Spectral Emmision Curves - LED/Flo

[Michael Pugliese]

So this has been on my mind recently with the new LED production lights Arri just put out. It seems extremely misleading that not a single one of these manufacturers publishes the emission curves for these units. Not Nila, LEDZ, Arri, or even CoolLights (who give emission data for their fluorescents!) I have a deep seeded feeling that the lack of information is due to an embarrassingly messy curve. This feeling is reinforced by researching spec sheets from the top LED manufacturers.

Everyone falls back on providing meaningless CRI numbers that really don't give any idea of the actual quality of the light. There seems to be a big myth in the industry that CRI is a barometer of color quality. Nothing could be more untrue. I was taught this too in my early cinematography class', and definitely learned my lesson the first time I noticed Wal-Mart sold florescent "Plant & Aquarium" bulbs with a CRI of 91. Holy Shit! Turns out when I tested the bulbs with a spectrometer they were completely whack, and completely usable for anything besides lighting my non-existent aquarium. There is a way bigger difference between those and Kino bulbs than the extra 4 point of CRI. It's illustrated by looking at Kino's curves for their bulbs, which are startlingly good.

I see their use on big productions by big DPs, so I MUST be missing something, right? The only way we are able to emulate the spectral emission of a black body radiator in a fluorescent is the addition of reactive phosphors inside the tube, and this can't be done with a diode, right? Is Arri able to overcome color problems by mixing three dies? Has anyone tested these lights with a spectrometer?

 

[Matt W.]

Wikipedia has a bit of information on this:

http://en.wikipedia.org/wiki/Light-emitting_diode#White_light

Apparently, phosphor-coated LEDs do exist and are superior in terms of CRI (which, yes, is a borderline meaningless term) to RGB arrays. Exactly what Arri (and others) are using is anyone's guess. Remember that kinoflos are nearly half as efficient as even traditional mid-80 CRI tri-phosphor fluorescent lights so there's always a trade-off between efficiency and color rendering.

I've never been able to afford LED lighting so I've never worried about it, but I assume most DPs use LEDs only for special purposes or maybe they use LEDs exclusively and time out green spikes, etc.

 

[Guy Bryan Holt]

Remember that kinoflos are nearly half as efficient as even traditional mid-80 CRI tri-phosphor fluorescent lights so there's always a trade-off between efficiency and color rendering.

I've never been able to afford LED lighting so I've never worried about it, but I assume most DPs use LEDs only for special purposes or maybe they use LEDs exclusively and time out green spikes, etc.

All Kino Flo fixtures are not the same when it comes to efficiency, so you have to be careful when comparing them to LED lights. Unlike Kino Flo fixtures that use the T12 tubes, the Parabeam fixtures have Power Factor Correction circuitry built in that improves their power factor rating to over .9. This makes them an especially efficient fluorescent light source that is comparable to the power efficiency of LED light panels and suitable for battery operation. For instance a Parabeam 400 puts out more light than even Zylight’s new high output LED light panel yet draws just .2 Amps more power.

Like every other DP & Gaffer, I have put together my favorite lighting package based upon my more than 20 years operating a lighting rental and production service company. For my package, I have picked lights that I feel offer both the highest output (lumens/watt) and the best production capability and have combined them with distribution technology I've developed that enhances the production capability of the new Honda Inverter Generators. As yet, I have not found a LED lighting fixture that warrants inclusion in my package. Trust me, I have looked at all of them and some still to come. Here are a few of my reasons why I prefer the Parabeam 400 fixtures over LED Panels and it has to do with more than just their spectral distribution.

In HD Digital Cinema, the quality of light is more critical than ever. In High Def every detail of “on-camera” talent is rendered clearly on the screen – even the imperfections. Where LED and traditional hard light sources can exaggerate textural details, it is my opinion that fluorescent soft light is better for lighting talent in High Def productions because it can subdue those same textures and render a more cosmetic appearance. Primarily for this reason, I prefer the Kino Flo Parabeam fixtures, over LED Panels and other light sources, to serve as a Key source. Here are a few other reasons as well.

What distinguishes the Parabeam fixtures from LED Panels and other fluorescent lights is their throw, power efficiency, and the innovative accessories Kino Flo makes available for the fixtures. Accessories include barndoors, a gel frame, a diffusion panel, and Honeycomb Louvers. These features enhance the production capabilities of the Parabeam fixtures and make them suitable to serve as a key, or even backlight, source where conventional fluorescent movie lights and LED light panels are not.

