Looking for RGB or RGBW values of a sunrise - Page 1
Forum section: electronics / general

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 17, 2017, 07:53:12 pm
content: For a small project I need a table of RGB or RGBW values over time of the sky-color from the morning just before the sun rises until the sun is nicely over the horizon**. In the end I would like to play back this using a LED strip. Actually two strips: One RGB and one white. Thus the RGBW. But I think I can convert an RGB table to RGBW.As I don't have a single pixel RGB sensor I need to find another way. My idea so far was to setup a cam looking into a white, opaque globe to get the sky colour as whole. Do a picture every minute or so. And reduce the rescale the picture to 1x1 pixel to further obscure the light and get the RGB value from the sky from that remaining pixel.Any other ideas, or is there somewhere an existing table I can use? An existing table would be nice as here thewinterfall is coming and the chances to capture this is not that high any more.**I'm speaking of a rising sun as seen from Earth. And a nice one is preferred ;-)

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 17, 2017, 08:35:14 pm
content: Thanks evb149.As I said, I'm looking for aniceone. So a location with low particle count (including water). OK, the longitude and altitude wasn't specified. So the altitude should be about sea level (I like the reds of the rising sun). About the latitude: Here I'm probably not that picky, lets say somewhere in the range of +/-50° would be acceptable. To my understanding that mainly changes the speed of the phases and I can adjust that. The sun position should be between 8° below horizon (blue hour) and 15° above horizon (novisiblereddish sky any more). Looking at all the data, couldn't be a simulation a source of this table?Using the white balance and lux value is some kind of different scale which should be possible to transform into the requested RGBW table. But one or two values are not enough to calculate a nice transition between the points. And so far I haven't found any table that provides more than 2 or 3 values unknown how they timely relate. That's the reason why I'm looking for a higher resolution on the time axis. Probably 20 entries are enough to extrapolate the steps in between. I wouldn't complain if I can get more steps.About the dynamic range. That's also right, I'm limited to 12bit resolution per channel. And that's plenty for my application. Probably except that the lower end might be still to bright for my taste.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 18, 2017, 04:41:19 pm
content: Thanks again evb149.I scanned through the papers. And that provided the right keyword in one of them: "CIE daylight model". Even if the model needs to be purchased it can be used as Google search term. Lots of interesting information pops up. Including a Daylight Visualizer from a company producing windows (free download). Probably I need to play with it to see if I can abuse it and model a integrating sphere instead a room with windows.

author: ajb
author_rank: Super Contributor
timestamp: September 18, 2017, 05:50:09 pm
content: Quote from: Twoflower on September 17, 2017, 07:53:12 pmI'm not sure integrating the whole sky will get you the effect you want, since the quality of light at sunrise is highly variant depending on viewing direction. You may get more useful information from an integrating screen aimed towards the sunrise, or perhaps multiple captures with the screen aimed at different parts of the sky. You'll also need to be careful that the white balance of the camera is fixed through the whole capture, otherwise the changing white balance will confound your normalization process.Another thing to consider is that if you are looking to illuminate a room or something with your RGBW LED strips you're going to have a very difficult time replicating the way a sunrise illuminates a scene. This is down to how the illumination spectrum interacts with the reflectance spectrum of the objects under illumination. An object illuminated by an RGBW "orange" is going to look quite different than when illuminated by a sunrise "orange" depending on its pigmentation. The only real way to do better here is to use more wavelengths--IE, instead of red, green, and blue, you might want deep red, red, orange, yellow, green, and blue. Or even more--some LED stage lighting fixtures use seven different wavelengths to achieve smooth color mixing and less erratic interactions with the pigments in the scenes they illuminate.So if you wanted to really closely replicate the illumination of a sunrise, you'd want to take a spectrograph of the sky over the course of a sunrise and then try to match that spectrum as best you could with a handful of different wavelengths (and possibly multiple color temperatures of white as well). It still wont' be perfect, but it will be far better than RGBW. Of course if you're just illuminating a white screen or something, then RGBW may be just fine.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 18, 2017, 06:27:20 pm
content: ajb: Yes you're absolutely right. The automatic setting would spoil the process. On the other side one could probably use the while balance result the Cam would use from the EXIF data. But for sure that will be the first thing I will do: Fixing the exposure settings.And I also plan tocalibratethe final setup with the same approach. Because the environment is not neutral white, but it is static. The idea is that set some specific RGBW values, taking a picture and compare what I wanted to see and what I actually get. As the equipment is very compute limited that factor will then included into the lookup table in aofflineprocess. Unfortunately I can't fit more than 2 LED stripes into the aluminium profile. So one RGB and one White has to be sufficient. then again I don't want to have a 100% replica of a 2*10^30 kg fusion reactor shining from 150mio km through 500km gaseous molecules in my home. It would be nice to come close without getting a sunburn and the heat. But so far I need some starting point with the possibility to improve the result in a iterative process.Unfortunately I don't have a spectrograph,justa Canon EOS 5DMk3. That's the reason for using this one to collecting the data. Plus the converting from the continuous result from the spectrograph to discrete RGBW values. But that is probably doable.

