LED color temp, how exact to we need to be?

T

treynolds

Well-known member
Ok so i am looking at some new LED lighting for my studio space and a lot of the manufacturers direct from china label it as 5500k-6000k, or 3200-3600k. To me that seems like a big range but then again the color spectrum for LEDs is different than back when we were in the Halogen days.

Then I got a color temp checking app on my iPhone and tested one little LED battery powered panel i have. Its a CN-126 and it tested at around 6200K, granted I don't know how accurate the app could really be and I don't have the money for a light meter that could give me color temp.

So, how accurate are the temp ratings for these LED's and how accurate do i need to be for my lights? If I just use something between 5000k and 6000k and then white balance to that will i be alright trying to match them with say a Kino Diva with daylight bulbs? How much wiggle room do i have before one source looks too blue or orange?

Thanks for the help guys, I guess there is a good reason I hire a gaffer on bigger shoots!
 
In theory, if the only variation between a given LED unit and a legacy unit is color temperature, you could sort it out with via a sheet of color correction gel (1/8 or 1/4 CTB or CTO and possible plus- or minus-green). In reality, cheap LED's can have any number of spectral spikes and dips in their output which means that even if the color temperature is tamed, they may never deliver comparable results. Look for units rated above 90 CRI as a start.
 
The LEDs I'm looking at are in strips and I will be putting them together to act as rugged kinos more or less. So if i were to end up with, say 78 CRI chips on these LED strips, how hard of a time would i have matching them to other lights?

I guess my question really boils down to this:
how far off can two sources be while still appearing balanced on camera?
I mean I know i can't mix daylights with tungsten, but when I mix my daylight lights with my strobes (around 6500k) they work fine.
 
What's your budget and what do you want to light ?

I've been very happy with the color and light output from the F&V K4000 daylight 1x1 LED lights, but if you're willing to spend a lot more you can get lights with a higher CRI rating. ( the F&V K4000 lights are 5400 Kelvin with their "milk" diffuser and 5650 Kelvin without any diffuser, and have no magenta/green shift. CRI rating is supposed to be 85. I have no way of confirming this, but I am happy with the results I am getting. )

Thread on F&V K4000 Lights

...One thing to keep in mind is that there are a whole bunch of lower-cost CRI 95 LED units that are going to hit the market later this year. I just ordered one of these tiny little units to see what the color is like, and I expect to see 1x1 units selling by the Fall. ( I suspect the larger units are being held back to try and clear stock of the older lower CRI lights, as they will be hard to sell once the CRI 95 units are out. )

Aputure Amaran AL-H160 High CRI 95+ 160 Ultra LED : $60 with Battery Pack
 
Its lighting for a white cyc im building.
While the Aputure lights look great, they obviously aren't large enough scale for what i am doing.
I have a large soft bank already that i use with strobes (8ftx16ft) and i was planning to add some LEDs inside for hot lights. That way i already have plenty of diffusion
 
treynolds said:
how far off can two sources be while still appearing balanced on camera?
Click to expand...
Not as far off as they can be to look the same to your eyes.
If you're talking about adhesive LED ribbon, there is no telling for sure what you're getting if it's coming from china. I got one roll of 3528 warm white ribbon that looks completely different from some 5050 warm white ribbon I got. Really, not even remotely close despite the fact that they're both classified as "warm white." And while the 3528 stuff is overall pretty close to a real tungsten light, certain colors just don't look the same no matter what.
 
The specifications by and large, are meaningless. I'm a fan of imported Chinese products but there's no doubt that their measurements used for the specs are hopeless. The iPhone apps are also just guides and only seem to make sense when looking at sources with continuous output spectrums - so just misread on LED sources. Something that looks white might well be adjusted very oddly when doing a white balance, and realistically you need to use your eyes to balance up a cheap LED source. Second problem is that batches from only a few days apart may be using LEDs from a different source, so any proper measurements made are out of date so quickly. All you can do is have a go!
 
treynolds said:
While the Aputure lights look great, they obviously aren't large enough scale for what i am doing
Click to expand...

These tiny little Aputure lights are simply a taste of what's to come, as larger 90+ CRI 1x1 lights will be shipping later this year. I ordered one of these tiny lights just so I can test the color output, which will definitely influence my decision about buying the 1x1 models when they are finally here.
 
The strips i was looking at are both identical barring color temp. The warm white is rated at 2800-3300k and the cool white is 6000-6500k. I was going to buidl them out side by side each on a dimmer so i can do all warm, all cool, or dial in the color somewhere in between. I think that way i will be able to warm up the cool white enough or cool down to match whatever i might throw at it down below.
 
Leds may vary greatly in color temperature as specified , even for the same model unit. Unless the emitters are from the same binning and batch, they may be "off" by as much as 10% from their spec'd data sheets. Also to consider is that as they are dimmed, they also introduce a color shifting by as much as 5% from their native color rendition. High CRI numbers really are not a measure of light quality although the higher the better BUT the real test is visually once the light is on. I have used many leds from different manufacturers and have come to select a narrow few from just 3 led makers, and even from those, I try to order in batches of 500 emitters having the same die batch and binning number. CRI is the last thing I look for as consistency and quality control from batch to batch is more important. I made many prototypes using 80 CRI led emitters that showed far better color reproduction than some claimed 90+ CRI units.
Variable color control by adjusting the "mix" of cool and warm ratio is a common scheme but once the color is set at a certain temperature say 3870 K, dimming can only be obtained by maintaining the set ratio of both colors. Somewhat difficult without a dedicated led driver designed just for that purpose. I would recommend a very simple approach in that both sets of cool and warm leds are driven by just a single led driver that has an analog dimmer potentiometer which controls the driver's output current that feeds a 3 way on-on-on switch thereby having a choice of only 3 color temperatures. Cool, neutral and warm. No in-between choices. So if you use 5500K as cool and 3200K as warm leds, then you may get 5500- 4500 and 3200K set choices with full 0-100% dimming control. Warmer leds have less lumen output than their cooler counterparts. Not an issue but the camera aperture can easily adjust to that.
If you are planning to use leds in a 8X16 foot softbox, you will find out that you may need plenty of leds considering the diffusion loss as well as the emitter to diffuser internal distance. You may consider using instead power class leds like Cree's CXA or Bridgelux BRXA's series, and even with those you may well need 6 or more of them with dedicated electronics to drive them, not talking about proper heat management yet. 8X16' is mighty large. I don't think led strips will be up to the task.
 
my concern with the single sources like the BXRA LEDs is just the number of them and the placement. I figured it would be easier to soften up the smaller sources than it would fewer larger ones. Granted the prices for the BXRA's aren't bad, but at around 900Lm per unit i would need quite a few no? Or are you refereing to the larger 9000lm models?

How much light do you think I will need The strips i am looking at are about 1200Lm per meter. I am going to put at least 12 meters with in this bank giving me ~14400 lumens. I was thinking back to my halogens and a 1k fresnel was rated at about 1600lm @ 1m. Or am i way off base here? I don't want to come across sounding like i know better because obviously i don't know as much as a lot of people on here. Think i have enough light in there then? I could always add more strips, I just want to make sure i get enough the first round and don't try to mess with adding more from a different lot down the line.
 
You could take the easy (and cheap) way out and stick two quad biax flos behind your diffusion. That's a lot of light for under 500 watts power draw. Close to 2K worth of daylight, and the technology is mature and tested.
 
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