Light bulbs produce heat ~ from lumens or wattage, or ?

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Old 05-12-06, 08:20 PM
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Light bulbs produce heat ~ from lumens or wattage, or ?

I have always known the CFL's produce likes heat that regular incandescent bulbs of the same wattage equivelency (based on light output). But just the other day, something dawned on me:

I got thinking. If a CFL truly puts out the equivelent of light as an incandescent (say you are comparing a 60 watt bulb incandescent to a 13-15 watt 60 watt equivelent CFL)...then why the heck isn't as much heat generated?

And conversely...if you were to instead factor in the wattage applied, instead of the lumens factor...then one could guess that the CFL would produce only 1/4 the heat (but that isn't the case; read on).

But guess what? I experimented and found the results did not answer my question. Instead the results seem mysterious. Here is what I did, and here are the numbers:

I put a probe thermometer inside a jelly jar fixture with a 60 watt incandescent. I got 230 degrees (viewed through the glass while globe is on). I put in a 60 watt equivelent CFL (13-15actual watt consumption) and the temp inside was 140. I did repeat tests. I also put in a 40 watt appliance bulb and got 212.

So can you explain the temp readings?
 
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Old 05-12-06, 08:37 PM
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Dave;

sure i can try to explain in layman terms if i can

the indentscent bulbs do have filment that generated heat for light.

to get good light level the filment have to get white hot which it will give out heat aka like heating element on the stove burner

for CFL [ compact flourscent light ] they work completly diffrent princple than indentscent due the indentscent do have filment and yes CFL and reguar floursecent do have filment as well but it work in diffrent way they use diffrent gas filled bulb and use the " arc " to jump across the gas filled bulb and the arc hit the white powder coating which it will glow like white or few other color as well.

let you know that the CFL dont start too well in cold weather if you noticed expect few electronic verison can start at low as -20 degress F. but not very bright until it get warm up once it warm up it will proudce nice light level what it design and the other benfits is that CFL have long burning time they go much as 10,000 or more hours before they burn out.

[ some CFL can be dimmable but most are not depending on bulb and ballast design ]

Merci, Marc

if want more question feel free to ask us
 
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Old 05-12-06, 09:03 PM
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It's partly efficiency: incandescents wast more energy by generating heat than the CFL.
 
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Old 05-12-06, 09:08 PM
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Just another layman's thought, but doesn't the incandescent also have a resistance that produces heat?
 
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Old 05-12-06, 09:23 PM
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All types of light bulbs are rated on several factors. One of these is wattage, which is strictly a measure of electric consumption. A 60 watt bulb consumes 60 watts of energy. A 15 watt bulb consumes 15 watts. Now, light bulbs have the interesting property that in one way or another the passage of electric current through the filament, through the gas tube, etc. produces light output as well as heat. A 1000 watt hair dryer consumes 1000 watts, gets hot, but produces no light output. An electric motor consumes watts, prodces some wasted heat, and also does work ( rotation ). You notice that a motor using 1000 watts is no where near as hot as a 1000 watt bulb, so we can see there are different ratios of heat vs. watts for various devices.


As you have already realized, a very rough light output comparison is that a fluorescent bulb produces the approximate light output ( lumens, candlepower) as an incandescent of 4 times the wattage. The gas tubes are very efficient at producing light with not a lot of heat. The ballast also consumes energy and produces heat.


So, watts is a measure of electricity, and has some relation to heat, but is not related to light output. Light output is related to the physical charisteristics of the material: filaments ( tungsten, halogen), ionized gas( metal halide, mercury vapor. high or low pessure sodium), or even the new light emitting diodes. You may have noticed that municipalities almost everywhere are changing out the lamps in traffic signals to LED. The energy savings on an annual basis is enourmous.
 
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Old 05-13-06, 07:41 AM
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Originally Posted by DaVeBoy
I put a probe thermometer inside a jelly jar fixture with a 60 watt incandescent. I got 230 degrees (viewed through the glass while globe is on). I put in a 60 watt equivelent CFL (13-15actual watt consumption) and the temp inside was 140. I did repeat tests. I also put in a 40 watt appliance bulb and got 212.
Heat transfer is not linear. This means that the hotter it is inside the jar relative to the ambient room temperature, the faster the jar will cool off. The jar at 230 degrees is losing much more heat to the surrounding room than the 140 degree jar is. Therefore, the incandescent bulb is not only heating the jar to 230, but also releasing a lot of heat into the room. The CF bulb is only heating the jar to 140 and releasing much less heat into the room. This is where the hidden "four times" as much heat is.
 