author: mrpackethead
author_rank: Super Contributor
timestamp: September 18, 2017, 07:55:22 pm
content: You'll not be able to reproduce it with RGBW.. You'll need to widen the pallet out, and include Amber, Cyan and Violet LEDS as well to do it accruately.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 18, 2017, 08:05:00 pm
content: As said: I have only RGBW available. So I have to live with the area I can cover with that. Again: I don't need a full spectrum rendering. Whatever I can do with the possibilities that I can build.In theory the driver circuit has two spare channels. But mechanically I can't add additional colours.

author: cdev
author_rank: Super Contributor
timestamp: September 19, 2017, 04:37:33 am
content: I like this idea..However I think the use of a diffuser is going to sell you short because youll only get the average color also finding an color neutral dome sounds well nigh impossible (if there was such a thing it would either be insanely expensive, I suspect, or likely be a gel, not a dome)The rising sun actually seems to me to at some points in time display almost all the colors of the rainbow which could be scanned in a vertical line.But its very subtle and likely only a quite good sensor would capture it. Also, those beautiful subtle shades are right at the beginning, long before the suns disk appears.The sun's light would fry your camera's sensor, so don't let that happenQuote from: Twoflower onYesterdayat 13:53:12winterfall is coming and the chances to capture this is not that high any more.**I'm speaking of a rising sun as seen from Earth. And a nice one is preferred ;-)

author: BrianHG
author_rank: Super Contributor
timestamp: September 19, 2017, 05:19:52 am
content: You want one of these:https://www.digikey.ca/product-detail/en/vishay-semiconductor-opto-division/VEML6040A3OG/VEML6040A3OGCT-ND/5168309Also, you need to approximately point it upward or better in the direction away from you viewing angle to replicate the view from that direction. Higher quality huge outdoor LED screens use them to correct their brightness & color throughout the day. High quality cameras use them to figure out what the auto white balance should be...

author: cdev
author_rank: Super Contributor
timestamp: September 19, 2017, 06:39:44 am
content: Ages ago I used to use a program called Chromatica which deconstructed an images palette in a really quite useful(for a web developer or illustrator) way.You'll lose the potential to do something much more effective if you attempt to merge all the beautiful individual colors in a sunrise or sunset into one.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 19, 2017, 04:55:19 pm
content: Ok, now we get somewhere! I haven't expected less from the forumites@evb149:I've seen the Matlab-code in the GitHub repository. But I didn't spend too much time in there. But the nature article and the github description mentioned that there the RAW information are hidden. It's on my to-do list to dig further in there. That looks promising.@BrianHG:The Vishay VEML6040 colour detector looks very nice and it's cheap too. And easy to use as the whole analogue circuit is included (I'm a digital guy; for me everything between 1 and 0 is broken). Probably I'll order few as a colleague saw it and wand two as well. That would make the final calibration much easier. But I don't plan to do a closed loop. Just a one time calibration of the environment. The recording of rising sun with this will be a piece of cake as well. I haven't expected that they are that cheap and easy to use. Except the soldering might be a small challenge. But I've managed to solder SMD devices first time right I'm not too much worried.@cdev:Unfortunately I can't manage to find the Chromatica software. There's too much noise if you enter the name plus some other keywords.@cdev:I thought about using individual LEDs to do something like the Philips Ambilight. But I decided against it as the stripes I plan to use have more power (RGB combined: 420lm/m, white: 2240 lm/m), higher density (RGB: 60/m, white: 140 LEDs/m), and the white a much better colour rendering (Ra > 80, not the best, but reasonable). So I decided to go down to a resolution of 1x1 pixel.Again thank you so far for the input. Still if someone has some additional nice ideas, hints. I'm open for any input.