Both conventional fluorescent movie lights (Kino Flo’s included) and LED light panels have a very broad light output that is hard to control. These lights also tend to drop off rapidly which means that to serve as a Key source, the units need to be positioned close to the subject they are lighting. These characteristics make them best suited to serve as Key sources in documentary interview set ups where the Keys are typically positioned close to the interview subject. In that capacity conventional fluorescent lights and LED light panels (with heavy diffusion) can generate a wonderful soft light that wraps around the interview subject without wilting them. But, given these characteristics, conventional fluorescent movie lights and LED light panels have only limited applications as fill sources in dramatic set lighting.

The ParaBeam fixtures, on the other hand, have computer aided designed (CAD) parabolic reflectors that focus their light output where it is needed most for lighting dramatic scenes - at a medium distance – making them better suited as a Key source for HD Digital Cinema. If you compare the photometric tables of the Parabeam 400 and the Diva 400 (which uses the same four lamps), you will notice that at 16’ the Parabeam 400 puts out almost three times the light level (28FC) than the Diva 400 (10FC) even though they both use the same tubes. You can always diffuse a Parabeam to create a soft source, but nothing you do will make a Diva 400 or LED light panel punchier.

In fact, a Parabeam 400 generates as much light at 16’ as the 4’ 8-Tube Kino Flathead 80 fixture, yet uses less than a quarter of the power (2 Amps verses 9.2 Amps.) While the seven amp difference is not a major consideration when using house power, it can make a difference when your power is limited (coming from a portable generator) because you can use four Parabeam 400s for the same power as a 4’ – 8 Bank Kino Flathead 80. And unlike the ballasts of Kino Flo’s fixture that use the T12 tubes, the Parabeam ballasts also include filters to reduce the return of harmonic currents into the power stream and improve their power efficiency.

While the newest LED light panels (that use the higher output LEDs) approach the Parabeams in output, the Parabeam fixtures are more easily controlled – an essential requirement in a Key source. Parabeam fixtures are controlled by interchanging Kino Flos’ innovative Honeycomb Louvers. Louvers are available in 90, 60 and 45 degrees. Swapping louvers provides beam control similar to that of swapping lenses on an HMI Par. These features enhance the production capabilities of the Parabeam fixtures and make them suitable to serve as a Key or Backlight source where conventional fluorescent movie lights and LED light panels will spill all over the set.

Kino Flo Parabeam fixtures are ideal for filming with the Red One. Since the Red’s native color balance is 5000K, it looks best when the lighting package consists of 5500K sources. Kino Flo Parabeam fixtures are a cost effective alternative to HMIs because they can use 5500K tubes. They provide beam control similar to that of swapping lenses on an HMI by interchanging their honeycomb louvers. And, they are even more efficient sources than HMIs. When using 5500K tubes to light for the Red’s 5000K native color balance, you can warm the lights without losing output to CTO gels by simply mixing in 3200K tubes with the 5500k tubes. Given the light sensitivity of the Red Camera, the more focused light of the Parabeam 400s is all that is needed for a key light even at a distance.

The power that I save by using Parabeam 400s for key sources in my package, enables me to power more lights on the enhanced 7500W output of my modified Honda EU6500is generator. Using a 60A Full Power Transformer/Distro on my modified Honda EU6500is I am able to power a lighting package that consists of a 2.5kw, 1200, & 800 HMI Pars, a couple of Parabeam 400s and Parabeam 200s, and a Flat Head 80. Given the light sensitivity of the Red Camera this is all the light I need to light a large night exterior. (Use this link - http://www.screenlightandgrip.com/html/emailnewsletter_generators.html - for a detailed description of the benefits to using Kino Parabeam 400s on portable generators (the section on the Parabeams is about three quarters of the way through the article.)

Compared to LED fixtures, Kino Flo Parabeam fixtures are just as efficient but offer greater versatility. Able to interchange different color temperature tubes, and vary beam spread with their interchangeable honeycomb louvers, the Parabeam fixture can do what it takes four different LED Litepanel fixtures to accomplish – Spot and Flood in both 5500K and 3200K. Offering better light quality, output, beam control, and versatility, the Kino Flo ParaBeams make for a better key or back light for HD cinema production than just about any other light source. Not to mention that you can buy two Parabeam 400s for the asking price of a single LED light panel.

Guy Holt, Gaffer, ScreenLight & Grip , Boston

 

[Joe G.]

Thanks Guy. Very informative.