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

[Julien Marrec]

Just to be picky, I'll stand my ground. As far as dimensional analysis
goes, 1 lux = 1 lm/m²


That being said, you're right, what comes out of the fixtures doesn't
necessarily end up being useful. As far as lighting retrofits go,
calculations are fine, but you should definitely do a live test in a sample
space before you buy hundreds or thousands of lightbulbs. At least you'll
be able to judge whether you do get the lux level you want as well as
properly assess the quality of the lighting. The CRI is flawed metric (off
topic here)




--
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 17:17 GMT+02:00 Guglielmetti, Robert <
Robert.Guglielmetti at nrel.gov>:

>  "Anyway, for the sake of a dimensional analysis:
> 1 lux = 1 lumen/W. "
>
> Uhm, no it doesn't.
>
> Refreshing as it is to see this discussion trending toward the true
> meaning of lighting efficiency, this is a wiggly target. Too often here in
> the US we see "payback analysis" on lighting efficiency upgrades based
> solely on luminous efficacy, or lumens per watt, or the amount of light
> (luminous flux) that comes outta the lamp. Problem is, we're trying to
> illuminate a space and a task, and the metric here is luminous flux
> density, or lux, which is *lumens per meter squared*.
>
> Lamps (light bulbs) get shoved into light fixtures (or fittings, or
> luminaries, whatever), and they spew light, and the light fixture
> (reflector, lens, whathaveyou) sends some of that light on its way into the
> room, which in turn does more stuff to the light -- it absorbs some, it
> reflects some, and some literally goes out the window. The final answer of
> how much light makes it to the task is expressed in lux, yes. But this
> result is derived by calculating the effect of the *space* on the light
> that made it out of the fixture. This will depend on the shape of the room
> (specifically, its room cavity ratio) and the reflectance of its surfaces,
> primarily. The answer is different for every unique space.
>
> The point is you need to do at least a rudimentary illuminance calculation
> with the new lighting to confirm the ultimate goal (task illuminance) is
> still being met with the new tech. ASSuming it does, then you are able to
> simply relate the new tech to the old in terms of lux/watt, i.e. How much
> "seeing power" you end up with on the desk for a given amount of electrical
> power consumed.
>
> This of course tells you nothing about the overall quality of the visual
> environment, but it's still better than just looking at lamp efficacy.
>
>
>
> Rob Guglielmetti
> NREL Commercial Buildings Research Group
> Golden, CO 80401
> robert.guglielmetti at nrel.gov
>
>
> -----Original Message-----
> *From: *Julien Marrec [julien.marrec at gmail.com]
> *Sent: *Wednesday, May 28, 2014 08:24 AM Mountain Standard Time
> *To: *Nick Caton
> *Cc: *bldg-sim at lists.onebuilding.org
> *Subject: *Re: [Bldg-sim] question regarding lighting efficiency/gains
> units of measurement
>
>    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
>>
>>
>>
>> _______________________________________________
>> Bldg-sim mailing list
>> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
>> To unsubscribe from this mailing list send  a blank message to
>> BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20140528/f8dda082/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 1459 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20140528/f8dda082/attachment.jpg>