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2017, 01:25:52 am
content: If you just wanted to replicate the white of the sun, not sky color, I have done a Planckian locus in the CIE 1960 UCS color temperature correction for my video scaler and I can give you the RGB correction factors for approx 9000K through 3000K, the sun at high noon being flat 100% RGB = 5000K and approximately being 3400K 1 hour before dusk and 1 hour after dawn. The adjustment is close to the human eye's visual response once a reference color is converted to RGB.IE, put an RGB color in, use the selected color temperature correction factors and get a new RGB color out.

author: cdev
author_rank: Super Contributor
timestamp: September 20, 2017, 05:08:29 am
content: You might be able to create a sunrise look with mixed dichroic light.

author: cdev
author_rank: Super Contributor
timestamp: September 20, 2017, 05:11:44 am
content: It was a Photoshop plugin for the first iteration of plugins under OS 9 mostly. The best period for plugins.

author: rs20
author_rank: Super Contributor
timestamp: September 20, 2017, 06:09:03 am
content: Ummm, why are people suggesting RGB light sensors chip? Almost everyone has a color digital camera, and the sensor of a digital camera happens to consists of millions of RGB light sensors, pre-connected to a trivial-to-use USB / SD-card interface.Your problem reduces to recording a video of a sunrise with a decent-quality camera, and then also record a second movie of your RGBW strips being run through a sequence of different values. The second movie is your Rosetta stone; telling you which RGBW intensities result in a given recorded value in the camera. Just apply that transform (some basic interpolation required) to find the RGBW intensities required to produce the same response in the camera as the sunset, and your RGBW strip will now produce output that looks identical to the sunset (at least as far as your camera is concerned; a crap camera may let you down here). It goes without saying, as mentioned by others, that we way the light distributes through the room will not be identical, just the average hue of light (depending on how you crop/average the recorded images.)If you just point an SMD RGBW sensor vaguely at the horizon, you have virtually no control whether it mixes in the blue sky above or the green grass below, which would mush away the orange of the sunrise.I did something similar once to produce an image on a computer screen that looked exactly like an apple, using a camera taking a photo of the screen to correct for the transfer functions of both the monitor and camera. I had the real apple propped up in front of the screen and it worked surprisingly well -- as in, people would be walking up to my demo from afar saying "Why do you have two apples propped up in front of a blank computer screen-- OHHH WOW". (Context: then you'd look through a hyperspectral filter and they looked totally different, ergo "look how much information your eyes are missing" etc etc.) Just a consumer digital camera and MATLAB.Just remember that sRGB is a non-linear representation; things will be seen to be behaving much more linearly if you convert back to a linear space (e.g. Nikon RAW files are in fact just 16-bit TIFFs with linear color space.)

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 20, 2017, 05:33:24 pm
content: 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 instoneOTP-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.

author: cdev
author_rank: Super Contributor
timestamp: September 20, 2017, 08:43:52 pm
content: 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 healthIts my understanding that the pineal gland is where our body's circadian rhythm is regulated.

author: cdev
author_rank: Super Contributor
timestamp: September 20, 2017, 08:58:22 pm
content: 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 onTodayat 11:33:24

author: rs20
author_rank: Super Contributor
timestamp: September 21, 2017, 01:10:47 am
content: Quote from: Twoflower on September 20, 2017, 05:33:24 pmAnother 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 pmFixed 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 pmMeh, 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'tneedto tease these things apart at all.Quote from: Twoflower on September 20, 2017, 05:33:24 pmNo, you explicitlydon'tneed 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 thechip 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.