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Old 05-13-06, 08:52 AM
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It is simple. Watts does not equal temperature. You can have 25 watts and depending on what you do with it depends on the heat. My 25 watt soldering iron will get very hot compared to a 25 watt wall adapter for a radio.
 
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Old 05-13-06, 05:52 PM
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Originally Posted by mitch17
It's partly efficiency: incandescents wast more energy by generating heat than the CFL.
Yes, I know. But you haven't answered WHY the difference...and why the specific temperature difference. I am enjoying reading the answers. Time to read on.
 
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Old 05-13-06, 05:55 PM
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Originally Posted by the_tow_guy
Just another layman's thought, but doesn't the incandescent also have a resistance that produces heat?
Good point. Maybe light has nothing in and of itself to do with heat?...and it's maybe really a frictional thing caused by resistance? Hmmmm. Now I'm thinking about fusion in the sun. Hmmm. My brain may explode from all this pondering.
 
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Old 05-13-06, 05:59 PM
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Originally Posted by 594tough
All types of light bulbs are rated on several factors. One of these is wattage, which is strictly a measure of electric consumption. A 60 watt bulb consumes 60 watts of energy. A 15 watt bulb consumes 15 watts. Now, light bulbs have the interesting property that in one way or another the passage of electric current through the filament, through the gas tube, etc. produces light output as well as heat. A 1000 watt hair dryer consumes 1000 watts, gets hot, but produces no light output. An electric motor consumes watts, prodces some wasted heat, and also does work ( rotation ). You notice that a motor using 1000 watts is no where near as hot as a 1000 watt bulb, so we can see there are different ratios of heat vs. watts for various devices.


As you have already realized, a very rough light output comparison is that a fluorescent bulb produces the approximate light output ( lumens, candlepower) as an incandescent of 4 times the wattage. The gas tubes are very efficient at producing light with not a lot of heat. The ballast also consumes energy and produces heat.


So, watts is a measure of electricity, and has some relation to heat, but is not related to light output. Light output is related to the physical charisteristics of the material: filaments ( tungsten, halogen), ionized gas( metal halide, mercury vapor. high or low pessure sodium), or even the new light emitting diodes. You may have noticed that municipalities almost everywhere are changing out the lamps in traffic signals to LED. The energy savings on an annual basis is enourmous.
Interesting.

But with the hairdryer you DO get light. It is the kind of light the element gives off on space heaters. That red light, when it gets hot enough. Space heaters on high (1500 watts...hair dryers on 1500 or 1850 watts as examples).

Regarding the electric motor comparison...that is a good point and interesting.
 
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Old 05-13-06, 06:06 PM
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Originally Posted by ibpooks
Heat transfer is not linear. This means that the hotter it is inside the jar relative to the ambient room temperature, the faster the jar will cool off. The jar at 230 degrees is loosing much more heat to the surrounding room than the 140 degree jar is. Therefore, the incandescent bulb is not only heating the jar to 230, but also releasing a lot of heat into the room. The CF bulb is only heating the jar to 140 and releasing much less heat into the room. This is where the hidden "four times" as much heat is.
Yes. Of course, now that you mention it. This makes sense. Heat transfer increases faster when the greater the differential. That explains why when you place a thermometer in a freezer, the temp drop from room temperature to a cooler temperature occurs very rapidly. But as the thermomter temperature approaches the actual freezer temperature, the temperature change becomes more gradual.

Everybody's smarts are coming through in this thread. Some great thinking, guys.

Oh...now after reading what you said, I am even MORE glad I am putting CFL's in light fixtures that are rated for lesser wattage bulbs, so I can get more light with less wire-damaging heat!
 
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Old 05-13-06, 06:08 PM
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Originally Posted by joed
It is simple. Watts does not equal temperature. You can have 25 watts and depending on what you do with it depends on the heat. My 25 watt soldering iron will get very hot compared to a 25 watt wall adapter for a radio.
You covered 1/2 of my observation. The other half had to do with lumens output in relation to heat. But thanks for the half you did. Everyone else seems on the same page as you on this one.
 
