[Radiance-general] Daylighting metric for outdoor spaces

Wed Nov 30 17:27:27 PST 2011

Hi Andy,

Thank you for clarification and explanation. It was so informative.

I agree that using hours of sunshine (sunlight hours) in this way totally
make sense however in the code I mentioned it was a metric for building
envelopes (e.g. two hours of sunlight hours in 21st December is needed for
residential buildings).

As you said the weakness of metrics like VSC or Daylight Factor
(SC+ERC+IRC) is not being climate-based and orientation sensitive but maybe
this is the best possible way for now.

Thanks,
Mostapha

On Wed, Nov 30, 2011 at 12:18 PM, Andy McNeil <amcneil at lbl.gov> wrote:

> Hi Mostapha,
>
> BRE has a metric - Vertical Skylight Component - for what you describe.
>  It is intended as a planning tool to insure that housing blocks are not
> located to close together.  It is also used in rights to light litigation
> in the UK.  It's independent of climate though, it's mainly to ensure that
> an appropriate percentage of daylight is made available at the window (i.e.
> not too many tall buildings nearby).  I'm not saying it's a great metric,
> but it's commonly used for what you want to do.
>
> VSC is commonly coupled with the hours of sunshine in a courtyard metric
> you mentioned in an earlier email.  I just want to point out that this is
> not a daylight metric but a planning tool to ensure that courtyards are not
> more damp and dank than an open park in the same climate.  For example, if
> you have a week of damp overcast weather both your open space and your
> courtyard will be damp, but then when you have a day of sunshine your park
> will dry up, but your courtyard may not if there isn't sufficient sun
> penetration.  A courtyard that stays damp gets even worse in the next week
> of wet weather.  The metric is intended to prevent mold, mildew and
> perpetually damp courtyards.  So in reality this metric is more applicable
> to climates like London and Seattle than Phoenix or Dubai.
>
> Andy
>
>
>
> On Nov 30, 2011, at 9:31 AM, Mostapha Sadeghipour wrote:
>
> Hi John, Michael, et al.
>
> Michael,
>
> Sorry if it wasn't clear enough. I think you get the concept. Yes! I
> wonder if there is a number to determine the outdoor illuminance to provide
> enough illuminance level inside. What you are saying is true and the
> effective parameters are much more than only VLT and ceiling reflectance
> but if I want to consider all of them I should modify the geometry and run
> the lighting simulation.
>
> The way I did the ray-tracing in my mind was the simplest possible
> backward ray-tracing. I started from the sensor inside, then traced only
> one ray upward and bounced it from the ceiling to the glazing. So
> illuminance level inside the space is equal to illuminance level outside
> the glazing (on the envelope of the building that I can simulate) multiply
> by VLT of the glazing multiply by the reflectance of the ceiling. In this
> way I can make a target for the illuminance level on the envelopes rather
> than indoor.
>
> The question could be more general though and thinking about the relation
> between outdoor illuminance level and then the external envelopes.
>
> John,
>
> Thank you for the great link! This is exactly what I'm talking about. I
> actually ran the accumulative annual study. That's true that cumulative
> result shows you get less illuminace in more dense areas but what are the
> cutting levels? Do we have the concept of over-daylit for outdoors?
>
> For example if I calculate the availability of useful daylight illuminance
> based on 100 lux and 2500 lux for working hours and calculate the result
> based on the percentage of hours a large portion of the well-daylit outdoor
> spaces will be considered as over-daylit because they receive more than
> 2500 lux, and then the more dark outdoor spaces located in Seattle or
> London (hi Rob!) will be assumed as well-daylit since they will be in the
> range. We already knew this is not true and the spaces next to an outdoor
> space with 150 lux horizontal illuminance level cannot be well-daylit.
>
> Maybe we can say there should be no upper-limit for outdoor illuminace
> level since we can always mitigate the light level by building envelope
> design, but what is the lower limit then?
>
> Best,
> Mostapha
>
> PS.1: I liked the concept of "warm shade" so much. So interesting to think
> about.... Can you send me a link to the paper or any other resources?
>
>
> On Wed, Nov 30, 2011 at 10:26 AM, John Mardaljevic <jm at dmu.ac.uk> wrote:
>
>> Hi Mostapha,
>>
>> > For an urban design study I wanted to avoid measuring light levels
>> inside the buildings as far as possible.
>>
>> How about using cumulative values, say annual or maybe monthly?  You
>> could also look at just the hours of occupancy.  Some examples here:
>>
>> http://www.iesd.dmu.ac.uk/~jm/doku.php?id=academic:urban-solar
>>
>> The image for London clearly shows the effect of tall buildings reducing
>> the ground level cumulative illuminance (actually, irradiance in the legend
>> but just x 100 to estimate klux-hrs / yr).
>>
>> Best
>> John
>>
>> Reader in Daylight Modelling
>> Institute of Energy and Sustainable Development
>> De Montfort University, The Gateway, Leicester, LE1 9BH, UK
>> Tel: +44 (0) 116 257 7972
>>
>> jm at dmu.ac.uk
>> http://www.iesd.dmu.ac.uk/~jm
>> http://dmu.academia.edu/JohnMardaljevic
>>
>>
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