Are there any tungsten LED's that actually look good?

[Matt Irwin]

Hi,

 

I was just curious if anyone has run into tungsten balanced LED sources that actually mix seamlessly with normal tungsten and 3200 kino tubes.

I've run into a variety of options- Litepanels, lowel, most recently LiteRibbon- and while LiteRibbon looked really nice with some 1/4 MG, they all look like garbage when compared to honest tungsten. LED tech improves 200% every 18 months, so just curious if there are any latest/greatest tools out there.

 

I understand that the B&M's MacTech tubes are near perfect, and those new Mole sources are the same... but I'm looking for something very compact, hideable, and battery powered.

 

Cheers,

[Guy Holt]

I was just curious if anyone has run into tungsten balanced LED sources that actually mix seamlessly with normal tungsten and 3200 kino tubes…. they all look like garbage when compared to honest tungsten…. I understand that the B&M's MacTech tubes are near perfect, and those new Mole sources are the same....

 

Art Adams posted on CML recently a link to tests he shot comparing a wide range of LED fixtures for their color rendition. Apparently there is some question about the validity of his methodology on those boards, but the tests are informative all the same, so you might want to look at them before making statements like “I understand that the B&M's MacTech tubes are near perfect, and those new Mole sources are the same.”

 

LED tech improves 200% every 18 months, so just curious if there are any latest/greatest tools out there.

 

David Pringle, the founder/owner of Lightning Strikes/Luminys/Softsun, correctly questioned in the same CML thread that, where that might be the case, will manufacturers of LEDs necessarily trade off better color output for diminished efficiency and lumen output?

 

Almost any LED can be sufficiently doped with enough phosphors (remote or not) of the right colors and quantities to achieve good color quality and high CRI. But the price of these extra phosphors is a decrease in luminous efficiency….. The point is there is a substantial penalty to pay in light output in order to get an LED to perform almost as good as tungsten. Is it worthwhile for other LED lights to follow the same course as the Foton to substantially improve the spectral output at the expense of light output, or is the savings in power with the convenience of simple house power wall plug or battery operation enough to justify the well known (and now well documented) sacrifice in color quality? in the spectrum.

 

Besides, the now well established deficiencies in the color output of LEDs, they also have the problem that, where 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.

 

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.)

 

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

[Torben Greve]

Keep an eye on NAB... according to AbelCine, the next step in LEDs will fix some problems that might make them more interesting. I for one have not discounted them, just like everything else, they need to evolve... Ofcourse they might get sidewinded by plasma lights, but lets see :)

[Phil Rhodes]

I'm at NAB and I'll keep an eye on this, as it's been a concern of mine for a while.If there's anything in particular you want looked at, let me know.

[Guy Holt]

... according to AbelCine, the next step in LEDs will fix some problems that might make them more interesting.

 

If it was Mitch Gross at Abelcine that said this, he was probably referring to the PRG Foton (he has been promoting it heavily.) It was in fact the Foton that David Pringle was referring to above. He also correctly observed about the Foton:

 

… it should be pointed out that these units (the PRG Foton) have paid a price for this color improvement. Almost any LED can be sufficiently doped with enough phosphors (remote or not) of the right colors and quantities to achieve good color quality and high CRI. But the price of these extra phosphors is a decrease in luminous efficiency. Note that as stated in a previous post the TruColor Foton produces only 50 lumens per watt. When you consider that Tungsten produces 28-30 lumens per watt, you are not getting much more light from the Foton in spite of a much higher price. For the difference in light output, why not just stick with a Tungsten light and not have to worry about unpredictable spikes and valleys in the spectrum.

 

 

Guy Holt, Gaffer, ScreenLight & Grip

[Torben Greve]

Good point... it just bothers me there's no middle ground :D I'm so spoiled I want the best of both worlds: low wattage + full spectrum white + nice throw and quality of tonage = win. Hehe... I know this is unrealistic for now, but man...

 

I guess one could just choose to look past the spike issues. I know the Danish tv stations don't give a rat's. The amongst other lamps use TecPro.

[Guy Holt]

Good point... it just bothers me there's no middle ground :D I'm so spoiled I want the best of both worlds: low wattage + full spectrum white + nice throw and quality of tonage = win. Hehe... I know this is unrealistic for now, but man...

 

This is exactly how PRG is marketing their Foton. In my opinion the Foton still suffers the inherent limitations of all LEDs (Remote or not) using Phosphor Technology to generate colors with longer wavelengths. 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.)

 

If you compare the Spectral Power Distribution Graph for the Foton to that of a true black body radiator like a Tungsten filament, the Foton clearly suffers from these limitations. Compared to a black body radiator source like a Tungsten filament, the output of the Foton drops off steeply below its pump color (which is at 425nm 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 Foton appears to generate more light in the medium blue-cyan-turquoise range from about 465-510nm than the typical Phosphor White LED, 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 will look dull under the Foton, compared with how they look under a Tungsten source which continues strong all the way out on the long-wavelength end.

 

Marginally better than the typical Phosphor White LED, I would not say it “correlates perfectly with professional light” and surely does not “eliminate the challenge of lighting with (the) discontinuous spectrum inherent in most LED lighting sources” as PRG claims on their website.

 

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