author: cdev
author_rank: Super Contributor
timestamp: September 21, 2017, 01:32:38 am
content: Don't LEDs also work in reverse, so to speak, with their maximum sensitivity being at the color they emit light at?

author: rs20
author_rank: Super Contributor
timestamp: September 21, 2017, 01:45:28 am
content: Quote from: cdev on September 21, 2017, 01:32:38 amNo, they will respond to colors at ahigherenergy/frequency than what they emit at -- i.e., photons with enough energy to promote electrons across the bandgap or whatever (if the LED epoxy is tinted red, though, that will obviously contribute). In any case, even if the sensitivity curve matched the emission curve perfectly, that's explicitlynotwhat the OP wants -- the OP wants sensitivity curves that match the human eye, as creating an experience that matches a sunset (as seen by humans) is the aim of the game here.

author: BrianHG
author_rank: Super Contributor
timestamp: September 21, 2017, 04:30:33 am
content: Use 2 RGB sensors. 1 for the sky and the other for you LED strip. Match the color characteristics. The RGB sensor has the built in analog with temperature correction to guarantee a fixed reference reading from device to device. Also, a cheap pinhole lens may be used to capture the sky with a narrower field of view.

author: cdev
author_rank: Super Contributor
timestamp: September 21, 2017, 04:52:12 am
content: Please let us know if you capture the legendarygreen flash. (a brief moment ofgreen lightthat occurs at a specific moment during the sunrise and sunset as the light from the sun is emerging or vanishing.)

author: BrianHG
author_rank: Super Contributor
timestamp: September 21, 2017, 09:29:20 am
content: Quote from: cdev on September 21, 2017, 04:52:12 amWicked.... I've never seen that before....

author: cdev
author_rank: Super Contributor
timestamp: September 21, 2017, 03:48:15 pm
content: Indeed,Okay, now you need to see it.. how?you need to have a clear view towards the west or east. Very flat places are the best- or in an airplane. I think the reflection off the water magnifies it so you're most likely to see it at a beach alongside a large body of water.Ridgetop hiking, at sunset, I think you may have a better chance although it seems to me the inversion/blob kind of green happens less from high up.(to be honest with you I don't know the science, just trying to go from memory, sunsets from ridges while hiking=spectacular/colorful..)If you don't live anywhere near a beach, but fly from time to time, perhaps your best chance of seeing one soon is from the air?Quote from: BrianHG onTodayat 03:29:20>Quote from: cdev onYesterdayat 22:52:12green flash. (a brief moment ofgreen lightthat occurs at a specific moment during the sunrise and sunset as the light from the sun is emerging or vanishing.)Wicked.... I've never seen that before....

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 21, 2017, 05:51:23 pm
content: Sorry if my simple description from the first post was misleading. A as good as I can manage with the RGBW sources is good enough for me.@cdev:No worries about looking direct into the LEDs. It's behind my bed and cowered with a opaque diffusor.Wrt different sunrises at different locations. That's actually one additional plus for the sensor: It's easy movable and I can ask someone who travels at a nice place to do the recording.Yes I could use my camera in HDR or do some additional calculation to compensate changes of the exposure time (I would keep the diaphragm fixed). But I feel that this is rather cumbersome setup; especially as my tripod is a heavy load (Manfrotto) and I don't own a car.@rs20:About the usage of the white channel: Thanks for the heads up. It would be very obvious to get completely overblown rendering of the record. That needs to be taken care of. I noticed that extreme wide range of the W channel too. I think ill still record it and keep the data but not use it.I think a mismatch of the Filters and the LED colour might be bad. Just imagine the red LED is shifted compared to the sensor that only 20% passes the filter the RGBW sensor: The reading will be much to low and you would think you need to beef up the R channel more than necessary.I see the sensor like a small project. For both the Cam and the Sensor I need the hardware setup (opaque dome or reflector, ...) the calculation from the sensor/cam needs to be done. Here the sensor gains a bit as I have already the RAW data in a nice format. And I have several controllers flying around which are currently waiting to be used.@BrianHG:Probably I'l use one sensor which is used for both usage models. As I don't plan to compensate changes on the room I do a single calibration run to identify correction curves that are applied to the RAW sensor data on a PC. the processor might have enough CPU power to do this online. But imagine something red falls on the sensor and you will wake up under a green-blue skyThe pinhole lens sound like a good idea! Worth a try.@reen flash:(OK, that's not a user rather a topic) I've watched so many sunsets over the sea and never was lucky to see one. I was aware of this effect and hoped so many times.To my understanding a place with a view over the sea will do. And the weather conditions must be perfect: The sky must be clear and the right temperature conditions over several air layers must help to bend the light a bit around the earth surface.I'm not sure if a plane is helpful. So far I only saw pictures from it on sea level.Just for your entertainment I've added two pictures of the driver (6+1 12bit PWM channel, the MOSFETs are bottom side mounted, controller not mounted) and the LED stripes loosely placed in the profile with the opaque cover.Edit: Added Pictures

