[Radiance-general] illuminance on external facade

[Jill Dalglish]

Just to muddy the question a little more, why do the TMY3 files report 
illuminance in lux but efficacy in lms/Watt?

On 3/28/2013 8:24 AM, radiance-general-request at radiance-online.org wrote:
> -----Original Message-----
> >*From: *John Mardaljevic [j.mardaljevic at lboro.ac.uk]
> >*Sent: *Monday, March 25, 2013 03:44 PM Mountain Standard Time
> >*To: *radiance-general at radiance-online.org
> >*Subject: *Re: [Radiance-general] illuminance on external facade
> >
> >Hi Ery,
> >
> >Tinkering with the Boise TMY3 data I was a little surprised to see how
> >some of the efficacy values turned out.  For those unfamiliar, the Boise
> >TMY3 climate file (much like many of the others from the Energy+ website)
> >contains both illuminance and irradiance data for these quantities:
> >
> >- Global horizontal (Gh)
> >- Diffuse horizontal (Dh)
> >- Direct normal (Dn)
> >
> >Sometimes illuminance data is derived from irradiance measurements, though
> >nowadays it is more likely to be measured separately.  Which it is could be
> >identified in the climate file (I haven't checked).
> >
> >The following table shows how the mean luminous efficacy (within 5klux
> >bands of global horizontal illuminance) varies for: the global horizontal;
> >the diffuse horizontal; and, the direct normal quantities:
> >
> >gh_lo           gh_hi      Eff_gh          Eff_dh          Eff_dn
> >
> >        5000.00      10000.0      106.145      135.606      60.1583
> >       10000.0      15000.0      106.610      147.202      73.0784
> >       15000.0      20000.0      107.339      258.167      81.6775
> >       20000.0      25000.0      108.312      140.848      88.2379
> >       25000.0      30000.0      107.261      156.417      92.4818
> >       30000.0      35000.0      106.713      184.455      94.1426
> >       35000.0      40000.0      106.456      197.996      96.1488
> >       40000.0      45000.0      106.142      213.014      97.9623
> >       45000.0      50000.0      105.894      177.705      99.2376
> >       50000.0      55000.0      105.992      173.584      100.170
> >       55000.0      60000.0      105.812      179.285      100.867
> >       60000.0      65000.0      106.057      300.989      101.701
> >       65000.0      70000.0      105.593      129.234      101.205
> >       70000.0      75000.0      105.347      145.367      101.420
> >       75000.0      80000.0      105.333      193.799      101.418
> >       80000.0      85000.0      105.044      135.980      101.445
> >       85000.0      90000.0      104.697      134.219      100.965
> >       90000.0      95000.0      103.924      123.413      100.588
> >
> >The global efficacy value (Eff_gh), as you noted, is between 100 and 100
> >lm/W -- I'd expect global vertical to be very similar to global horizontal,
> >at least for sun illuminated orientations.  Direct normal efficacy across
> >the ranges is also pretty much how I expected it to vary.  However, diffuse
> >horizontal efficacy seems to flap-around quite a bit -- four maxima, two of
> >them quite conspicuous.  I wouldn't have been too surprised to see general
> >trends, but this was unexpected.  Can't say that I've noticed or given much
> >thought to it before, but I am a little intrigued by those high values,
> >i.e. > 200 lm/W.
> >
> >Best
> >John
> >
> >    John Mardaljevic
> >Professor of Building Daylight Modelling
> >School of Civil & Building Engineering
> >Loughborough University
> >Loughborough
> >Leicestershire
> >LE11 3TU, UK
> >
> >Tel: +44 1509 222630 (Direct)
> >Tel: +44 1509 228529 (Pam Allen, secretary)
> >
> >j.mardaljevic at lboro.ac.uk
> >http://www.lboro.ac.uk/departments/cv/staff/profile/367.html<http://www.lboro.ac.uk/departments/cv/>
> >
> >Personal daylighting website:
> >http://climate-based-daylighting.com
> >
> >
> >_______________________________________________
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> >Radiance-general at radiance-online.org
> >http://www.radiance-online.org/mailman/listinfo/radiance-general
> >
> >

-- 

*Jill Dalglish, LEED AP BD+C*

S/W/DBE Certified Business
www.dalglishdaylighting.com <http://www.dalglishdaylighting.com/>
303-955-4945

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