Incandescent efficiency

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Oops... Should be:

Nope.

At any point where you reduce the voltage the power output will be less
than it was before you reduced it.

Sure! There's no free lunch. The point is, if you want to prolong the life of the bulb, operate it at a reduced voltage (e.g., the bulbs in the house are rated at 130V. We buy "a size larger" than we need -- 100W when we want

75W, etc. -- and I don't think we've replaced more than two in the many years we've been here).

Sorry, that wasn't my intent. I was, instead, pointing out that reducing the voltage works in my favor in terms of "generating heat" (inefficiency)

You're saying the (visible) "light" energy output will contribute to heating as much as the infrared energy output?

I can get maximum heat out of them by operating them off the 220 line instead of 110! :> Lamp life will suffer, though! :>

The points I intended to make here are:

- light bulbs are *almost* as good as resistors in terms of converting electricity to heat (i.e., they are very inefficient at generating *light*)

- as you decrease the operating voltage on a lamp, you increase its life expectancy

- as you decrease the operating voltage on a lamp, you decrease its efficiency and, thus, the relative amount of heat derived from the power source

- light bulbs are cheap. You can add extra light bulbs to make up for any net loss in total power dissipated by adding still more light bulbs (this is a good thing as it also lets you convert the heat source from a point source to a distributed source)

If someone had commented that, for example, resistance

*doubles* as you operate the bulb "cooler" (lower V), then this would have been a double whammy -- power decreasing by an inverse square relationship (with V) *and* further decreasing by an inverse relationship (with the increased R).

It also helps me to understand the relative merits of, for example, large lamps under the trees vs. smaller lamps (e.g., XMAS lites) strung *through* the trees.

Earlier on, I was about to suggest stringing two bulbs in series when I saw that you'd already thought of that as an option. But since the point has been raised again more than once, let me put in my 2 cents worth by saying that I also think it's the best compromise between initial investment (more bulbs) and simplicity plus long term economy (/much/ longer bulb life).

Regarding efficiency, I think it's a minor issue. Incandescents are already about 90% efficient at producing heat even at their nominal voltage. I've often observed in practice that they still radiate a considerable amount of light at half-voltage and are therefore still not 100% efficient as heating elements. So the gain in heating efficiency will be only a few per cent at half the nominal voltage.

Some of it must, since some part of visible light striking dark foliage will be converted to heat. Also, IR will shine out and away from the target as easily as visible light. You might get some gains by using a reflector on each lamp to make sure that all radiation, of whatever color, moves upward into the foliage.

--
John

Yes. When I first had to face the dilemma of "how do you keep the trees from dying", I noticed all the neighbors had a combination of covering the trees and/or putting lights under/in them.

Of course, I realized the lights were just acting like heaters. So, I figured I could "go one better" and put some really big resistors under the trees, etc.

Then, when I researched the bulb (in)efficiency, it was silly to spend any time/money on any other approach as the lamps *were* "resistors" -- for all practical purposes. And, you can buy outdoor lamps whereas putting any sizable resistor outdoors would require some special handling (liability issues, etc.)

Now that the trees are *way* too big to cover (the smallest requires a "sheet" made of six California King bedsheets stitched together -- the sheer weight of the sheet isn't good for the tree, either), the bulbs are becoming more of an issue.

Since the fruit comes ripe this time of year, burying the tree isn't an option! :>

Agreed. I only pointed it out to nail down that niggling detail.

The *real* solution is to move someplace *warmer*! (or, colder and eat apples instead!)

On a sunny day (Thu, 21 Jan 2010 13:43:15 -0700) it happened D Yuniskis wrote in :

How about some of those big heat guns (on oil I think) like they use in garages blowing up towards the tree top? The CO2 will help the trees too.

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As I recall, there's a gotcha in there somewhere about that it costs you
more dollars per lumen if you use 130V lamps on 120V, but what does
using 130V lamps on 120V have to do with keeping trees from freezing?

After all, what you're looking for is I²R.

oman

s

on

The factor of ten difference in resistance doesn't make the filament lamp a constant current device; it looks more like one than a simple resistor, but as a pedagogic device this is a bust.

And if you could find any "climate crap" in the rest of the post you've got to be confusing basic physics (radiated power increasing as the fourth power of temperature) with the discussions of the greenhouse effect that sometimes include this simple fact.

-- Bill Sloman, Nijmegen

loman

is

s on

.

How does pointing out that a filament lamp isn't a constant current device become some kind of "lame insult"?

I know that John Larkin doesn't like it when he posts similarly inane comments, but that doesn't make a simple factual observations any kind of insult, lame or otherwise.