  #13  
Old 05-14-06, 05:28 AM
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Watts are a measure of energy per unit time. Since energy is neither created nor destroyed, but converted into different forms, all of the watts going into a lamp must come out somehow. Watts that are not converted to light must end up as something else, generally heat.

Light carries energy, thus you can in fact talk about 'watts' of light. Solar radiation, which includes both visible and invisible light, amounts to about 1200W per square meter just above the Earth's atmosphere.

The lumen is a measure of amount of light, but corrected for the sensitivity of the human eye. Thus 1 watt of a particular green light is defined as 683 lumen, but 1 watt of deep red might only be 10 lumen. 1 watt of far infrared would be _zero_ lumen, because you couldn't see it. For the mix of light that we call 'white', 1 watt of light is roughly 200 lumen.

For an ordinary incandescent lamp, you are looking at performance of perhaps 10-15 lumen output per watt of electrical input. As you see, most of the watts going into the lamp are coming out as something other than visible light. A _significant_ fraction of the 'wasted energy' comes out of the lamp as invisible infrared light. This energy doesn't raise the temperature of the lamp itself, but instead goes to heat the surroundings. The rest of the 'wasted energy' goes to heating up the lamp and by conduction the fixture. Incandescent lamps are so inefficient that you can pretty much consider _all_ of the power input as being converted to heat, with the little bit of light produced as a lucky side effect.

For other sorts of lamp, you will find different proportions of wasted energy versus used energy, and also different proportions of the different types of wasted energy. CFL lamps on the whole waste less energy; good ones might produce 50-60 lumen per watt. But they also produce less IR, and thus a larger fraction of the 'wasted energy' will remain inside the fixture.

In a 60W incandescent lamp, you get perhaps 3W of light out of the thing, with 57W of wasted energy. A large fraction of that wasted energy will leave the fixture as IR.

In a 20W CFL, you will get perhaps 3W of light out of the thing, with 17W of wasted energy. A smaller fraction of that wasted energy will leave the fixture as IR.

LED lamps are even worse in this regard; they have an efficiency of about 30 lumen per watt, produce almost no IR, and are themselves _very_ sensitive to the heat that they produce. A 5W LED lamp requires more heat sinking than a 50W halogen incandescent lamp.

-Jon
 
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Old 05-14-06, 09:14 AM
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Good observation about the glow from a hair dryer or portable heater. This is the very phenomenon that resulted in the invention of the incandescent bulb.(from Wiki: Incandescence is the release of electromagnetic radiation from a hot body due to its high temperature. The release of radiation is usually in the infrared (heat) region, known as thermal radiation, and the visible light region of the electromagnetic spectrum. Incandescence occurs in light bulbs, because the filament resists electron flow. This excites electrons in the filament material to jump to a higher atomic orbital and thus subsequently release a photon when they fall back to their original orbits. Depending on the energy difference between the two orbits, the emitted photon is of a different wavelength. The same process occurs when something is on fire or during an explosive or a combustion reaction.)

Most metals, when heated, glow. The color of the glow is related to the metal, and to the temperature. Our color spectrum numbers are related to the glow of iron or steel. 2700K is yellow , 4100K is much whiter etc etc.

So, in an incandescent bulb, the amount of light is related to the size of the filament. We can only heat the tungsten so had, then it burns, even in the vacuum. But we can put a larger filament...longer, more surface area....to get more light output.

When we talk about fluorescent or LED we are talking about completely different physics of light production, so it is apples and oranges. Heat is simply a side effect ( waste product ) of any particular method of light production. If heat is the desired effect( heat lamp for example) then we could say that the light produced is a side effect and a waste product.
 
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Old 05-14-06, 06:07 PM
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I am going to keep reading and trying to injest the last two posts for the next several days to see if I can get to the point I can carry this information in my head without forgetting what I read. Quite fascinating. You guys should have got a job working for Carl Sagan, or somebody, when he was alive. You could have helped analyze his BILLIONS and BILLIONS of stars to figure out where primordial light/heat went.
 
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Old 05-14-06, 08:39 PM
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Originally Posted by DaVeBoy
Yes. Of course, now that you mention it. This makes sense. Heat transfer increases faster when the greater the differential. That explains why when you place a thermometer in a freezer, the temp drop from room temperature to a cooler temperature occurs very rapidly. But as the thermomter temperature approaches the actual freezer temperature, the temperature change becomes more gradual.

