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Author Topic: Lighting for continuous color control for Still-life "theatre".  (Read 2497 times)
KirbyKrieger
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« on: March 14, 2013, 11:27:19 AM »
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Hi.  I'm looking to set up a relatively small (1m cube), inexpensive still-life "theatre" in which I can control the hues of several lights.  The hue control must be _continuously_ variable across the spectrum.  The ability to control the luminosity is desired, but not necessary.  Brightness is not required (I will increase the exposure duration as needed), but would also be useful.  "Expensive" would be more than a couple hundred dollars US.

As a proof of concept, I used an iPad running the app "SoftBox Pro" as a light source.  I liked what I was able to do.

I am considering the Philips product "Hue" (LED lightbulbs controlled by an iOS app), but am concerned about the usefulness of the controller app, which receives many negative reviews.

All information and recommendations welcome.  Thanks!
(I realize this isn't PP, but found no better sub-forum.)
(Also posted on Dyxum.)
« Last Edit: March 14, 2013, 11:31:51 AM by KirbyKrieger » Logged

Ernst Dinkla
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« Reply #1 on: March 15, 2013, 05:34:39 AM »
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With an ideal light source for slide duplication in mind (better than Illumitran) I have similar questions to answer.

Any LED solution right now will have spikes in the spectral distribution. Whether based on RGB LEDS or white shifting fluorescents on UV LEDS. The continuous spectral distribution white LEDs filtered by the smallest Quantum Dots possible are not marketed yet. Their Kelvin grade can vary depending on some tweaks and voltage difference. Right now low voltage halogens from 2800K to 5000K are the only option for continuous spectral output and different color temperatures.

Building something like Philips did but better will take time. You could at least check the spectral output of the RGB LEDs and whether they fit the camera sensor sensitivity best, of both data is on the web. There will be an electronic scheme somewhere on the web too, tinkerers like to replicate what is on the market. In the disco scene there will be amateur up to pro equipment like that.

Another somewhat rougher approach is your iPADdisplay trick translated to two small secondhand flatscreens, a PC and two videocards. Color per screen and gradations per screen etc. possible. Someone must have done that before and open source software could be available. Spikes are still there from the LCDs backlight.

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Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.
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KirbyKrieger
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« Reply #2 on: March 15, 2013, 09:38:06 PM »
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Ernst -- thanks for the info.  I hadn't thought I was on the bleeding edge.  O well -- will stumble in a direction that, if I land on my feet, I will call "forward".

--Kirby.
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Ernst Dinkla
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« Reply #3 on: March 16, 2013, 05:50:56 AM »
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Bleeding edge is what you look for first. Budget, lateral thinking, tinkering and time will create the practical compromise.

Edit: or Google: http://www.youtube.com/watch?v=J3uACCayLHg


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Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.
« Last Edit: March 16, 2013, 10:56:55 AM by Ernst Dinkla » Logged
MarkM
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« Reply #4 on: March 16, 2013, 12:44:16 PM »
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I have a bunch of the Philips Hue bulbs and have experimented with them quite a bit. They're a little expensive if you are unsure whether they will work. Here's a few things that might help:

The iOS app is great for the day-to-day use Philips imagined the bulbs would see. It's easy and fast. But you can't be very precise. For instance you can't pick colors by number or CCT.  The system does have a very elegant API that you can access quite easily through the browser or a terminal app. A little googling will get you the info you need. Basically you can use it to control everything in a quick, programmable, and repeatable way. The API allows you to specify color as xy chromaticity, correlated color temperature, etc. And since it's a REST API, you don't need to write a bunch of code—just craft a URL with the parameters you want.

I wouldn't describe the spectrum as spiky. It's more "'hilly'. Philips is doing something with phosphors to spread out the bandwidth of the light, especially from the green LED. I suspect this is how they're achieving good whites and the relatively high CRI. The spectrum does have some deep dips. Whether that matters will depend on the nature of what you're shooting. It can't be worse than light from the iPad.
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Ernst Dinkla
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« Reply #5 on: March 16, 2013, 02:28:14 PM »
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Mark,

Any webpage where I can see the spectral plot of the Philips Hue bulb?

Disco type RGB LED controllers, some up to 16.7 M color, in Dutch though:
http://www.conrad.nl/ce/nl/search/?search=LED-strip-regeleenheid

--
Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.
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MarkM
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« Reply #6 on: March 16, 2013, 02:51:37 PM »
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Mark,

Any webpage where I can see the spectral plot of the Philips Hue bulb?


I haven't seen plots published on the web. I've attached a plot of the spectral power I made myself with an I1 Pro. It was fairly quick and dirty, so it might have a little pollution from other light sources, but not much. This is several plots on top of each other as the lights go from CCT 2000K to 6500K in steps of 500k.
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Ernst Dinkla
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« Reply #7 on: March 17, 2013, 07:17:34 AM »
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I haven't seen plots published on the web. I've attached a plot of the spectral power I made myself with an I1 Pro. It was fairly quick and dirty, so it might have a little pollution from other light sources, but not much. This is several plots on top of each other as the lights go from CCT 2000K to 6500K in steps of 500k.

The spectral output fits the spectral sensitivity of my 5D MK II but on the RED, the Philips Hue LED goes to longer wavelengths there. You are right about the flattened green output.

The LED strips for the Conrad controller have their output at RGB 620-630Nm, 520-530Nm, 470-480Nm.


--
Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.
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KirbyKrieger
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« Reply #8 on: March 20, 2013, 03:02:36 PM »
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I haven't seen plots published on the web. I've attached a plot of the spectral power I made myself with an I1 Pro. It was fairly quick and dirty, so it might have a little pollution from other light sources, but not much. This is several plots on top of each other as the lights go from CCT 2000K to 6500K in steps of 500k.
I would like to make spectral plots of the Hue® lamp with and without the glass bulb.  I have -- inadvertently  Cry -- removed the glass bulb from one lamp.  There are eleven LEDs:  5 yellow (to the naked eye, off), 4 red, 3 "white".  When on, these emit what appears to be green, red, and blue light (reflected off a white surface).

Can I do usable rough measurement with an X-Rite Color Munki?  It does NOT profile projectors.

Thanks.
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Ernst Dinkla
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« Reply #9 on: March 21, 2013, 04:13:05 AM »
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I would like to make spectral plots of the Hue® lamp with and without the glass bulb.  I have -- inadvertently  Cry -- removed the glass bulb from one lamp.  There are eleven LEDs:  5 yellow (to the naked eye, off), 4 red, 3 "white".  When on, these emit what appears to be green, red, and blue light (reflected off a white surface).

Can I do usable rough measurement with an X-Rite Color Munki?  It does NOT profile projectors.

Thanks.

The Color Munki actually does not measure a wide spectral range in reflective mode, only 430-730 NM, but might measure wide enough in the monitor mode. You would need a spectral range output in numbers. If that does not exist in X-rite or GM software tools then ArgyllCMS will have something to use.
Put the Color Munki far enough from the lamp to get correct readings. Fix both that the angles of light reception do not change. It is wise to put one layer of plumber's teflon tape over the Munki's sensor entrance. Neutral enough to keep the result sensible. Monitor mode, or ambient light if the Munki supports that.

My 2 cents.

--
Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.

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KirbyKrieger
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« Reply #10 on: March 21, 2013, 08:18:39 AM »
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Ernst -- Thanks for the knowledgeable and helpful reply.  I'll give it a try.

--Kirby.
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