Circadian Lighting

Hello everybody,

For quite a long time I have been really interested in circadian lighting and quite disappointed for not having any software to evaluate it. Las weekend I found this release from the Solemna guys

And I was wondering if there is any intention to incorporate something similar in honeybee anytime soon, because it would be great!


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Hi @JuliaT,

Please chek this from @MingboPeng

Hi Devang,

Thanks for that. It is an interesting workflow, quite similar to one I tried to made sometime ago.
My problem with it is its conversion from lux to melanopic lux. I know he is following the suggestion of WELL about multiplying luxes by 1.1 for daylight. The problem is that as soon as you read a bit this is not realistic.

First of all, considering that the test points would only be affected by daylight is, in my opinion, too simplistic for this type of research. Though you can add as many types of light as desired, the result is just 1 and its only multiplied by the “equivalency” to daylight. However, part of those luxes should be multiplied by a different factor.

Second. Though I completely understand and appreciate the good intentions of WELL of create a simple conversion as “multiply by 1.1” you just have to read 5 minutes or talk with a phd that is working on non-visual you see it is not as simple as that. Maybe my research was too superficial but I don’t know where this 1.1 is coming from and looks rather arbitrary.

Third. The materials are still set as normal radiance ones, meaning, only photopic properties and not melanopic ones. To be completely honesty I haven’t researched about the difference between them, but, it is there.

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Hi @JuliaT,

This captures your concerns well and I could not agree more. I remember the time Solemna made the announcement in 2017 right after the announcement of the Nobel prize in Medicine. At that time, I could not find much material as how they are incorporating in a workflow. If you happen to know some publicly available source to share, I am sure it will be appreciated.

For anyone interested in knowing more about Alfa, here is the link for the presentation from DIVA Day (this was shared on their website).

Circadian lighting is still the wild west of daylighting simulations. In the sense, that there is no singularly accepted and ratified way of performing such simulations. I do believe that Alfa is a step in the right direction.

Unless there is a PhD student or researcher lurking on this forum, who is willing to read through a body of research on neuroscience and sleep and work with us on the programming side of things, I dont foresee us being able to incorporate such functionality in Honeybee (which, unlike Alfa, is a free software).

Hopefully you will find someone at some point. I actually asked a friend of mine that is doing an interesting phd on non visual, but its not possible for the moment :frowning:

When I saw 81 points of sky radiance, I said, now that’s interesting, I’m working with exactly 81 points of sky radiance samples myself, measured by my advisor (Joe Kider) on the rooftop of the Frank Rhodes Hall building at Cornell between 2012-2013. I wonder why they chose 81 points exactly, since the sampling pattern is arbitrary?

Then I saw slide 52 of that presentation @sarith posted . And Tohsing’s on the next page.

Kider Jr, J. T., Knowlton, D., Newlin, J., Li, Y. K., & Greenberg, D. P. (2014). A framework for the experimental comparison of solar and skydome illumination. ACM Transactions on Graphics (TOG), 33(6), 180.

Tohsing, K., Schrempf, M., Riechelmann, S., & Seckmeyer, G. (2014). Validation of spectral sky radiance derived from all-sky camera images-a case study. Atmospheric Measurement Techniques 7 (2014), Nr. 7

I’m using this exact spectral data myself, but on a different (non-rendering) project at the moment. Perhaps if I find out more about circadian lighting I could help…

As far as I know, whatever it is that they are doing with Alfa, specifically with regards to their workflow, is proprietary. So reverse engineering and disseminating portions or whole of that, however easy or difficult that may be, is unethical (and most likely illegal too).

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And nobody suggested that on this thread.

What I found interesting was they said they used 81 points of sky radiance distributions for their solution, and referenced Dr. Kider’s paper… with 81 points of sky radiance measurements in it. That data was hosted online by Cornell’s graphics group for about 5 years, and of course the paper is open science. Even the Bruneton paper cited in their slideshow “is based on ground-truth measurements of a real clear sky made by Kider et al.” So unless the MIT group measured their own 81 points of sky radiance (not the materials with a spectrophotometer) (which undoubtedly they would have presented in that slideshow), then that’s interesting is all I said.

Anyway, as you know I’m new to daylighting simulation myself, and have my own research and work to consider. But as a supporter/promoter/developer of open source software myself, if someone schools me on circadian lighting (which seems to be a thing), long term I’d be happy to help when I have the time.

Right now there are no agreed upon ways to do these kinds of calculations.

More here:
As Jim points out in the above comment, any new way of calculation is likely to be met with skepticism.
There arent many takers in the scientific community for what passes as mainstream Circadian Lighting calculations right now.

Mark Rea and Mariana Figueiro are from the Lighting Research Center and along with researchers like Jennifer Vietch, Christoph Reinhart (of Daysim and Alfa), John Mardaljevic etc. will have a definitive say in any standardization effort. That might be a few years from now and just like CIE 171:2016 or CIE S 011/E:2003 will likely provide a framework for making the calculations accessible to everybody.

