Realistic view of sunlight inside a room

[Anonymous]

Hi. I have developed a model of a house and set the location parameters so it is in the correct place and orientation. I want to get a realistic view of how dark/light the interior rooms will be without the use of artificial lights. Basically if I was standing in the room with the lights off what could I expect in terms of natural light the room. I understand that this changes over the day. However when I render even in mid day the main room on the 1st floor looks very dark. 

I can see that there is a lighting setting in the render dialog. It gives options for interior and exterior sun. Switching between these two has a dramatic effect on the light in the room. The problem is I cant find anywhere that explains the difference between them. Is the "interior sun only" the setting for internal rooms to show the impact of natural light in the room? 

I would be very grateful for any advice to get me to a position where I am confident that the renders give a true reflection of the natural light that will be in the rooms. I don't want a big surprise and find it is totally different when we build/renovate the house.

I have added renders using internal and external sun only (taken at same time summer solstice) of the main room on 1st floor and included the project in case it might help. 

Many thanks

Tony

[RDAOU · Accepted solution]

@Anonymous 

The analysis should be fairly accurate and realistic. If you have used all the proper material in your model! Producing a photorealistic render to match 100% those lux levels is a different story and I cannot really say if there are other software that can guarantee that...you can check with Enscape or Lumion

You could also check on the Insight Lighting and Solar analysis forum … they will be able to give you more insight of how accurate and realistic the cloud analysis  and rendering can be and whether it is possible to achieve a 100% match.

https://forums.autodesk.com/t5/lighting-solar-analysis-forum/bd-p/19 

[Anonymous]

Thank you again for the help and advice.

[RDAOU]

You're welcome

[barthbradley]

Luminescence??? That's a heck of a curve-ball you throw!  How does that relate to Rendering in your mind's eye?   

[Anonymous]

I was being guided by the responses in the posts. It was suggested this was a better way to see the effect of natural light. I have no real understanding on the subject. I am just trying to see if the design makes sense or if we create a dark cave. 

[scheerd · Accepted solution]

Unfortunately the visual Rendering engine doesn't use actual weather data (DHI and DNI solar values) or the same Perez Sky Model like the illuminance Rendering option. 

The internal sky model when running normal image jobs use a modified Preetham sky model, whereas energy/Illuminance jobs use the Perez radiometric model and user-supplied solar values for DNI/DHI.  The latter is the same used by the Insight Lighting tool.

Here's an interesting article on the Preetham model with images and discussions of other sky model types like Perez, CIE, etc:

https://www.semanticscholar.org/paper/A-Critical-Review-of-the-Preetham-Skylight-Model-Zotti-Wilkie/...

You can get pretty close between 'normal' and Illuminance if you follow these steps:

1. Set your Location and select a Weather File from the Manage > Location dialog.  Be sure to use the Internet Mapping Service option, and select a weather file from the list to the left of the map.  Best to choose a station with a 'year' of '2010', as those are standard TMY stations that will have solar values fairly close to the standard visual Rendering values.
2. Open Insight Lighting, select Run New Analysis, and click Go.  We won't be kicking off a run, just using data available in the UI.
3. Select Illuminance Analysis type, then click the '...' button in the Environment section.
4. Choose a Perez Sky Model, set the time you want to visualize, then choose a date within 1-2 weeks of the date you want to visualize that has '0% sky cover' (clear sky).
5. Note the values for DNI, DHI, time and date, and cancel out of the Lighting dialogs (or Start Analysis if you like)
6. In the Rendering Settings of the View, choose Interior: Sun Only, then click the '...' to open the Sun Settings.
7. Ini Sun Settings, choose 'Still' in the Solar Study section, then enter the Date and Time you noted earlier.  Click Apply and OK.
8. Use Render In Cloud to kick off a visual rendering.
9. Use Render In Cloud again and select the 'Illuminance' Output Type.
10. In the Location/Time tab, select either 'Use date from view' or enter the date and time you noted before.
11. In the Sky Model, choose the Peres Sky Model type, and enter the DNI and DHI you noted before from the Lighting Environment dialog for a clear day.
12. In the Legend, I prefer to use a fixed legend so I can compare different times and dates with the same scale. For interior illuminance and range of 0-100 or 0-200 Footcandles, non-logarithmic is a useful range.

While that won't be exactly the same as each other, they'll be pretty close.

David

[Anonymous]

Thank you for the detailed instructions. I just had a couple of clarification questions:

1. I am still confused about the difference between lighting settings; interior sun only and exterior sun only. I think I asked the wrong question previously. I don't actually understand the basic meaning of these 2 settings. Are they both rendering the natural light from outside the property? one should be used if you render internal to the structure and the other if you are rendering outside the property? The reason I ask is because of the huge difference in results between the 2 settings. I am concerned if the internal sun only is a "fake" representation based on something like there being no roof and so full sunlight inside. I hope this question makes sense. 

2. Does the render in cloud use the location and lighting settings from the desktop to control the rendering in the cloud? I had missed this point.

3. I think you are suggesting 2 cloud renders. A normal photo and a Illuminance' Output Type (as I attached to the post but did not take the steps you outlined). How do I compare the 2 outputs? Is it that if the average lux is 1500 (green) in the illuminance output the picture shows what that looks like as a picture.

Just to clarify about my request for a realistic render. I am not concerned about accurate weather conditions. It is really a question about the impact on the large terrace we have put in front of this room. I have attached a view of the terrace. 

Many thanks

Tony

[scheerd]

1. I'm not sure the exact difference between the two.  In my experience they always yield the same results.  While Insight Lighting uses the Rendering engine, we use a lower-level part of the engine where we have control of all the parameters, while Render In Cloud adds a lot of front end automation.  You should pose the question to the Rendering forum: https://forums.autodesk.com/t5/rendering-forum/bd-p/2060. 
2. Render In Cloud does not use the weather file solar values for visual renderings, nor does it allow you to set those parameters.  Even if you use an illuminance output type you need to define the DNI and DHI manually.
3. The relative distribution should be about the same if you define clear sky solar values for illuminance run, but as they use different sky models, the results are not exactly comparable.  Also with a visual rendering, settings like exposure, etc will significantly change the visual image.  A visual rendering is a visualization of 'luminance', which is light coming off of the surfaces to your eye.  An illuminance rendering is a visualization of 'illuminance', which is the light falling on the surfaces.  The amount of illuminance that turns into luminance depends on the reflectivity of the surface as well as how your eyes adjust to the light.

You might consider checking out a tool like LightStanza that uses Radiance and will allow you to generate a false-color luminance image and do glare analysis.

If you're looking at the effect of a design change, the best thing is to compare two images with the same settings, as the difference is what's important.

David

[Anonymous]

Thank you once again for the detailed response.

I feel really bad as I must be asking my question is such a bad way (it is my ignorance). I wanted to understand whether I should be using Scheme: interior sun only or Scheme: exterior sun only. They give completely different lighting. Is the Scheme interior sun the correct one to use to get a "realistic" view of the impact of being in the room without artificial light? If so then when would you use  Scheme: exterior sun only?

The link you provide does not seem to work for me.

Many thanks

Tony

[ToanDN]

My test shows Exterior Sun Only and Interior Sun Only producing vastly different results given every other settings are the same.  I think Exterior does not calculate light bounces in the space.

[scheerd]

Not my domain.  Please contact the Rendering Forum:

https://forums.autodesk.com/t5/rendering-forum/bd-p/2060

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