Fash wrote:

A couple of points:

Low voltage halogens are ~twice as efficient as mains voltage, so start
there.

Hold on, there is more to it. The lightbulbs themselves, if 12v, are a
bit more efficient, but the way theyre almost always used is
murderously inefficient. So in practice 12v halogen lights are on
average much bigger energy guzzlers than GLS.

So dont start there at all, its the worst of all options. Halogens are
also the highest fire risk of all lighting types, and have other issues
too.


Mains halogen ~10 lumens/W
Incandescent ~13 lumens/W
Low voltage halogen ~20 lumens/W
High efficiency low voltage halogen ~25 lumens/W
Compact fluorescent ~40-60 lumens/W (depends on colour rendering
properties)
Tube fluorescent ~60-70 lumens/W (depends on colour again)

If this is translated into cost per annum people get a shock when they
see those halogen costs, the highest by far. In short halogen
downlighting will cost thousands to run. I wish that were an
exaggeration.


The colour of white light is measured in terms of a CRI (Colour
Rendering Index) where 100 represents the colour of a pure tungsten
filament. The CRI is a measure of the ability of a light source to
accurately represent colour. For example sodium lamps have very high
efficiency (approaching 200 lumens/W) but diabolical CRI which is why
everything appears as shades of orange. Halogens have very good CRI so
the colours of objects appear to be the same as in daylight.
Fluorescents vary greatly depending on manufacturer, price and
efficiency, generally better CRI means lower efficiency.

This makes halogens a good choice for kitchens and places where you
want colours to be vibrant i.e. red peppers to be red rather than
orange.

no it doesnt. Many CFL and linear fl also have good CCT and high CRI,
and win by miles in other respects.


re LEDs, theyre still gimmick lighting at this time. Maybe one day, but
certainly not today, not for normal household uses.


NT