Subject: Re: Roadway Lighting - MH vs HPS

From: [email-masked] (DaveOesper)
Date: 23 May 1995 19:33:51 -0400

Clay,

Is it possible that with "scotopically enriched" light sources such as
metal halide one runs the risk of increased transient adaptation problems?
 And what about glare?  Is not glare from metal halide worse than HPS for
equivalent luminances?  Even though metal halide has good color rendering,
it often strikes me as being a bit "harsh".  Perhaps that is because often
when metal halide is used, the light levels are too high.  Then there are
the issues of shorter life, lower efficiency, higher cost, color-shift,
greater lumen-depreciation, etc. when compared with HPS.

We astronomers learned a long time ago that if you want to see well at
night, you use light sources that produce little or no light towards the
blue end of the spectrum (minimizing the effect on your rods, e.g.
bleaching of rhodopsin).  Thus, we prefer red LED flashlights.  Now, I'm
not advocating anything that red for roadway lighting, but it seems to me
that HPS and LPS are just fine.  It seems to me that the primary argument
for metal halide is its improved color rendering and "white" appearance. 
But I don't believe that "improved color rendering" is an important
consideration for roadway lighting, especially when you consider that all
motor vehicles come with their own white light sources, called headlights.

David Oesper
Outdoor Lighting Associates, Inc.
Ames, Iowa

---

From: [email-masked] (M. Clay Belcher)
Date: 23 May 1995 14:36:18 -0400

I just wanted to check in again on the great roadway light source debate.  I
would like to hear from those involved in roadway lighting around the U.S. as
to what source you currently prefer and why - Metal Halide or High Pressure
Sodium?  What is actually being installed in your area?  What trend do you
see for the future?

Here in Kansas it's quite a mixed bag.  I am doing an investigation for the
Kansas Department of Transportation to survey what they currently have,
assess how it's performing, and make recommendations for the future.  My task
is limited to the Interstate system.  On the Interstates we have primarily
Metal Halide, high mast lighting, but there's a fair amount of HPS too, as
well as the occasional left-over Mercury Vapor. There is currently no
well-defined policy regarding new installations or future direction (hence
the reason for the study).

At this point we will probably be recommending that all future roadway
lighting be Metal Halide, and that existing HPS be retrofit to MH as ballasts
fail.  This is based on what we see as two emerging areas of consensus.  1)
"Scotopically enriched" light sources (i.e. more power in the blue/green part
of the spectrum) produce better visibility at low light levels.  Thus on an
equal lumen basis (since the lumen is defined by V lambda - photopic vision)
sources like Metal Halide will provide more visibility than High Pressure
Sodium.  2) People simply prefer whiter light as we found in another study
which I hope to present to IESNA in August (regarding a telephone survey of
streetlighting users in Kansas City).

Now of course the first argument could be overturned if the economics were so
greatly in favor of HPS that we could provide equal visibility (taking into
consideration the scotopic effect) with HPS at lower cost than with MH.  In
other words, (taking a purely fictitious example) if it took twice as many
lumens to produce a given level of visibility with HPS as with MH, but it
only cost 40% as much per lumen to install, generate, and maintain the HPS
system, then HPS would still be more economical.  This does not seem to be
the case, but even if it were, we would still have the second argument to
deal with.  How much is people's preference worth, anyway?  (A topic I've
advanced some thoughts on before, as some of you know).

Anyway, I just wanted to see what directions others might be headed on
this issue.

Thanks,

Clay Belcher, PhD, P.E.                 voice:  (913) 864-3434
Associate Professor                     fax:    (913) 864-5099
Architectural Engineering               e-mail: [email-masked]
University of Kansas

---

From: [email-masked] (John Fulton)
Date: Fri, 26 May 1995 10:44:48 GMT

In message <[email-masked]> - [email-masked] (DaveOesper)
 writes:
:>
:>We astronomers learned a long time ago that if you want to see well at
:>night, you use light sources that produce little or no light towards the
:>blue end of the spectrum (minimizing the effect on your rods, e.g.
:>bleaching of rhodopsin).  Thus, we prefer red LED flashlights.  Now, I'm
:>not advocating anything that red for roadway lighting, but it seems to me
:>that HPS and LPS are just fine. 

It seems to me that the high pressure sodium lamps are better for road 
lighting because the source of light is smaller, and is thus easier to design 
a luminaire that has good light distribution.

The low pressure sodium lamps although they preduce more light, it is much 
harder to get this light where it is needed, and keep low glare for good 
visual ability.  In times past these low pressure lamps were in common use, 
but once it was realised that better road lighting can be got from high 
pressure lamps, they became the lamp of choice for most road lightihg schemes 
in New Zealand.

Mercury vapour lamps are used in some urban areas where shopping areas 
require better colour rendering than is possible with sodium lamps.

Regards to you all

// John ER Fulton - Ngaio - Wellington - NEW ZEALAND
// Phone +64 4 479 2043  -  FAX  - +64 4 479 2043

---

From: [email-masked] (Philip Decker)
Date: Fri, 26 May 1995 16:10:52 GMT

I hope all of you involved in outdoor lighting are
supporting members of the International Dark-Sky
Association (IDA).  Otherwise, the day will come
when there are no urban residents who remember
seeing the stars.

PJD

---

From: [email-masked] (David Clarke)
Date: 27 May 1995 02:55:28 GMT

>Sodium?  What is actually being installed in your area?  What trend do you

My personal preference has to be Metal Halide.

Here in Calgary (Alberta, Canada) most roadway lighting is HPS.  A few MH 
units have been installed, presumably during relamping and as a test, and the
results are a dramatic improvement in the quality of the roadway lighting - and
hence improved roadway safety.  My opinion is that the HPS units can't be changed
out fast enough.

I prefer MH over HPS because: MH enables one to see details easily;  MH doesn't
"wash out" the illumination of the roadway by ones vehicle headlights (as does
HPS);  and MH provides a more natural spectral output (man's eyes are not that 
sensitive to that dull orange light !).

My current client has expressed a preference to MH over HPS for all lighting in their
new plant.  They are not alone in their preference.

As an aside; there are still a few old mercury lights in the city - I just love them.