Memo Mainstreet Light Levels
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. CITY OF HOPKINS
MEMORANDUM
DATE: March 11, 1993
TO: Mayor and city council
FROM: Lee Gustafson, Public Works Directo~
SUBJECT: Mainstreet Light Levels
A discussion on Mainstreet light levels was scheduled with
council in an attempt to answer some questions that have
arisen over the last year wi th regard to this matter. I
will describe what steps have been taken to analyze the
light levels, and also identify possible alternatives. I
will conclude by giving my opinion and recommendation on
this issue. council may not agree with my recommendation
and decide to take some other action. .
Light Intensity
tf\ Chuck poplar, RLK, met with the sales representative from
our new lights out on Mainstreet one night to check current
light levels. Approximately 35 readings were taken along
the street between 7th and 10th Avenues. After discounting
some readings that were very high due to building lighting,
the average Foot Candles (F.C. ) for various areas were:
0 Middle of street, mid block 1.5 F.C.
0 2 feet behind curb 3.6 F..C.
0 Middle of street, intersection 6.2 F.C.
Attached and listed below are what appears to be data that
was distributed at the December 6, 1990 D.R.C. meeting.
Included in this information was data for light level
comparisons and average light levels for segment 3 and 4.
Average Freeway Lighting 0.6 F.C.
Local Residential Street 0.4-0.9 F.C.
Alley 0.3-0.6 F.C.
Moonlight, Full Moon 0.1-0.2 F.C.
Shopping Center Parking Lot 2.0-5.0 F.C.
Front Door Entrance to Target 15.0 F.C.
Segment 3 Average 1.5 F.C.
Segment 4 Average 1.0 F.C.
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March 11, 1993
Page 2
. Staff unfortunately could not determine from the records
where these average readings for segment 3 and 4 were taken
from. However, we do know from our present readings that
the lowest average for segment 3 with the new lights
(midblock, middle of street) is the same light level reading
average for segment 3 prior to construction. We can
therefore conclude that the preconstruct ion light level
readings were probably taken in the same locations as the
new readings due to the low foot candle readings of each.
We can further conclude that the darkest area of the new
lighting system is as bright as the darkest area of the old
lighting system.
As we are all aware, the old lighting system had low level
lights that created bright spots along the street. It's
quite obvious the average listed for segment 3 in the
attachment did not represent these "bright" areas. I think
it is also safe to say that new lighting system is a more
uniform pattern, and does not have these bright spots that
may have previously given a false indication that the entire
street was brighter.
The last item I want to mention under the light intensity
category is with regard to light color. It is common
knowledge in the lighting industry that a white light coming
. from a mercury vapor or metal halide lamp will appear
brighter than a soft yellow light from a high pressure
sodium lamp even when it gives off less light. Staff feels
that this perception of a whi te light being brighter than
soft yellow light is giving people a false indication that
the preconstruct ion white lights were brighter that the
present lights.
Alternatives
1. Remove refractors (lenses) on the lights. This was
already attempted on the block between 9th and 10th
Avenues. The refractors were removed to see if the
lights would appear brighter. city staff and RLK
concluded there was no difference in appearance.
2, Replace existing 150 watt lamps with 175 watt lamps.
The existing 150 watt high pressure sodium lamps could
be replace with a 175 watt metal halide lamp, socket
and ballast. There unfortunately is not a 175 watt
high pressure sodium lamp available. Technically, a
175 watt metal halide lamp gives off less light than a
150 watt high pressure sodium lamp. However, it may
appear brighter due to its white light source versus
the yellow light source of the existing high pressure
sodium lamps.
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March 11, 1993
Page 3
. 3. Replace all of the single lamp fixtures with double
lamp fixtures. This will approximately double the
..,', light output and you will not have to "scrap" any of
the existing (new) light fixtures. We would have to
determine if the existing wiring will accommodate the
increased load or need to be replaced with larger
cables.
4. Replace the lighting fixtures on the entire system with
250 watt high pressure sodium fixtures. These would be
larger in physical size to accommodate the additional
heat buildup and no longer be in scale with the
existing poles. This would involve scrapping the
inplace fixtures and would most assuredly require all
new wiring.
Conclusion.
In my opinion the existing lights levels on Mainstreet are
more than adequate for their propose. I also believe the
preconstruct ion white lights and the "bright spot" areas are
giving some individuals a false perception that the old
lights were much brighter that the new lights. My
recommendation is therefore to do nothing but enjoy the new
street and everything it. has to offer.
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STREBT LIGHT OESIGN HOPXINSMAINSTREET .
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4IIl~I~TION ~~ ~ND SP~Ct~G DESt~ EL~I
. ampl1n.. Of Llghtin.. 111usn.l.na~lcn l&vels, Irs
Average Freeway lIghting 0.6 Footcl.ndles
MaJo~ Roadway (l.e. Excelsior Blvd.) 1.0 .. 2.0 II
Local Resident1Al Street 0.4 .. 0.9 .
A 11 ey 0.3 - 0.6 II
Moon 11 gh t, fu 1 1 moon 0.1 -0.2 n
Shopping Center ~a~klng Lot 2.0 .. 5..0 ..
r~ont Doo~ Entrance to Target 15.0 II
RIf,.('....tlQnal Sa I 1 r 18 I d 15 - 20 II
Offlce, Internal work1ng area 70 - 150 II
1'AV,irag.'::Qn~';fSegmint::~r.3\:'Qf:ri.iiQP/(lrie'iMa 1"118 er'ei' """''"7.1''''''''''1
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Current numbe~ o~ HIgh/tow fixtures 8, poles 1n Segment #3 · 62
Current number of Hlgh flxtures & polel! in Segment #4 · 43
DE$lGN OPTI~~
Besidee the. cateQorles of contemporary hardware and antique hardware,
and type of mate~lal that the poles are made of ~uch as concrete,
aluminum, steel, etc.; there is the l!ubJ~ct of refu~blshment,
411kePlacement and spacing. See the drawings of the various categorles of
ardWare l!eleetlcn -- pOles and flxturee.
O'Ot ~ ~n #1 -- tDES!GN OPTION IN ESTIMATE .5RJ
Seoment #3: Salvage and replace 25 low level 11 ghts w1 th 35 new
low level lightes. Ref\.lt'bltSh the high level poles/fixtures wlth
total ilxture replacement as needed. It is estimated that 2 out of
3 bases will need re~laeement. Total of 92 poles/fixtures in n8~
deelgn, slIghtly, hl~er' !1lumlnation level .1.6 to 1.7 footcandtes.
Segment *41 R~lJse high level polee/fIxturee on new cases as needed
w1th the same approxlmat. spacIng. Refurbish fIxtures as n..ded.
App~oxlmatelY 30% of the fixtures will need to be replaced.
actIo" .2 --
Segment #3: Remove and salvage atl non-intet'=eetlonal lIghts.
Install new mId-level lIghting ~yetem with 1~ to 18 foot pole
heights. Use salvaged hIgh level poles/fixtures to back-up
replacement/refurb1ehment on the west end of the proJect.
Segment #4: Refurblsh existIng hIgh level sy~tem on newconorete
bames as needed with the same appt"oxlm~te epaclng a.nd the !!!Salve-ged
hardware from segment #3.
QRtlon #3 --
. Segment #3; Same a:s 1n OptIon #1 except all segment #3 fIxtures on
the hlgh level system are replaced wlth new fixtures.
Se~ent #-4: Refurbish existing poles/flxtuz:oes .tthe eam.
app~ox1mate spaclng using the fixtures f~om segment #3 as back~ups. .
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