[Radiance-general] illuminance on external facade

[Andrew McNeil]

Ery,

German is correct.  179 lumens/watt is the efficacy for uniform
distribution of visible light.  And only useful after you've converted to
visible energy.

The efficacy for the solar spectrum varies based on properties of the
atmosphere (which is constantly changing).  The efficacy for direct sun is
generally 80-120 lumens/watt.  The efficacy for sky is typically 100-140
lm/watt.  The efficacy of light on a facade is further complicated since it
is a constantly changing mix of direct and sky.

Sorry I can't give you an easy number!

Andy


On Wed, Mar 20, 2013 at 3:36 PM, Germán Molina Larrain <gmolina1 at uc.cl>wrote:

> Dear Ery,
>
> the 179 is the magic number just for Radiance... is the Luminous Efficacy.
> My understanding is that the Luminous Efficacy of the clear sky is around
> 100; but it vary.
>
> My answer would be NO. But wait for others, there might be some hope yet.
>
> Regards,
>
> German
>
>
>
> 2013/3/20 Ery Djunaedy <ery.mailinglist at gmail.com>
>
>> Folks,
>>
>> This may not be a relevant question for Radiance list, but I ask it
>> anyway.
>>
>> If I have the solar incident (irradiance, direct and diffuse) on the
>> external facade, is there a simple way to calculate/estimate the
>> illuminance on the facade? The magic number 179?
>>
>> Thanks,
>>
>> Ery
>>
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