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 12:30:54 am
content: Quote from: Twoflower on September 21, 2017, 05:51:23 pmAs for the pinhole lens, you can safely point this instrument directly at the sun and it wont fry the sensor + the distance between the pinhole and the RGBW sensor controls the field of view the sensor sees of the sky. Like a zoom control, but, no focusing needed. IE, the further away from the RGBW sensor, the more narrow section of the sky falls on the sensor. The closer to the sensor, more of the sky's view-able area will be centered on the sensor.

author: rs20
author_rank: Super Contributor
timestamp: September 22, 2017, 12:48:16 am
content: Quote from: Twoflower on September 21, 2017, 05:51:23 pmThe already-stated assumption is that the Red filter in the RGB sensor has the same response as the corresponding cones in the eyes. So, if the red LED is "shifted" such that only 20% passes the red filter, then that red LED only produces a 20% (proportionally speaking) response in the red cone, and it'sexactly the right thing to doto beef up the R channel accordingly.Meanwhile, matching the filter to the emission spectrum of the LED leaves your overall system completely blind to the fact that this LED only weakly stimulates your eye's red cones, producing far too little red light accordingly. Matching the filter to the LED instead of matching the filter to the eye is exactly the wrong thing to do.The only issue that can be caused by a poor choice of LEDs is if the combination doesn't have a wide enough gamut. But since sunrises are not particularly saturated in colour (all the wavelengths are there in some quantity), I seriously doubt you'll run into gamut issues. (You'll know you've run into a gamut issue if your interpolation software turns into extrapolation software and requests anegativedrive for one of your LEDs.)

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 22, 2017, 06:57:51 pm
content: @BrianHG:Right that distance might work as zoom. But I think as the sensor is very small this will end up in a huge 'crop factor'. Probably useful distances are in the mm range. But worth a try.@rs20:Yes you're probably right as the sensor is designed to match the human eye. I missed that fact and just thought the total luminosity. So if the the LED has a strange centre wavelength the eye will be affected similar to the sensor. This should cancel it out. I checked the LED vs. Sensor wavelength. They're not that far away that this actually matter for my needs (620 vs 650nm, 520 vs 550nm and 465 vs 450nm).

author: rocketscienceguy
author_rank: Newbie
timestamp: July 07, 2020, 06:12:07 pm
content: I'm also looking for an RGB sequence of a sunrise, or, preferably, a daylight cycle. It does not need to be as precise as this original thread author intended, just an approximation for a cycle I can use as a translucent image overlay to broadly simulate day/night cycle in a game. I've read through all the postings on this thread, and it looks helpful to someone who wants to produce their own accurate and precise measurements for a particular time and place. No generic sequences were actually given, and I'm hoping that with my relaxed requirements someone would share such a sequence knowing it would be helpful.Minus a chart, I'll start experimenting with sequences. My first thought is to start from black, and then plot a path mostly along the edge of the RGB color cube: black(255,255,255)->magenta(255, 0, 255)->red(255, 0, 0)->yellow(255,255,0)-[diagonal from yellow to cyan, bypassing green]->cyan(0,255,255). I'd step through all the states between each of these vertices in a straight line, and, upon reaching the endpoint, I'd reverse the sequence.

