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

[Nick Caton]

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?

[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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