# Blinds/shades operation in sDA calculation

**URL:** <https://discourse.ladybug.tools/t/blinds-shades-operation-in-sda-calculation/2546>\
**Category:** honeybee\[+\]\
**Created:** [December 26, 2017, 3:31pm UTC](https://discourse.ladybug.tools/t/blinds-shades-operation-in-sda-calculation/2546 "2017-12-26T15:31:43Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![mostapha](https://discourse.ladybug.tools/user_avatar/discourse.ladybug.tools/mostapha/32/15244_2.png) [@mostapha](https://discourse.ladybug.tools/u/mostapha)\
**Post date:** [February 7, 2018, 6:19pm UTC](https://discourse.ladybug.tools/t/blinds-shades-operation-in-sda-calculation/2546/5 "2018-02-07T18:19:23Z")

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@Mathiassn and @MingboPeng,

I read both links and reviewed the IES LM-83-12 document. Thank you both for sharing your thoughts and resources.

We can automate the process of generating blind states with what we currently have implemented in Honeybee[+] however there a couple of design decisions to be made. There is also a concern about the Grasshopper performance when the number of analysis points starts to be more than a couple of 1000, and the number of window groups are more than a couple of dozen.

Honeybee[+] calculates the direct contribution of sun separately from the diffuse sky which means there is no limitations for calculating the times when more than %2 of analysis points in each grid receive more than 1000 lux from direct sun. The question is how to calculate the blind combinations effectively.

Currently you can input/design the blind states when creating the case using window groups and blind states but I’m thinking to add another scenario which let you test the scenarios of _desired_ dynamic blinds and study what will happen if you block a certain % of direct and sky/diffuse contribution. It seems to be more inline with what IES LM-83-12 section 2.2.7 describes:

> “If BSDF data cannot be used, and the windows have fabric shades or curtains, model the shades using  
> a combination of specular and diffuse transmittance. The specular transmittance should be equal  
> to the openness factor of the fabric, while the diffuse transmittance should be the total visible light  
> transmission (VLT) minus the openness factor. If the VLT is known and the openness factor is not known,  
> model the VLT as diffuse transmittance only. If the shade VLT is unknown, model the shade using 5%  
> diffuse VLT with no specular transmittance.”

> “If BSDF data cannot be used, and the windows have white louver blinds (\>80% reflectance); use a 20%  
> VLT diffuse distribution for both sunlight and skylight. The VLT of darker blind colors shall be depreciated  
> proportionally, to a lower limit of i 0% diffuse VLT for black blinds (reflectance of 0%) for both sunlight and  
> skylight. Thus, blinds with 40% reflectance should be modeled at 15% VLT, while 60% reflectance should be set at 17.5% VLT, etc.”

Finally for addressing the possible performance issues for loading data, and several other reasons, we will be pushing the data from the analysis to a database which will make these calculations possible efficiently.

Let me know your thoughts and if this satisfies what you’re trying to achieve.

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