absolute limit for light bulb wattage

[lemur]

I started to post this in the thread about light bulbs but I thought it might be considered hijacking. As I understand it, a 15watt cfl produces as many lumens as a 60watt incandescent, both of which can be replaced with a 5watt LED(or was it 3?). I would think LEDs are the limit for lamp efficiency but is any greater efficiency possible?

 

Once total lighting efficiency is reached, what will be the next great "efficient technology race," iyo? Or maybe the better question would be what technology has the greatest potential for energy-efficiency increases after light-bulbs?

[Cap'n Refsmmat]

http://www.ccri.edu/...keefe/light.htm

 

A source of 100% efficiency would produce 680 lumens per watt.

 

A 100-watt incandescent bulb radiates 1,600 lumens, so a hypothetical 100%-efficient bulb would need to be only 2-3 watts to match it.

 

Note that lumens are weighted towards light in the visible range -- that is, you can have a device 100% efficient in turning electricity into light, but if it's infrared light, it'll produce 0 lumens. Most incandescent bulbs put out a lot of infrared light, and presumably other devices have similar problems.

 

So yes, greater efficiency is hypothetically possible, but a device with 100% efficiency in turning electricity into visible light is unlikely.

 

This article has a table of luminous efficiencies including theoretical limits for different devices:

 

http://en.wikipedia.org/wiki/Luminous_efficacy

[SMF]

A practical note. We could get a light device with very high efficiency, but it is not so good unless the manufacturers can also be persuaded to produce a power supply for converting from household AC to whatever is needed, that doesn't turn on until the light, or whatever, does. Those little cube power supplies that come with various electronic devices can draw as much as 5 watts while idling, even when the appliance is turned off. Someone needs to look at the big picture. SM

[lemur]

A 100-watt incandescent bulb radiates 1,600 lumens, so a hypothetical 100%-efficient bulb would need to be only 2-3 watts to match it.

 

Note that lumens are weighted towards light in the visible range -- that is, you can have a device 100% efficient in turning electricity into light, but if it's infrared light, it'll produce 0 lumens. Most incandescent bulbs put out a lot of infrared light, and presumably other devices have similar problems.

 

So yes, greater efficiency is hypothetically possible, but a device with 100% efficiency in turning electricity into visible light is unlikely.

As I understand it, LEDs generate a single wavelength of light, e.g. blue or red, so no energy goes into making infrared, microwaves, etc. Is there any energy loss within the LED itself, or does the inefficiency of LEDs have to do with their electrical components?

 

 

 

A practical note. We could get a light device with very high efficiency, but it is not so good unless the manufacturers can also be persuaded to produce a power supply for converting from household AC to whatever is needed, that doesn't turn on until the light, or whatever, does. Those little cube power supplies that come with various electronic devices can draw as much as 5 watts while idling, even when the appliance is turned off. Someone needs to look at the big picture. SM

You mean AC/DC converters? You're right that those waste energy when the appliance isn't connected and should be unplugged.

 

Still, the problem as I see it is that as light bulbs and electronics use increasingly lower amounts of energy, other applications such as various forms of heating/cooling use so much that efficiency increases in lighting and electronics appear relatively insignificant. For example, if you run a 15W cfl bulb for 10 hours/day, i.e. @300hours/month, that is 4.5kwh. Now if you reduce that by 60% by switching to LED's you save @3kwh/month. But if you look at the electric usage of a household with climate control, household usage can be 500kwh+/month. Since I don't use a/c or electric heat, my usage is often 200kwh/month or less, but 3kwh saved by going from CFL to LED is still just a drop in a bucket.

 

I assume that the majority of the energy I use is for heating water, using an electric range, and the refrigerator. I suppose the water heater and refrigerator could theoretically be made more efficient by coupling them as some kind of heat-pump thermal exchange system. I don't know how cooking could be made more efficient, though, except by designing some kind of solar pressure cookers or something like that.

 

Climate control is the Mt. Everest of energy-efficiency challenges, imo, at least in residential and consumer applications. There may lots of industrial gains to be made but since those are kept private for the most part, I don't know how you could survey and analyze energy applications there. Maybe a really useful way to reduce industrial energy waste, though, would be to combine industrial applications that use large amounts of energy such as bakeries and other oven-using industrial facilities with consumer applications such as malls. That way, heat used for the industrial application could passively benefit the neighboring retail space.

