Alternatives to HPS

[Jan Hollan <jhollan@amper....muni.cz>]

> A friend sent me the question below. I would like to get your  opinion.
>
> I'm looking for a good, night friendly  alternative to High Pressure Sodium
> lights. The local electric co-op is willing  to offer to its members an
> alternative to the current HPS lights they offer if  the maintenance for the
> alternative lights is relatively the same as the HPS  lights. Any thoughts or
> suggestions?

Hi Cindy,

In my opinion, HPS bulbs can be regarded as one of the least polluting
light sources, if they are inside fully shielded fixtures (no light
horizontally and upwards), esp. those ones, which also avoid light
emissions onto targets which need not to be illuminated.

For many purposes, HPS are clearly the best ones. No other discharge
sources can beat them as regards lamp life.  Still, in some cases, less
seriously polluting (due to spectral composition or reduced light output)
sources can be cost-effective, even when health and wildlife impacts are
not included:

1) LPS

Much less serious pollution would be produced by Low Pressure Sodium
bulbs (lengthy tubes, straight or U-shaped), _provided_ they are inside
similarly well-directing fixtures (what is in some cases not easy, due to
the size of LPS). LPS emits still less shortwave light, which is more
damaging in most respect. And emits more light per watt, reducing power
consumption (and fossil carbon emissions) for the same lighting task. For
road or footpath lighting, where monochromatic (similar to colourless
photos or TV) vision suffices, they can be a better alternative to HPS. A
18W LPS bulb exits, whereas for HPS the smallest kind is 35W (still, many
lighting ``experts'' don't know it and consider 50W to be the least strong
source) -- it can be a good choice when not much light is needed.

LPS have a disadvantage, that they cannot be dimmed (HPS are easy to dim,
to one third or even one fourth of light output). LPS are more vulnerable
to overvoltage, exhibiting a good life expectancy (up to 16000 h) just
there, where voltage is stabilised. In such environments, best HPS have
just 1.5 times longer life expectancy, 24000 h. LPS are less obtrusive if
they are in your field of view (e.g., you are looking up), as they are
long and have much less luminance than HPS (for the same amount of light,
LPS appear much less glaring).

Lack of colour vision is in fact a prerequisite for minimised health
risks:  absence of light with wavelengths below 580 nanometres makes sure
that even considerable light intensities (like 30 lx) don't compromise
nighttime melatonin production.


2) Fluorescent

Linear or U-shaped fluorescent tubes share with the LPS the advantage of
being less glaring than HPS, and the disadvantage of needing large
fixtures. Their disadvantage is shorter life, compensated however by lower
cost.

For low illuminances, below 1 lx (or below 0.2 lx if the target is snow),
they may have an advantage of enhancing nighttime vision, having a larger
blue component. Metal halide bulbs, which are white too, are often too
strong already. Fluorescent sources are available from 5 W on.

3) Incandescent

If the lights can be activated just on demand, for say half an hour each
night, and 3 lx or less is enough, halogen incandescent bulbs with good
possibility of achieving excellent light distribution (like with car short
lights) may be the best choice: lamp life of ten years and minimised
power consumption.

4) LEDs

for narrow paths and 0.1 lx illumination (like that offered by full moon)
they can be an ideal choice (more on it in my old posting,
   Linkname: Re: LED streetlamps
        URL: http://amper.ped.muni.cz/jenik/letters/public/msg00189.html).
Unfortunately, I'm aware of no product like that being on the market.


So, these are the four alternatives. To perform better than HPS, the
primary criterion (no light horizontally and minimised emissions at
directions 15 degrees from horizontal and above) has to be fulfilled of
course.

What I have explicitly to warn from, is replacing HPS by MH or any other
``white'' bulbs, if the illumination remains strong (over 3 lx). Such
strong white light makes much more harm than the orange HPS light. Yellow
or orange is adequate for the evening and night (and should be employed
for interior lighting as well), even if current business promotes white
light a lot nowadays.

with best regards,
 jenik