight and so will in fact mix easily with other daylight sources like HMIs, Daylight Kinos, and natural daylight.

 

Plasma_vs_Mole_LED.jpg

 

And, as also can be seen in their spectral distribution graphs above, Plasma lamps have a much more continuous color spectrum than even the best LED luminaries on the market today.

 

It is LEDs that don’t mix well with other sources. LEDs are so deficit in certain parts of the color spectrum that by the time you come up with a color gel pack to match them to a continuous light source like a tungsten or HMI light, the LED panel would put out very little light with all the gels on it. 3200K Phosphor White LEDs, in particular, don’t mix well with Tungsten sources. As you can see from the spectral power distribution graphs below, the spectral distribution of even high CRI Phospher White LEDs, like the Litepanels and Mole, are very dissimilar to that of Tungsten sources.

 

LED_Comp_Sprectrum.jpg

 

A spectral power distribution graph of a lamp indicates how much energy is present in each part of the spectrum. In the case of the 3200K Phosphor White LED above, the phosphors added shape the spectral distribution by enhancing certain colors in the spectrum to simulate the spectral distribution of incandescent light. As a result, the spectral distribution of Phosphor White LEDs resembles a series of peaks and valleys with a big spike at about 465nm (the blue LED) and a broader bump between 500 and 700nm produced by the phosphors. Even though the spectral power distribution has these peaks and valleys, the human eye perceives the light as white light.

 

While the discontinuous spectral distribution of high CRI White Phosphor LEDS (far left) may appear white to the eye, and the color of objects illuminated by it appear natural to the eye, to film emulsions and digital imaging systems designed to reproduce accurate color under the continuous spectrum of Tungsten lamps, the color of the same objects will appear unnatural on screen as the illustrations below make clear. That is, the hue of an object being illuminated by this "apparent white light" can be drastically different than expected when it appears on the screen. For example, below is a "Macbeth chart" contrasting the resulting effect upon different color swatches of studio Tungsten light and a representative high CRI 3200K Phosphor White LED lighting instrument (that shall remain nameless.)

 

LED_Macbeth_Tungsten-WhPhos.jpg

Split Macbeth chart: each color patch shows the visible effects of studio tungsten light in the top half of the patch, and a representative Phosphor White LED lighting instrument in the bottom half.

 

A common test chart used for assessing color performance of motion picture imaging systems, the chart above would be more accurately called a "split Macbeth chart" because each color patch shows the visible effects of the two light sources – Tungsten in the top half of the patch, and the Phosphor White LED lighting instrument in the bottom half. Although your computer display is not likely to be a calibrated reference monitor, the wide variations in color patch hue caused by the discontinuous spectral distribution of the Phosphor White LED lighting instrument should be readily apparent.

 

What accounts for these results? First, as you can see from its' spectral power distribution above, Phosphor White LEDS, compared to the continuous light output of Tungsten lamps, have no output at wavelengths shorter than about 425nm, which means that violet colors don't render well. Second, there is minimal output in the medium blue-cyan-turquoise range from about 465-510nm, which is why the aqua-type colors don't render well either. Lacking these complementary colors within the spectrum, skin tones and warm, amber-yellow colors don't stand out. Third, with the long-wavelengths cutoff in the high-600 nm range, pinks, reds, oranges, and other long wave-length colors tend to look a little dull under Phosphor White LEDs, compared with how they look under the continuous spectrum light of Tungsten filaments which extend all the way out on the long-wavelength end. Finally, as you can see from the gray scale at the bottom, this particular Phosphor White LED Luminary has an overall magenta bias. While you can white balance out/time out this magenta bias in digital video cameras/digital film intermediate if the scene is uniformly lit with the same LEDs, the camera/timer is not able to replace the parts of the spectrum that are missing all together. And since gels only rebalance the spectral distribution of a light source by passing the wavelength of the color that they are, gels cannot correct for these deficiencies because there is not light of those wavelengths to pass in White Phosphor LEDs to begin with.

 

LED_Model_Comp.jpg

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

 

This inability of LEDs to render color is very visible in tests recently performed by The Academy of Motion Picture Arts and Sciences (AMPAS) as part of their “Solid State Lighting Project Technical Assessment.” (see http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20AC%20LEDs 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 White Phosphor 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. You can also see above that, absent cyan, the skin tones don’t stand out because that complementary color (cyan) within the spectrum is not present. Since the light doesn’t put out much cyan, the camera/film simply can’t record it. And, as Cinematographer Daryn Okada, ASC, discovered the hard way, color gel packs, camera white balance, or digital intermediate timing can’t bring it out if it isn’t there to begin with.

 

Like many of us, Daryn Okada uses LEDs as “touch up” lights to add a little something where key lights drop off. Needing to touch up a face on one talent mark, he once hid a small LED unit behind a chair, to add some glow to an actress’s face when she reached a mark where the keys had fallen off. “The manufacturer claimed the unit to be a ‘tungsten LED source,’” he recounts. “She stopped right in the doorway, where I had this LED, and looked fine. But when I got the dailies back, her face was totally magenta.” What’s worse, Okada says the image could not be repaired in post, because there wasn’t enough of the right color of light in the scanned negative for a color timer to bring out. This examples demonstrates that, the bottom line is that, by nature of their discontinuous spectral distribution, even high CRI White Phosphor LEDs won’t mix well with Tungsten sources. Mixed with the uniform continuous light source of a studio lit with tungsten fixtures, the color deficiencies of Phosphor White LEDs will be quite noticeable and unacceptable by comparison.

 

 

Plasma_vs_Mole_LED.jpg

 

LEP lamps, by comparison, generate light with a continuous color spectrum that is almost an exact match to Daylight (see graphs above.) For instance, LEP lamps, unlike LED lamps, generate light at wavelengths shorter than 425nm. Unlike LED lamps, LEP lamps also output in the medium blue-cyan-turquoise range from about 465-510nm. And, the output of LEP lamps stay strong all the way out on the long-wavelength end, well beyond the 600 nm cutoff where the output of LEDs start to drop off rapidly. Capable of a fuller spectrum colors look more vibrant under LEP light where they tend to look a little dull under LEDs. Plasma lights, as opposed to LEDs, deliver the same output as full-spectrum Daylight or HMI sources.

 

LED_Lumen-Color_Shift_A.jpg

 

Another reason to stay away from Phosphor White LEDs in mixed light situations is that, as illustrated above, their output depreciates overtime and their color shifts much faster than the manufacturers say. For a detailed analysis of the practical implications of the color output of HMI, LED, and LEP lamps see our newsletter at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh%20Output%20AC%20LEDs.

 

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

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