 

 

[SMF]

Here is a thought. I have many lights that don't draw any electricity at all. They are the ones that I turn off when they are not needed. Fly over the country on a red eye flight and look out the window. Large buildings, parking lot lights, street lights, night lights are on all over the place. I wonder how much electricity goes to this. Turn them off, and when security or safety is needed an efficient proximity or movement switch can turn them on as needed. SM

[swansont]

Here is a thought. I have many lights that don't draw any electricity at all. They are the ones that I turn off when they are not needed. Fly over the country on a red eye flight and look out the window. Large buildings, parking lot lights, street lights, night lights are on all over the place. I wonder how much electricity goes to this. Turn them off, and when security or safety is needed an efficient proximity or movement switch can turn them on as needed. SM

 

That works for your yard but there are lights used for lighting large areas do not turn on very quickly, and may not respond well to a higher frequency of cycling them on and off.

[lemur]

Here is a thought. I have many lights that don't draw any electricity at all. They are the ones that I turn off when they are not needed. Fly over the country on a red eye flight and look out the window. Large buildings, parking lot lights, street lights, night lights are on all over the place. I wonder how much electricity goes to this. Turn them off, and when security or safety is needed an efficient proximity or movement switch can turn them on as needed. SM

Yeah, and since you're turning them off anyway, why not send all the people who live around them south to warmer climates to take advantage of solar heating?

[SMF]

Swansont. I presume what you are referring to are lights, like sodium vapor lamps, that are very efficient when run for a long time but take a large warm up period to come on. It would be silly to use such a lamp for instant-on security, but somebody should be able to easily pick the correct technology for each specific application, or to decide that light-as-needed won't work at all. For example, there are streets in cities and towns that are left lighted all night when there is only a couple of cars or pedestrians per night who need it so a different lighting technology should be used. It is not simple, but this strategy could certainly save a lot of power.

 

Lemur. I think maybe your response is an attempt at humor, but I don't get the joke. The only people who are deriving warmth from their lighting are those that run incandescents. They are effective but expensive heaters. SM

[lemur]

Lemur. I think maybe your response is an attempt at humor, but I don't get the joke. The only people who are deriving warmth from their lighting are those that run incandescents. They are effective but expensive heaters. SM

No. I thought that while you're turning off lights to save power, you might want to turn of heaters to save even more. I suppose it is humorous that if you're going to turn the lights off anyway, you might as well send people south. It would save energy though.

[SMF]

Lemur come on, please be serious. Moving people between cold and warm regions not only requires transportation fuel but, in addition, twice the living space. All it takes to keep reasonably cool in the summer and reasonably warm in the winter at an acceptable cost is efficient appliances and good insulation. SM

[lemur]

Lemur come on, please be serious. Moving people between cold and warm regions not only requires transportation fuel but, in addition, twice the living space. All it takes to keep reasonably cool in the summer and reasonably warm in the winter at an acceptable cost is efficient appliances and good insulation. SM

Well, the idea of forced migration for energy savings is ridiculous I will admit. But the question of whether it would make a significant different in energy savings is another question. Does insulation really make enough of a different to close the gap between heating in northern and southern climates?

[SMF]

Lemur. Insulation makes a huge difference. Here is a personal anecdote-- Around 1990 I had a friend who moved his lab to a university in northern Ohio. He purchased a house that had been constructed by a builder who was really into energy conservation. The first time I visited it was well below freezing and there was six inches of snow on the ground. There was a 500 gallon tank of hot water fed by solar water heaters on the roof that was used to heat the house so the natural gas heater usually ran only in the early AM. The day I was there it was cloudy but the water coming from the solar heater to the tank was 120 degrees F. In the summer heat the house was comfortable with no installed air conditioning system. The well done insulation in the house is what made the difference. This is not rocket science and usually pays for itself in less than 10 years after which the house continues to save. Like big business, home owners and lending agencies are more concerned with the short term. SM

[Phi for All]

Yeah, and since you're turning them off anyway, why not send all the people who live around them south to warmer climates to take advantage of solar heating?

!

Moderator Note

lemur- You need to stop derailing threads with off-topic comments like this. If you want to talk about alternative energy saving measures, start another thread. This one is about the efficiency of light bulb wattage.