Everybody's smarts are coming through in this thread. Some great thinking, guys.

Oh...now after reading what you said, I am even MORE glad I am putting CFL's in light fixtures that are rated for lesser wattage bulbs, so I can get more light with less wire-damaging heat!

I don't believe that the statement that heat transfer being faster the greater the differential is correct. I seem to remember a chemistry professor in college challenging us with the question if hot water freezes faster than cold water in an ice cube tray. We did the calculations and determined that heat transfer is constant, i.e. hot water takes longer to freeze than cold water, because it has to give off more energy before it can freeze. It has been a few years since college, though. And I have slept since then.
 
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Old 05-15-06, 01:25 PM
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Warning! Calculus content ahead. The basic heat transfer equation is:

Q = kA(ΔT/d)

Where:
Q: rate of heat flow
k: thermal conductivity (property of the material)
A: area of contact
d: distance of flow orthogonal to the area (A)
ΔT: difference in temperature

For this given system; k, A, and d are constant. Therefore, Q (rate of heat flow) varies linearly with ΔT (temperature difference). As temperature difference increases, the rate of heat flow increases proportionally. The actual heat flow (as opposed to the rate) increases more than linearly; this is the integral of the heat transfer equation.

The hot water, cold water experiment is an interesting one; but mostly because of the externalities which affect the results. Hot water does freeze faster despite the greater energy. Two of the primary causes of this are: convection at the surface of the hotter water causing greater heat transfer by air currents; and, hotter air in a freezer causes the thermostat to trip and the machine to be more aggressive in removing heat energy. In a "laboratory setting" where the air currents and cycling of the refrigeration equipment can be controlled, the hot water will freeze more slowly than the cold water.
 
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Old 05-15-06, 03:36 PM
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In a nutshell, Watts=work.

In an incandescent bulb, the light is made by heat, a lot of it.

In a flourescent bulb, heat is made by the consumed energy, but much more of the consumed energy comes out as light, per watt of energy consumed.
 
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Old 05-16-06, 02:00 PM
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Originally Posted by scott e.
I don't believe that the statement that heat transfer being faster the greater the differential is correct. I seem to remember a chemistry professor in college challenging us with the question if hot water freezes faster than cold water in an ice cube tray. We did the calculations and determined that heat transfer is constant, i.e. hot water takes longer to freeze than cold water, because it has to give off more energy before it can freeze. It has been a few years since college, though. And I have slept since then.
I think you may find the following interesting:

http://math.ucr.edu/home/baez/physic...hot_water.html
 
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Old 05-17-06, 04:46 PM
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Originally Posted by classicsat
In a nutshell, Watts=work.

In an incandescent bulb, the light is made by heat, a lot of it.

In a flourescent bulb, heat is made by the consumed energy, but much more of the consumed energy comes out as light, per watt of energy consumed.
Okay; what (er...cough cough...um..)..watt about THIS guys?: I have heard that watts do indeed give off a set amount of btus and the figure is aprox. 3.5 btu's per watt. (But...is there an asterisk somewheres that says this formula is only good for heating elements and does not necessarily work for different sorts of light bulbs or motors?) So, if watts is NOT the sole dictatorship of heat conversion...then why that formula?
 
  #21  
Old 05-17-06, 06:08 PM
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As far as I know (about as far as Buffalo), watts are a measure of power - energy per unit time in the strictest sense of the word. However, there are several formulas to obtain wattage which leads me to believe that there are a number of things that can be expressed in watts.

Essentially, though, P=E/t (Power=Energy/time)

With all manner of formulas you can put an energy value (joules) on both electricity and heat.

Example:

In terms of electricity, wattage is obtained through P=V*I (Power=Voltage*Intensity) This is rather simple though as this formula does not exactly apply to AC circuits. For our purposes, though:

3 amps at 120 volts = 360 watts. A device operated with this current and voltage for five minutes (300 seconds) produces or uses 108,000 joules of total energy.

To determine energy in terms of heat, you use Q=mcΔt (energy=mass*specific heat capacity*temperature change) So:

100 grams of water (4.19 j(g*C)) that undergoes a change of temperature of 20 degrees Celsius releases 8380 joules of energy. If this occurs for five minutes (300 seconds), then this is about 28 watts of power.