author: tooki
author_rank: Super Contributor
timestamp: July 07, 2020, 06:26:55 pm
content: Quote from: Twoflower on September 17, 2017, 07:53:12 pmWhat makes you think that every sunrise is the same?Honestly, I don’t see the point in attempting to scientifically capture something that is so wildly variable. Just play around with values until you get the desired effect.

author: Twoflower
author_rank: Frequent Contributor
timestamp: July 07, 2020, 06:52:59 pm
content: I never claimed that all sunrises are the same. I was looking for a base-point to start of the tweaking you suggested. Especially what color do one would take: The color of the sun, the color of the sky (close to the sun, opposite, ...) a mixture of all. And also was looking for suggestions if either something like a dataset is available, a simulation tool or how to record the color composition. And I got very valuable feedback from the forumites (big thanks about that).I get every time surprised if there are implied suggestions that I want to do that scientifically correct**. I just want to re-build a kind of Phillips sunrise alarm clock. Nothing more, nothing less :-)Unfortunately the project got pushed out even further :-(** In the meantime I was visiting the PTB here in Germany. They have a scientific setup for testing solar-cells. I forgot how many different wavelengths they use. I have only a picture taken of the big setup:they had also a smaller but more accurate testbench.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 26, 2020, 01:50:53 pm
content: To provide some additional input: The latest version of the render softwareBlender(free&open source) includes a physically based sky renderer calledNishita(a bit down is a short demo reel including the source files for that setup). The code behind is documentedhere.The result looks impressive and might be a reasonable good source of daylight color transitions. Especially you can replay and modify it as you need not like using a real world measurement.

author: macboy
author_rank: Super Contributor
timestamp: September 28, 2020, 09:10:21 pm
content: Colour is funny business. By funny I mean extremely complicated.You ask for RGB values. You can't just take RGB values and drive the R, G, and B portions of the LED strip to those brightnesses and expect to get the same colour. No way. Because.. what is Red or Green or Blue? The actual specific color coordinates of those primary colours produced by your strip will not match any standard. Then there is the brightness of those primary colours produced by the strip.So even if you can convert from same arbitrary standard to something you can directly program into the strip, you have another significant problem. The R, G, and B LEDs each produce averynarrow spectrum of colors. For a display device (something meant to be viewed directly, like a TV or monitor) this can be highly desirable as it allows a wide gamut of colour to be produced. A property of the human eye called metamerism allows this spiky, uneven spectrum to appear exactly the same as any other different spectrum which happens to excite the eye's three types of cones in the same proportions. However, for a illumination source (something meant to illuminate other objects like a light bulb) this is highly undesirable, as not all wavelengths are represented in the output. Brightly coloured objects are especially affected. So while you can calibrate and tweak the LED strip to mimic any colour exactly,for direct viewing, as soon as you bounce that light off some other non-white object, it will look very different. Not even close. This includes the paint on your walls and your furniture, your skin, and everything else in the room. It will look strange.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 29, 2020, 07:12:46 am
content: Yes, there's lot of things to do to get a reasonable output. Just for the LOLs I fed the 'RAW' data taken from a set of frames to the LEDs made me wonder if I mixed up the the channels ;-). The white channels doesn't simplify things either but will hopefully improve the result as it does not have this extreme RGB-peaking. I hope to use the VEML6040A3OG color sensor to find the right relationship between the individual channels, tweak the whitepoint to get close enough to my goal. At least I think driving the LEDs with PWM provides reasonable good linearity to not run a full calibration process. And of course the setting is valid for the same type of LED combination.The light-strip will facing a wall*. No direct light. The problem with direct light to colored objects are not given. At least as close as it doesn't hurt the eye. And the plan is to use the RGB channels only to 'tweak' the whitepoint (not correct therms, but I think you understand what I mean) to the right direction. That reduces the peaking of the RGB channels to the minimum.*) Which is unfortunately not white but a light yellow/orangish color. So probably a final tuning is needed in the end.