[Bldg-sim] question regarding lighting efficiency/gains units of measurement

[Julien Marrec]

Hi,

I agree with Nick, usually the metrics used in the US concerns the Lighting
Power Density (LPD), in W/sqft, but this is also the case in most of
Europe, of course in W/m² (at least in France and I'm guessing the UK too
considering the BREEAM Standard).
Usually standards adapt to different required lighting levels by giving max
LPD per space type (to adjust for required lux levels)


Anyway, for the sake of a dimensional analysis:

1 lux = 1 lumen/W.

<=> W/(m².100.lux) = (1/100) / (W/lm)

So it is the inverse of the luminous efficacy (expressed as a percentage).

Now if you want to throw in foot-candles (1 fc = 1 lm/ft²) just for fun...
be my guest. that'd be W/(m².100.lux) = 1/100 * W / (ft².fc) but I have
never seen that being used...


(I can't resist the opportunity to say it'd be about time to start using
the SI units in the US too :))

Best,
Julien

--
Julien Marrec, EBCP, BPI MFBA
Ingénieur en efficacité énergétique du bâtiment
T: +33 6 95 14 42 13
www.julienmarrec.com

DoYouBuzz : www.doyoubuzz.com/julien-marrec_1
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr
LinkedIn (en) : www.linkedin.com/in/julienmarrec


2014-05-28 15:51 GMT+02:00 Nick Caton <ncaton at smithboucher.com>:

>  I’ll take a stab:
>
>
>
> First, watts per square foot is the typical unit of measure for installed
> lighting power in the states.  Installed lighting power is what comes up
> most often in discussions of lighting system efficiencies/gains (in my
> experience).
>
>
>
> Luminous efficacy (Lumens per Watt ) pops up when comparing sources (i.e.
> LED vs. Fluorescent).  When comparing lighting fixtures as a delivery
> method, “delivered” lumens per watt is the preferred metric, which
> additionally takes into account the efficiency of the fixture/housing
> involved.
>
>
>
> Tying these all together:  Watts = 0.09290304 x lux x (square feet) /
> (lumens per watt)
>
>
>
> (yep, I had to google that)
>
>
>
> Ignoring the constants for a moment, W / (m2*lx) looks something like the
> inverse of what I’m used to calling luminous efficacy, so where you might
> describe a lowering of W / (m2 * lx), that would equate to a gain in
> luminous efficacy (lm/W).
>
>
>
> Is that messy enough?
>
>
>
> [image: cid:489575314 at 22072009-0ABB]
>
>
>
> *NICK CATON, P.E.*
>
> SENIOR ENGINEER
>
>
>
> Smith & Boucher Engineers
>
> 25501 west valley parkway, suite 200
>
> olathe, ks 66061
>
> direct 913.344.0036
>
> fax 913.345.0617
>
> www.smithboucher.com
>
>
>
> *From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On
> Behalf Of *Christian Stalberg
> *Sent:* Wednesday, May 28, 2014 5:22 AM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] question regarding lighting efficiency/gains units
> of measurement
>
>
>
> In Europe one sees W/m2-100 lux as a measure of lighting related gains or
> lighting efficiency. What is the equivalent here in the states? I suspect
> it is a messy conversion.
>
>
>
> Thank you in advance.
>
>
>
> Regards,
>
> _
>
> Christian Stalberg
>
> Natural Intelligence, LLC
>
> http://naturalintelligence.us
>
> Tel. 415.531.4610
>
>
>
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