It's a fair measure of John's emotional development that he needs to sooth his injured pride by posting his own brand of lame insult.

-- Bill Sloman, Nijmegen

[snip]

Radiation from the bulbs will heat the surfaces that the radiation strikes. If the objet is to warm air and generate convection, you might want to try the following:

Place a 'chimmny' around each bulb. A large tin can with the top cut off and some holes around the bottom. The light warme the can, the can warms the air and the air rises into the trees. Shining the lights on the trees may not be nearly as efficient at generating air circulation.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
If life was fair, Elvis would be alive and all the impersonators
would be dead. -- Johnny Carson

Some numbers from a handbook:

life is inverse on volts^13

lumens go as volts^3.4

watts go as volts^1.54

lumens/watt go as volts^1.84

John

Which is why dropping 5-10% of line voltage on hard to install awkward lights can be enormously beneficial in reduced maintainence costs. Some sources claim an optimistic higher power dependence V^-16 or so.

I reckon doubling the lifetime of his bulbs would be worthwhile and would not represent an enormous hit in delivered. Just 8% less if he put the 5% ballast resistors in a waterproof box under one of the trees.

I think this might be what the OP actually wants but with the sums done for the specific case of two bulbs in series vs two bulbs in parallel. I have used power ~ V^1.6 as it makes the numbers easier.

2 bulbs in parallel each 100W nominal on 100V supply each draw 1A (total current drawn from supply 2A) power delivered = 200W total 2 bulbs 100W nominal in series but now on 50V supply draw only 0.66A and each one consumes 100*(1/2)^1.6 = 33W drawing 0.66A so total = 66W

That means with the two bulbs in series configured light strings you need to use three times as many bulbs on the trees. I suspect the capital cost outweights any possible gain from lower repair bills.

But in this case he isn't interested in the lumens - they are wasted light. Indeed as someone else has suggested putting the lights in tin cans so all light is converted to heat and IR might be beneficial.

I suggested silver dipping them or flame proof paint on the surface.

Regards, Martin Brown

On a sunny day (Thu, 21 Jan 2010 15:56:29 -0800 (PST)) it happened Bill Sloman wrote in :

Well, I have worked with equipment that used that constant current feature for AC voltage stabilisation, was in a big OIL company actually, controlling the biggest variacs you have ever seen.

You are a anti warming fanatic, those want to kill incandescent bulbs, so anything you say about it will probably be politically motivated, some agenda.

On a sunny day (Thu, 21 Jan 2010 16:02:48 -0800 (PST)) it happened Bill Sloman wrote in :

Emotional development seems to be your hanger no?

John posts interesting new designs and ideas. Do you even have a multimeter? I mean one where the battery still works?

loman

Sure. It is mostly used to check how far gone other batteries are, but if I ever get my current project to the point where I build a real electronic circuit, it will be measuring the DC output from the demodulators.

-- Bill Sloman, Nijmegen

loman

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e for AC

biggest variacs you

agenda.

Don't be silly. The nearest I get to "killing incandescent bulbs" is replacing standard 60W spots with the 42W equivalents built with a tungsten halogen insert; not only are they more efficient, but they also last twice as long. I don't really see the sense in replacing tungsten filament lamps in application where they they aren't turned on for very long - compact fluorescent lamps don't last too long in that sort of application, which probably means that our society would put out more CO2 from building the lamp than it would save during its (shortened) lifetime.

Find a political agenda in that.

-- Bill Sloman, Nijmegen

On a sunny day (Fri, 22 Jan 2010 04:29:04 -0800 (PST)) it happened Bill Sloman wrote in :

Do not tungsten bulbs put out more UV? Dangerous for your skin?

We will have to wait and see what other bad things you post about those lovely incandescents :-)

oman

l S=3D

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Tungsten-halogen not only runs hotter than conventional filament lamps, but also rely on a silica capsule to keep the air out, which is transparent out to about 200nm.

Sadly for your alarmist warning, the tungsten halogen bulbs that I use have a soft soda glass outer casing which absorbs most of the danerous UV (such as there is of it) so they are no more dangerous than conventional filament bulbs, which is to say not even as dangerous as sun-light in the Netherlands (which has to travel an appreciably longer path to get to me than summer sun in Australia, and consequently contains very little skin-damaging UV - much less than I soaked up as a child, when it actually matters).

ovely incandescents :-)

Pity about your ill-informed imagination.

-- Bill Sloman, Nijmegen

in

The big advantage of 10% buck/boost transformers is that you get the = voltage=20 change for about 10% of the iron and copper cost/weight. It would be = more=20 like a 300 W transformer.