[Radiance-general] Gendaylit command

[Krystyna Zelenay]

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