[Radiance-general] Gendaylit command

[Reinhart, Christoph]

Dear Krystyna,

The DIAV-for-Rhino input for gendaylit is not ideal right now but we are
working on it. If you have measured global solar radiation that you want
to use to generate a Perez sky using gendaylit, you can - for example -
use a little program called 'gen_reindl' that comes with Daysim. Just
open a DOS command and type 'gen_reindl' and you will get a description
of the required input and resulting output file formats. The output
direct and diffuse irradiance are what you have to enter into the DIVA
dialogue box. As the name suggests, the program uses the 'Reindl model'
to generate direct and diffuse irradiances for global irradiances
(http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V50-497TD1G-
1GR&_user=10&_coverDate=12%2F31%2F1990&_alid=1682991794&_rdoc=3&_fmt=hig
h&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5772&_sort=r&_st
=13&_docanchor=&view=c&_ct=5&_acct=C000050221&_version=1&_urlVersion=0&_
userid=10&md5=40baa0c089e7bf9f8f3a02f4581aafbe&searchtype=a) . The model
is not necessarily the 'best' model available any more. But, when I
wrote the program about eight years ago and it did a convincing job for
a site in Ottawa. 

I hope that this helps.

All the best,

Christoph

-----Original Message-----
From: Krystyna Zelenay [mailto:kzelenay at berkeley.edu] 
Sent: Wednesday, March 16, 2011 3:12 AM
To: Radiance general discussion
Subject: [Radiance-general] Gendaylit command

Hi,

I am trying to define a clear and overcast sky for a particular
location using gendaylit. I have collected global horizontal exterior
illuminance data, but no diffuse illum. or irradiance data, so I would
thus like to use TMY3 data. I am using DIVA-for-Rhino which requires
an input in W/m2 for gendaylit, so I have two options:

a) use the direct and diffuse horizontal irradiance values from the TMY3
file
b) divide the direct and diffuse horizontal illuminances by 179 lm/W
to obtain the irradiances

Which of these is the correct input for gendaylit?

What is the significance of the luminous efficacy used in Radiance
(179 lm/W)? The book "Rendering with Radiance" states that luminous
efficacy can vary from 50 to 150 lm/W depending on the type of sky or
light considered (p357). And indeed when I divide for example, diffuse
horizontal illum. data by 179, the irradiances I get are quite
different from those in the TMY3 file.

Does this mean that I should use the irradiance data from the TMY3 file?

Thanks,

Krystyna Zelenay




from the site (but not irradiance data).The default DIVA input is in
terms of
direct horizontal irradiance (W/m^2) and
diffuse horizontalirradiance (W/m^2)

Is there a way to change the default input to

NORMAL horizontal ILLUMINANCE (lm/m^2) and
diffuse horizontal ILLUMINANCE (lm/m^2)
(i.e. similar to the -L option in the gendaylit command)

Alternatively, does anyone know how to go about converting illuminance
to irradiance data?

Thank you,

Krystyna

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