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Looking for RGB or RGBW values of a sunrise
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Twoflower:
About the 'Sun colour' and the 'sky colour'. That's a question I had also in my mind and feared to answer. To be honest I can't give an answer here. Probably a mixture from both. As my project is actually a try to get me awake in the winter time this is probably a question I should ask in a medic-forum. The only paper I'm aware of is that the blue light seems to be problematic if you want to sleep. So probably it's a good idea to have the blue hour in the show included. I'm sure there are papers out there but I haven't looked. But as the lookup table isn't set in stone OTP-ROM. I can run some tries to see how it will eventually turn out.

Using the the RGBW sensor/Camera/Simulation I can probably tweak the opening of the viewing angle to change the ratio between full sky (180°) and more sun-whigted configuration (e.g. 20°).

@BrianHG: That sounds interesting. Maybe I'll come back later to your offer. The RGBW sensor looks very tempting and adds to my current project another one. Plus an easy way to run a room calibration.

@cdev: That dichroic filters would require a full spectrum light-source. I'm not sure is a white LED will working well enough. And would eat a lot of the light as the not used light will be reflected the other direction. The plan is to flood a roof-wall (45° angle). I'm not sure if such filters exist for a line shaped light source and probably would require motors/servos to change the colour. I've seen lamps having such filters, they look very interesting.

So probably the plug in is not available. Might have been interesting of the results.

@rs20: I started my idea with the cam approach. But it has some downsides as well.

One of the problems of a cam might be the dynamic range of a prosumer/consumer cam (like the EOS D5 Mk3 that is floating around here). Starting a the blue hour running until the sun is reasonable above the horizon is probably too much. So you need to take care there too. Not impossible but something you need to take care of.

The colour sensor would be fitted with a opaque dome. I never came to the idea to use the bare sensor. This could also reduce the environmental impact. Just limit the viewing angle to the upper part of the sky.

the demo you mentioned sounds nice. I would like to have seen it. Yes the human eye-brain combo is fascinating. The dynamic range of the eye on one side and how easy the brain can be fooled on the other side.

Thanks for the heads up with the non linearity of the standard colour system. One more reason to use the RGB sensor. You can keep the whole flow relatively controlled. The only pitfall here I see is the room-calibration. In case the LED colours don't match reasonable with the filters of the sensor. That would probably need a fall back to the white sensor channel and run the calibration for each colour channel  independent. But that probably counts also if I would use a camera for this calibration run, but with no fall-back solution.

Again thank you very much for this productive discussion.
cdev:
Blue LED light all by itself should be diffused by bouncing it off of something - Blue LEDs shining at you above a certain level thats not as high as we would wish may damage the eyes.

I found lots of stuff about this on pubmed.

Interesting, other colors may have other effects.. Red light, as I am sure you know, is postulated to be better for people before they go to sleep.. I even found some tantalizing side excursions that I bookmarked but have not had the time to explore more fully..

Green light may be good for your health :) 

Its my understanding that the pineal gland is where our body's circadian rhythm is regulated.

cdev:
I thought you were undertaking some kind of artistic project or installation.

There is a lot of variation in sunrises and sunsets both seasonally and geographically.

If you can get a decent camera, whose color rendition you trust, you could maybe mount it in a fixed position and use it to take standardized photographs at fixed intervals. Maybe once each minute at exactly the minute. Store them in a database and then you could call it up, you could also create custom functions so you could say, get a animation which represented the same time before or after the sunrise and or sunset throughout the year. You should also bracket extensively so you can do HDR. You likely could keep a single camera very busy all the time.

That would tell you more about the colors and trends than anything else I could think of, perhaps.

You might want to take a look at the biological pathways involved in the circadian rhythm system.

I have two friends who have studied the process of wakefulness and sleep - extensively. Haven't talked to one in decades and the other is now deceased..

But its very interesting stuff.

Issues like SAD may be rooted in some amino acid imbalance.

Quote from: Twoflower on Today at 11:33:24
About the 'Sun colour' and the 'sky colour'. That's a question I had also in my mind and feared to answer. To be honest I can't give an answer here. Probably a mixture from both. As my project is actually a try to get me awake in the winter time this is probably a question I should ask in a medic-forum.

--- End quote ---
rs20:

--- Quote from: Twoflower on September 20, 2017, 05:33:24 pm ---The RGBW sensor looks very tempting...

--- End quote ---

Another point; I'm not sure if people are suggesting taking the 4 channels out of an RGBW and using them to drive the RGBW strips? I.e., take R reading from sensor and drive red LEDs accordingly, take W reading from sensor and drive white LEDs accordingly... Because if that's what is being suggested, that's a terrible idea. Consider what happens if you ask this system to reproduce a pure red laser. Both the R and W channels of the RGBW sensor will respond, and therefore both the Red and White LEDs in the strip will light up. But this is obviously the wrong thing to do; the best impersonation an RGBW strip can do of a red laser is to turn the red LEDs on only. Turning the white LEDs on as well would just wash out the colour.

This is why it's preferable to use some sort of basic feedback or calibration/characterisation; and once you're doing that the W channel of the sensor is of very little value.


--- Quote from: Twoflower on September 20, 2017, 05:33:24 pm ---One of the problems of a cam might be the dynamic range of a prosumer/consumer cam (like the EOS D5 Mk3 that is floating around here). Starting a the blue hour running until the sun is reasonable above the horizon is probably too much. So you need to take care there too. Not impossible but something you need to take care of.

--- End quote ---

Fixed ISO + Aperture, but leave the camera to choose a shutter speed. Check the EXIF data to compensate. Also, whether you actually want to be matching the brightness of a real sunset is questionable; I highly doubt that your LED strips can compete with direct sunlight. So you're going to want to deliberately compress your dynamic range anyway.


--- Quote from: Twoflower on September 20, 2017, 05:33:24 pm ---Thanks for the heads up with the non linearity of the standard colour system. One more reason to use the RGB sensor. You can keep the whole flow relatively controlled.

--- End quote ---

Meh, I'm suggesting just calibrating the whole RGBW strip + camera filters + RGB transform as a single black box -- that's the beauty of this approach, you don't need to tease these things apart at all.


--- Quote from: Twoflower on September 20, 2017, 05:33:24 pm ---The only pitfall here I see is the room-calibration. In case the LED colours don't match reasonable with the filters of the sensor.

--- End quote ---

No, you explicitly don't need to worry about this! That's what the calibration is for. As long as you trust that your eyes have the same response as the digital camera; everything else is sorted.

But hey, whatever floats your boat. I guess it's plausible to claim that the response of the RGB filters of the chip recommended earlier (just ignore the W honestly, it extends way too far into the NIR) are closer to that of the human eye than the filters on a typical digital camera. And there's nothing inherently wrong with using the sensor, it's just that it feels to me like a lot more work.
cdev:
Don't LEDs also work in reverse, so to speak, with their maximum sensitivity being at the color they emit light at?
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