Fixture transmission of light?
Sarah Austin
fixture lets out.
Are there any standards for measurements of the percentage of light that
T8 tubes, for example, put out, versus how much escapes from the bottom of
the fixture diffuser?
Like a transmissivity percentage standard or something?
I'm looking at fixtures like this one:
http://www.lampsusa.com/index.asp?PageAction=VIEWPROD&ProdID=66260
and it says it has a clear prism diffuser. So that's the best you can do
with those?
But what about reflecting the light that comes out the top of the tubes,
downward, like I mentioned before with the polished reflectors?
It seems like the overall percentage of light output would be a function
of how much of the top light was reflected downwards, and the
transmissivity of the diffuser.
I see the above one is "Energy Star" rated, but am not sure what that says
about it.
TKM
"Sarah Austin" <SAu...@pndfnospam.com> wrote in message
news:Xns9CB3C4FEF515Sn...@216.196.97.142...
It's all standard stuff. All of those data are part of a standard luminaire
photometric report.
There are are about 50 such reports in the current Illuminating Engineering
Society Handbook for common luminaire types that list (1) luminaire
efficiency, (2) coefficient of utilization (the amount of light that reaches
a given work plane divided by the light output of the lamp) (3) distribution
of light from the luminaire as a plotted curve (4) % directed down and %
directed up from the luminaire.
The IES Handbook is not on line (as far as i know), but is available in most
technical libraries. The current version is the 9th. Edition. See Chapter
9.
Terry McGowan
boxman
You're getting into the esoterics of actual fixture design without
considering the application criteria of the lamp in it's end use.
By using highly reflective material above the lamp, you can get more
light out. For example, a well known reflector material supplier to the
lighting industry is ALANOD. Their MIRO brand material has a
reflectivity of 95% and they have a silver material that can reach 98%.
So in theory when you bounce the top light off those surfaces you
could send 98% of that back out of the fixture. You can also buy really
expensive diffuse white coatings and materials that have close to the
same reflectivity of the MIRO material. The problem becomes where you
put the light that you reflected out and how you apply that fixture to
the space you are lighting. If you use a miro material and shove all
the light directly below the fixture, then trying to light a large area
with those lamps would be a difficult task and you would end up using
way more fixtures than a lamp that has diffused the light over a large
angle.
A lot of fixture manufacturers publish the measured data of their lamps
for usage by lighting designers in layout calcualations. In those files
you will find the total efficiency of the lamp as measured by the lab.
You could, if you wanted to use this number to compare fixtures for
total efficiency. For example this lamp
http://www.lightolier.com/products/index.jsp?CATREL_ID=28464&BLK=N&CAT_ID=27440
has a fixture efficiency of 85% according to their data on the website
which is quite good . (The data is in the form of an IES file which
requires viewing software to analyze). This lamp is without a lens. By
comparison, this lamp with a lens
http://www.lightolier.com/products/index.jsp?CATREL_ID=26320&BLK=N&CAT_ID=24939
Lists the efficiency at 65% based on the measured data. Any time you
add a lens, you are probably losing at least 4% of the light and maybe
significantly more depending on the material quality and geometrical
construction of the lens.
However just comparing total efficiency doesn't give you the whole
story, as you also have to look at the angular beam output from the lamp
and how that beam fits into the space you are trying to light. If you
have an 85% efficient lamp that has narrow beams and you are trying to
light a large area, you may end up using more fixtures (and thus more
energy) than using a 65% efficient lamp that has a wider beam. The two
are linked and you can't judge on just one criteria when looking at a
given situation.
TKM
"boxman" <box...@voyager.net> wrote in message news:hcevt8$dfv$1...@aioe.org...
Boxman is right. If you're interested in knowing more, download the
Advanced Lighting Guidelines. The 2003 version is now free to download (you
just have to register) and it is very clearly written. Look at Chapter 7,
"Luminaires and Light Distribution". The New Buildings Institute is the
source. Go to:
http://www.newbuildings.org/ALGfiles/PDFSet.htm
Terry McGowan
Sarah Austin
> _ID=24939 Lists the efficiency at 65% based on the measured data.
> Any time you add a lens, you are probably losing at least 4% of the
> light and maybe significantly more depending on the material quality
> and geometrical construction of the lens.
>
> However just comparing total efficiency doesn't give you the whole
> story, as you also have to look at the angular beam output from the
> lamp and how that beam fits into the space you are trying to light.
> If you have an 85% efficient lamp that has narrow beams and you are
> trying to light a large area, you may end up using more fixtures (and
> thus more energy) than using a 65% efficient lamp that has a wider
> beam. The two are linked and you can't judge on just one criteria
> when looking at a given situation.
Thanks for the info! :-)
Sarah Austin
> Boxman is right. If you're interested in knowing more, download the
> Advanced Lighting Guidelines. The 2003 version is now free to
> download (you just have to register) and it is very clearly written.
> Look at Chapter 7, "Luminaires and Light Distribution". The New
> Buildings Institute is the source. Go to:
> http://www.newbuildings.org/ALGfiles/PDFSet.htm
>
> Terry McGowan
Thanks both of you! :-)