In article ,
krw wrote:
On Thu, 17 Dec 2009 17:26:31 -0600,
(Robert Bonomi) wrote:
In article ,
krw wrote:
[[ sneck ]]
Much longer, yes. Bulb life is a function of something like the 16th
power of service voltage.
Eleventh power. not 16th. grin
a 5% decrease in voltage equates to an over 70% increase in bulb life.
I've heard everything in between too. I haven't seen any definitive
reference, though.
I have. grin The '11th power' figure comes from a college dorm-mate.
He'd interned with GE in their lighting manufacturing operation. And his
masters thesis was on the subject.
AFOAF? ;-)
Try reading again.
I knew the guy, personally. His masters thesis was
on the subject of optimizing lightbulb construction. I actually read the
whole thing -- before submission, in fact, as he wanted my editorial help,
and knew I could also follow the math.
The gathered experimental data fit a simple 11th order curve (with an error
under 5 parts in 10,000), over a range of more than three orders of magnitude,
in bulb life. i.e., of the form ax^11+k, no other elements.
Doesn't much matter which, the point stands.
Actually, it does, when you're justifying running some lighting circuits
off a (slight
step-down auto-transformer. Accurate predictions of
results _do_ lead to repeat business.
It's still not saving money, unless there
is a cost associated with replacement in addition to the bulb cost.
Depends on what you're measuring. grin
"Per lumen of light output", the de-rated bulb is more expensive to
operate.
Generally light bulbs are used to make light.
yup. But many people (erroneously!) consider _only_ the cost 'per hour of
operation', in which case the de-rated bulb is _always_ less expensive _per_
_hour_ than the one operated as rated.
If the de-rated output is 'adequate', and you're just looking at the cost of
operating "a bulb", the 130V bulb does save a little (circa 10%) operating
money. Plus a little more for the reduced replacement frequency. The only
_real_ advantage comes if the bulb is located somewhere where it is _hard_
to change -- i.e., with a significant 'labor' cost involved in performing
the replacement.
If can get by with less light, use a lower wattage bulb.
With standard light-bulbs, that may _not_ be an option. Try and find an
off-the-shelf (i.e., that you can by in a grocery, hardware, or home-
improvement store) 'lower wattage bulb' with, say 10% less lumens than a
standard 100 watt 120V one. Quite simply, they don't exist.
You assume *exact* illumination is required.
No I don't. For many kinds of environments there is a _minimum_ recommended
level of illumination for the task(s) done there. (more below)
For standard incandescent bulbs, going up 'one standard wattage' results
in about 50% more light output. Note; at the _same_ service life, light
output _does_ correlate linearly with power consumption. One gets 50% more
light from a 75 watt bulb, vs a 60 watt one, because of design differences
that result in a 25% _lower_ life expectancy for the 75 watt bulb.
Like most physiological
things, vision is logarithmic. There really isn't that much
difference between a 75W bulb and a 100W bulb that a 100W 130V bulb
would squeeze between.
_That_ depends on the environment, and the situation. In business settings
you have to have certain minimums to keep OSHA inspectors, insurers, etc.
happy. With built-in fixtures, you can't change the source to work-
surface distance, so all you _can_ play with is the light output of the
bulb. 'Subjective' perception, or not, that circa 50% range between
adjacent standard bulb ratings _is_ enough that the 'legal' requirement
can preclude using the next lower standard rating, but still allow the
use of a, say, de-rated 130V bulb.
is a PITA to get to, spend the money. It really is that simple.
On -that-, we are in complete agreement.
I may do that for my great room can lights and ceiling fans. The fans
only take a 10' ladder to get to, but the can lights are going to be a
real PITA. I don't use them because I really don't want to get up
there until I have to paint the ceiling. ;-)
If they're regular bulbs, in flush-mount ceiling fixtures, there is a
'grabber' pole that makes that height pretty much a non-issue. grin
Now a _cord-supported_ can hanging 30+ ft above the nearest floor surface
(and 6-8 ft below the ceiling) is an entirely different story. Can't use
the grabber pole -- the fixture isn't 'stable' enough to grab the bulb,
Have to bring in the portable man lift, move furniture out of the way for
_that_, etc. it can easily take an hour or more, all told, to change a
=single= light bulb. (One can probably, however, change at least 5-6 bulbs
in the same room in 90 minutes total.