The LARK tool, which was developed a few years ago uses a better approach than what is suggested in the WELL guideline. However, it relies on CIE skies, which were proposed for luminance and photopic, and is likely less “accurate” than Alfa would be. I am not aware of any other projects.

Understood. Thanks, @sarith.

In regards to original poster’s interests/research, hopefully that consortium comes to some agreement sooner rather than later. In this particular case, it sounds like there just aren’t any good proposed public solutions yet.

Off topic Ladybug Tools philosophical discussion -
Not every algorithm/calculation has to be standardized / collectively agreed upon to be included in an open-source toolkit. Though I agree that it’s a good idea to include the most respected algorithms for this sort of stuff. But in my experience, and as you are well aware, the newer the research is, the more approaches/ways/theories there are to account for it, in any field. Very often these same scientists on the committees are the same ones who have proposed their solutions to such problems. And typically standardizations between these approaches take many years to come to fruition, after which the proprietary solutions/companies have made money, and the public deals with the lag. Ladybug Tools looks like the best open source alternative for solutions in this domain (to my very limited experience/knowledge of it). So it seems like it is not out of scope for you guys to want to include various solutions however you see fit, in interests of supporting the latest research (as it becomes available of course) (and as you have time/resources to support such open-source software of course, which agreed is a huge factor). Aaaaaand I’m totally not complaining here, just discussing with lots of respect for you awesome peeps who have contributed so much time with this fantastic product :slight_smile:

Back to the issue of maintenance which is already started to be a major concern I think we should follow what other open source projects like d3js started to implement and that’s breaking down the development into core library and plugins. Even Mike did it wrong for D3 version 3 and it took rewriting everything for version 4 to make this happen. Our new development with the [+] libraries can support such decoupling.

I have the same question as what @sarith brought up. I know that there is a hype about circadian lighting but how does it really help for designing better buildings? And I’m asking this as a person who doesn’t know the answer. I personally would like to know why should we use such a metric? and would we use it if it wasn’t part of WELL requirements?

[…my comments about WELL and what they have been doing goes here… :confounded:]

That said if someone wants to start the development for circadian lighting simulation I will be more than happy to reply to any questions about the best practice for integration to the current Honeybee library. :smiley:

PS: This is also a good read:

Again, you all know way more about this field than I, but here is one (of maybe many(?) studies?) (I honestly have no idea, this isn’t my expertise) that are claiming occupant benefits (and thus should be considered in building design, no?). The paper doesn’t contain the keyword “WELL”. It’s from 2007 and I have no idea of its validity; just sharing as I came across it literally today. This was cited by a colleague today in a paper that has nothing to do with circadian lighting. Their reference section looks a little light, but their experiment may be valid?

Obayashi, Fumiaki, et al. “Development of an illumination control method to improve office productivity.” Symposium on Human Interface and the Management of Information. Springer, Berlin, Heidelberg, 2007.

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Hi @mostapha. This is my personal opinion, but, I think that at the moment daylight performance is just quantitatively measured and quite in a vague way if you ask me. Adding other concerns, such as circadian lighting, starts driving us to explore qualitative data or other metrics that would add an incredible value to our analysis.

I personally disagree with the thresholds of 300luxes and so on that we have to design for constantly. If we consider only quantitively, yes, we need that number, but then you conduce surveys and see that the perception of that amount of luxes vary a lot depending on the quality. I personally performed a survey for my dissertation in which people was feeling having enough light with 100 lux and not enough with above 400lux, and that was depending on the quality. Sadly I didn’t have the tools to properly measure these facts more than my opinion. And I know circadian lighting does not measure quality, but I think it increases the value of the analysis and pushes in the right direction.

For the question if we would use it if it was not for WELL certification my answer is yes. I would totally apply it to analyse buildings for sensitive people, like hospitals, care homes for people with dementia, nurseries, schools… maybe not so much for regular office buildings or houses, but yes for areas with more strict or sensitive requirements, in which, by the way, we cannot apply WELL yet.


Hi @JuliaT, Thank you for taking the time to reply.


S. F. Rockcastle, M. Danell, L. Petterson, and M. L. Ámundadóttir. The Impact of Behavior on Healthy Circadian Light Exposure Under Daylight and Electric Lighting Scenarios, ACEEE Summer Study on Energy Efficiency in Buildings 2020, Pacific Grove, Aug 16 – 21, 2020.

Potočnik, J., Cadena, J. D. B., Košir, M., & Poli, T. (2019, July). Occupant perception of spectral light content variations due to glazing type and internal finish. In IOP Conference Series: Earth and Environmental Science (Vol. 296, No. 1, p. 012033). IOP Publishing.

Hello community.

I reopen this post because I have to simulate a project for Well and Breeam and I am testing Honeybee for this.

About circadian lighting I found this video really complete from CIBSE and I want to share:


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Now, are there components in ladybug-honeybee to implement rhythmic lighting evaluation?