Luminance meter

Dear all
I'm looking into buying a Luminance meter in order to carry out some light
measurements in urban open spaces. The ideia is to have some sort of
reference values in key open spaces of different configuration and surface
materials, that we can use as a basis to understand what the brightness
values we get in our simulated scenes actually mean in the real world.

I've been looking at Minolta LS100
(http://www.tequipment.net/MinoltaLS100.asp
<http://www.tequipment.net/MinoltaLS100.asp> ) with very greedy eyes. But
the price is quite high (more than £2,000 and as high as £3,000 in some
websites). I was wondering if this is the sort of price I should expect to
pay for a good meter or if there are others that will do the same job and
are less pricey? Would anyone suggest any other instruments?

Thanks in advance.
Raquel

Raquel Viula
Foster and Partners
Riverside Three
22 Hester Road
London, SW11 4AN

Raquel,

We bought an LS100 a year ago. At the time of choosing, there didn't seem to be much in the way of competition, but that may have changed. Regarding your intended use, there are a whole raft of confounding factors that can (and invariably do) make comparison of measured and modelled values in an urban setting highly problematic. I addressed some of these issues in a recent LR&T paper:

Verification of program accuracy for illuminance modelling: assumptions, methodology and an examination of conflicting findings
Lighting Research and Technology, Volume 36, Number 3, 1 September 2004, pp. 217-242.

Abstract:
This paper examines the role of assumptions commonly made in validation studies for lighting simulation programs and quantifies the sensitivity of results to uncertainties in key model parameters such as sky conditions and surface reflectivity. Actually occurring overcast skies are often taken to approximate the CIE standard overcast sky for the purpose of comparing predictions against measurements in real buildings. The validity of this assumption is tested against measurements of the sky luminance distribution for real skies. Illuminance predictions are particularly sensitive to the assigned reflectance of surfaces when the direct component of illumination is small. A number of confounding factors that can lead to imprecise estimates of surface reflectivity for building facades are identified and a methodology to minimize their effect is proposed. This study reveals that commonly made assumptions with respect to sky conditions and moderate imprecision in model parameters can lead to erroneous assessments of program accuracy. The degree to which existing validation findings can be extrapolated to very different application scenarios is discussed in the context of reported conflicting assessments of program accuracy.

Although concerned mainly with illuminance predictions, much of the discussion applies also to luminance. Contact me directly if you require a copy of this paper and don't have access to the journal.

-John

Radiance 2006 Scientific Workshop, 13-14 (Wed-Thu) September, De Montfort University, Leicester, UK.
http://www.iesd.dmu.ac.uk/~jm/radiance2006work.html

···

-----------------------------------------------
Dr. John Mardaljevic
Senior Research Fellow
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972
+44 (0) 116 257 7981 (fax)

[email protected]
http://www.iesd.dmu.ac.uk/~jm

Photographic spot meters for luminance measurements, and photographic
incident light meters for illuminance measurements, though it does
take some calculation to go from exposure values to luminance and
illuminance values. Used photographic meters cost much less than a
new LS100, and there are many good ones available.

See <http://www.vsg.cape.com/~pbaum/meter1.htm>. If you really need
lots of specific info about light meters, see *The Hand Exposure Meter
Book*, by Hirschfeld, et al. (not seen, but I know one of the authors by reputation).

Randolph

···

On Mon, Jun 26, 2006 at 12:01:30PM +0100, Raquel Viula wrote:

Dear all
I'm looking into buying a Luminance meter in order to carry out some light
measurements in urban open spaces. The ideia is to have some sort of
reference values in key open spaces of different configuration and surface
materials, that we can use as a basis to understand what the brightness
values we get in our simulated scenes actually mean in the real world.

Here is a link to the Sekonic L-558C Dualmaster - Digital Incident, Spot and Flash Light Meter that includes a 1 degree reflected light spotmeter and It offers foot-candle, lux, foot-lambert and cd/m2 measuring modes.

http://www.sekonic.com/products/products.asp?ID=5

Here is a sample price from BH Photo - $639 new.

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=300412&is=REG&addedTroughType=categoryNavigation

maybe this is a useful alternative?

kirk

···

------------------------------

Kirk L. Thibault, Ph.D.
[email protected]

p. 215.271.7720
f. 215.271.7740
c. 267.918.6908

skype. kirkthibault

On Jun 26, 2006, at 7:01 AM, Raquel Viula wrote:

Dear all
I'm looking into buying a Luminance meter in order to carry out some light measurements in urban open spaces. The ideia is to have some sort of reference values in key open spaces of different configuration and surface materials, that we can use as a basis to understand what the brightness values we get in our simulated scenes actually mean in the real world.

I've been looking at Minolta LS100 (http://www.tequipment.net/MinoltaLS100.asp) with very greedy eyes. But the price is quite high (more than £2,000 and as high as £3,000 in some websites). I was wondering if this is the sort of price I should expect to pay for a good meter or if there are others that will do the same job and are less pricey? Would anyone suggest any other instruments?

Thanks in advance.
Raquel

Raquel Viula
Foster and Partners
Riverside Three
22 Hester Road
London, SW11 4AN

www.fosterandpartners.com

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I was wondering is there another windows based program that packages
RADIANCE as a lighting analysis tool.

Best
Charlie Portelli