The way I understand it, wattage is a measure of power, energy per unit time, and energy is produced in several ways. The key here though is how much of the energy is used for heat and how much is used for light. There is no easy way I can think of to figure that out. There are probably scientific methods to determine how much heat and light a specific type of bulb or device will release based on material, use, and power (energy...)

Edit: I forgot to say that watts because of the number of formulas available to calculate them can also lead to finding a number of BTU's, but only because BTU's can be converted to other units.
 
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Old 05-17-06, 07:42 PM
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"..)..watt about THIS guys?: I have heard that watts do indeed give off a set amount of btus and the figure is aprox. 3.5 btu's per watt. (But..."

Put the emphasis on the "but"!

Watts is a measure of consumption of electrical power. It does NOT directly correlate to HEAT. The heat produced per watt is a function of what is consuming the electricty. In the HVAC world, they do use a rough figure of 3412 BTU per KW. But this is stictly used to compare an electric heat element to a gas burner. The heat strip converts almost 100% of watts to heat. NOT TRUE for a light bulb, even LESS true for fluorescent, etc, all the way to the "theoretical" perfect electric motor where NO WATTS are converted to heat.
 
  #23  
Old 05-17-06, 10:00 PM
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Originally Posted by DaVeBoy
I have always known the CFL's produce less heat that regular incandescent bulbs of the same wattage equivalency (based on light output).
This quoted statement was edited by me to make it true.

> I got thinking. If a CFL truly puts out the equivalent of light as an
> incandescent (say you are comparing a 60 watt bulb incandescent
> to a 13-15 watt 60 watt equivelent CFL)...then why
> isn't as much heat generated?

Lightbulbs are very inefficient some are a lot less efficient than others.


> if you were to instead factor in the wattage applied, instead
> of the lumens factor...then one could guess that the CFL
> would produce only 1/4 the heat

That's correct.

I note that the electrical energy all ends up as heat eventually -- even driving a perfect motor.
 
  #24  
Old 05-18-06, 04:50 AM
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Watts are watts. You can have 1 watt of electrical power flow, or 1 watt of heat flow, or 1 watt of light flux or 1 watt of mechanical power on a shaft or 1 watt of hydraulic fluid flow, etc.

If you have a resistance heater, it will convert electricity into heat. 1 watt of electricity in, 1 watt of heat out. 1 watt may be converted into units of BTU/hour; 1 watt if heat is a flow of 3.412 BTU/hour. One watt of power may be transmitted as a current of 1 A flowing at a potential difference of 1V. Or it could be a shaft torque of 1 newton meter rotating at 1 radian per second. Or it could be 1 cm^3 per second of hydraulic fluid flowing at a pressure of 1 megapascal. There are many different formulas for the different forms of energy and power, but they all boil down to the same _Watts_.

A lamp is simply a device which converts _some_ of the supplied electricity into light; the rest becomes heat. With a standard 60W incandescent lamp, 60W of electricity flows in, and get roughly 4W of light and 56W of heat flowing out. The light goes out into the room, gets absorbed by objects and the walls, and eventually even that 4W of light becomes 4W of heat

A _very_ good HID headlamp might take in 35W of electrical power and produce 10W-15W of light, with the rest coming out as heat.

A _perfect_ motor would take in 100W of electrical power and produce 100W of mechanical shaft power.

A _perfect_ generator would take in 100W of mechanical power and produce 100W of electrical power.

Unfortunately, we also have to add entropy into the equation. A 'perfect' device for converting heat into electricity could do no better than the Carnot limit. But this is for another class

-Jon
 
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Old 05-18-06, 05:57 PM
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I have read and like... and have learned quite a bit now... from all the replies above. This is quite fascinating. Pretty deep stuff.

Maybe we could all continue on some other thread discussing ethanol or methane gas energy conversions to see if we can run everything off of this and tell the arabs to.......

I have been pondering if we could all set out, curbside, mowed grass, for recyclers, who could convert it to methane. No Arabs to pay. No FARMERS to even pay.
 
  #26  
Old 05-18-06, 07:03 PM
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Originally Posted by DaVeBoy
I have been pondering if we could all set out, curbside, mowed grass, for recyclers, who could convert it to methane. No Arabs to pay. No FARMERS to even pay.
Funny you should say that...

I was talking to a guy last week, who informed me that some company takes grass clippings and compresses them into fuel pellets...

Still not good for the enviroment...
 
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