Frederick Williams said:
I know one can dim filament bulbs with triacs (or similar).
I think I know that one used not to be able to dim fluorescent lamps by
the same or similar means.
But can one dim low power lamps _of some kind_ by _some means_?
What is a low power lamp? Is it (at present) a fluorescent lamp?
The questions are prompted by strip lights outside a brach of Sainsburys
that are on all day even in bright sunlight. I would have thought that
lamps could be installed the brightness of which could be controlled (in
an inverse fashion) by the brightness of the incident sunshine. But
would that require the strip lights to be replaced as well?
Please not that my knowledge of things electrical is limited.
Pretty much any commonly used lighting technology (incandescent, fluorescent
(T8, T12, T5, T5HO), compact fluorescent, metal halide, LED, high pressure
sodium, etc.) has means to do dimming. The costliness varies. Sometimes
special 'dimming ballasts' are needed wiht the fixtures, and very often,
special dimmers are needed. And yes, lighting can be controlled based on
daylight (search 'daylight harvesting'). While I do not know what
Sainsburys is (and I am assuming that 'brach' is just a typo for 'branch'),
in a scenario with outdoor fixtures mounted on a building exterior it would
be typical to do less intelligent controls. At least it would be typical in
much of north america. Either photocell control, or a timeclock, or a
combination of photocell and timeclock, might be used. The lights would
just be turned off and on in a more or less 'dusk til dawn' manner.
Astrological timeclocks are available that can accommodate changing
sunrise/sunset times with the seasons, and beyond that they can be
programmed with routines for weekdays, weeknds, holidays, and all sorts of
stuff. And they're not that expensive.
'Low power' may not be a well defined term, maybe 'efficient' is a better
term (depending on what you are actually asing, of course). Certain
technologies are more efficient than others, but if you want lots and lots
of light out of an efficient luminaire, you still need lots of power. All
of the lighting technologies mentioned above are OK for efficiency, except
for incandescent which is not good for efficiency. As rough numbers, I'd
say you can get 70 lumens per Watt to 140 lumens per Watt out of the
efficient technologies above. Fluorescent is probably around 100, and
widely used in normal indoor commercial applications. High pressure sodium
and metal halide are often used outdoors, with efficiencies between say 80
Lumens/W and 140. Incandescent is probably 10-20 lumens per watt. LED
lighting is changing fast. There is a ton of research money and effort
going into LED and it may well be the future of lighting. I don't think it
is king of efficiency yet for bulk lighting, generally speaking. Though for
some people it is the go-to technology. And the marketing hyping it is at
times perhaps a little ... zealous.
There are other newsgroups where you might get a better response on a
question like this. I'm a little rusty on them but
alt.enegineering.electrical might be one, sci.engr.lighting another. I'll
crosspost them in this reply.