Good 3rd party LED reviews

[James B.]

Hi
Can anyone recommend a good objective comparison of the various LED options on the market, from low end to high end?

Listening to Gale Tattersall workshop over the weekend he mentioned Cinemills
http://cinemills.com/ledz/index.htm

but was wondering what other options there are in the market.

I'm primarily interested in a CRI comparison of the lights and how much better a LED costing $3000 is over one costing less than $100?

 

[Kwan Khan]

http://www.coollights.biz/fixture-s....html?osCsid=9aaae7805c31e7551e61e850dc573ef4

 

[Olivier Madar]

I recommend you the new Coollight PAR 1200 Led bicolor. Very light and powerfull. I always carry 2 of them with me. Richard, please, can you make us an external battery solution for powering them ?



Olivier

 

[Kwan Khan]

Richard, please, can you make us an external battery solution for powering them ?

Olivier

+1 vote

 

[Martin Weiss]

Looks like Richard has heard you even before you asked

External battery interface will be accomplished with the forthcoming LED 1200 battery interface option.

 

[Richard Andrewski]

I recommend you the new Coollight PAR 1200 Led bicolor. Very light and powerfull. I always carry 2 of them with me. Richard, please, can you make us an external battery solution for powering them ?
Olivier

Thanks for the mention Olivier and everyone! Been so busy this summer I haven't had a chance to check in much. We are working on the battery interface, its in testing now, will go into production very soon. I'll have pricing and pictures soon as well. Working on many other interesting things as well which are in testing now ;-).

 

[Eric Jaspers]

Hi
Can anyone recommend a good objective comparison of the various LED options on the market, from low end to high end?

I'm primarily interested in a CRI comparison of the lights and how much better a LED costing $3000 is over one costing less than $100?

It has been well established elsewhere in this forum that CRI is not necessarily the best indicator to judge the color rendering capability of LED fixtures because it is a measurement that can be manipulated by manufacturers to give high readings without giving good results. For a more accurate assessment of the color rendering capability of LED fixtures you have to look at the spectral power distribution of the fixture as the Academy of Motion Picture Arts and Sciences (AMPAS) did as part of their “Solid State Lighting Project Technical Assessment.” For a good objective 3rd party analysis of AMPAS’ comparison of LED fixtures I would suggest the followng article on LEDS.

To summarize this article: when it comes to LED lights, you get what you pay for. The reason Litepanels are more expensive than Cool Lights is that they are a better made light. For instance the linear voltage regulator that Cool Lights uses in their heads to stabilize the LED current has several drawbacks in comparison to the approach that Litepanels uses which is a DC-to-DC switched-mode power supply (SMPS) in conjunction with a constant current regulator in the light head. The first drawback to Cool Light’s approach is that considerable energy is wasted in the series resistors. Second, the linear voltage regulator that converts the supply voltage to the desired voltage for the LED strings maintains a constant output by wasting excess electrical energy by converting it to heat. As such, this approach is highly inefficient and not ideal for battery operation. The same function is performed more efficiently by using a DC-to-DC switched-mode power
supply (SMPS) in conjunction with a constant current regulator in the light head.

Another big difference is in the color output of the LEDs used in the two heads. Litepanels uses much more stringent parameters in the binning process so the color output of their heads is more accurate and consistent between heads. But, even with more stringent binning the approach that both Litepanels and Cool Lights take to generating white light with LEDs – Phosphor White Technology - has an inherent limitation: by their nature the spectral distribution of Phosphor White LEDs is less than optimum for motion picture lighting applications (use this link for details.)

While they are less than perfect at reproducing parts of the color spectrum, the color rendering of Phosphor White LEDs may be adequate in certain situations. For a specific application, say where lights must be operated off of batteries, a LED fixture offers the unique advantage of greater power efficiency over conventional lights, which may out weigh its shortcomings in color rendering. However, a Phosphor White LED is clearly not the best choice in applications where color rendition is critical (food/product shots) or mixed with a uniform continuous light source, such as a studio lit with tungsten fixtures, where its color deficiencies will be quite noticeable and unacceptable in comparison (see this thread for more details.

- Eric Jaspers

 

[Rob Ruffo]

Uh... You just add some minus green and no real problems. As far as power draw, the CoolLight LED panels take almost none at all, so if another panel would save me 3c per year of electricity and costs $ 1000 more then that's maybe that's not good value for that difference. The thing is, can we see a difference? I say no (if you use the right minus green recipe which isn't terribly hard to figure out) I can see none on shots done with Litepanels vs. CoolLights. That said, LED is its own look, not the same as other light types and in no way a replacement for them.

 

[Eric Jaspers]

Uh... You just add some minus green and no real problems .

The problem with correcting Cool Lights LEDs with gels is that you have to constantly adjust your green/magenta correction depending on the temperature at which the LEDs are operating. That is because a one degree shift in the junction temperature of the blue InGaN LED (pump color) in remote phosphor LEDs, will cause a +/- 2nm shift in the dominant wavelength. If compounded by the average wavelength variation of +/- 2nm of blue InGaN LEDs, a 5nm divergence from the prescribed 455nm wavelength of the pump color will create color inconsistency of 5 MacAdams ellispses. While not readily apparent to the eye, image capture systems will easily see this variation resulting from a change in ambient temperature.

The problem is that high power Phosphor White LEDs like those used in Cool Lights and Litepanels require a high degree of power conditioning when used on AC power because the current drawn by LEDs is an exponential function of voltage. That is a small voltage change results in a large change in current and temperature. It is therefore critically important that the right DC voltage be provided to the diodes. If the voltage is below the threshold, or on-voltage, no current will flow and the result is an unlit LED. If the voltage is too high, the current will go above the maximum rating and begin to heat the LED. To make matters worse, as an LED warms up, its voltage drop decreases, further increasing current.

Basically technology from the 50s, the linear voltage regulator used in Cool Lights LEDs are simply not as good at maintaining the prescribed voltage and temperature at the LED diodes as the approach Litepanels uses, so there is a wider variance in color over time. Trying to correct the color shift in Cool Lights LEDs is like trying to hit a constantly moving target. Litepanels, by comparison, uses an up-to-date DC-to-DC switched-mode power supply (SMPS) in conjunction with a constant current regulator in the light head. This approach is not only more efficient, but also much better at maintaining a constant current and temperature at the LED diode so there is less color variation. For more detailed information about the differences in LED fixtures, I would suggest this article on LEDS.

- Eric Jaspers