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Old 12-26-2011, 01:59 PM   #41
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Originally Posted by braumeister View Post
Actually, it's a bit more complicated than that. The low voltage give you less of a voltage drop, not more. Also, the bulbs (halogen) are considerably more efficient. Also, I don't want very bright light, just enough to turn a totally dark night into a low visibility situation.

But my point was merely that the total cost of the system is quite reasonable at only $100 a year.
Not really - as I said "all things being equal, a low voltage system will be less efficient than a high voltage system."

The voltage drop will be higher (%-wise, which is all that matters in efficiency) in a lower-voltage, higher-current system.

And a halogen high voltage bulb of X watts will be more efficient than a halogen low voltage bulb of X watts. And there is still the transformer loss - possibly considerable loss if it helps keep manufacturing cost low. No extra transformer in a line-voltage system.

I'm just trying to point this out, as I know some people are under the mistaken belief that "low voltage" means "low electrical use" and it isn't the case. If low voltage helped efficiency, we'd see low-voltage transmission lines, not high voltage ones.

While we are at it, one 100W bulb will be more efficient than two 50W bulbs (more light for the same power in), ~ 21% more efficient.


ooops - cross posted with sailor; I obviously agree with sailor too!

-ERD50
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Old 12-26-2011, 02:30 PM   #42
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Yes, physics is fun.
However, you ignored my point.
Enough.
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Old 12-28-2011, 11:04 AM   #43
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Originally Posted by ERD50 View Post
Why low voltage? All things being equal, a low voltage system will be less efficient than a high voltage system.

More voltage drop in the conductors for one (low voltage means higher current for the same watts, so more loss). The second thing is that low voltage incandescent bulbs are relatively less efficient, since the filament needs to be short/thicker for the same wattage, and a higher percentage of heat is conducted away by the standoffs that hold that short, thick filament.

Plus, you lose a bit in the transformer used to convert the high to low voltage. There are losses going to low voltage, and no gains at all.

IOW, four 50 watt bulbs consume 200 watts, regardless of voltage. But you get fewer lumens out of the low volt bulbs, and there are more losses delivering those 200 watts.

-ERD50

For me it is because the wires and lights are in the garden or on a tree in the yard...

I don't want someone digging and get a nasty surprise...
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Old 12-28-2011, 11:23 AM   #44
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RE: low voltage lighting.

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For me it is because the wires and lights are in the garden or on a tree in the yard...

I don't want someone digging and get a nasty surprise...
Sure, that's a good reason to go low voltage. It's also why I have a few solar/battery 'marker' lights on my property. Efficiency isn't the driving factor in that case, ease of installation and safety were. So if low voltage makes sense installation-wise (or any other reason), then you are set. Just be aware the efficiency will suffer by some amount (for a given light level).

Separately, I didn't really 'ignore' braumeister's point, I was just commenting on the side issue relevant to this thread about the efficiency of such lighting. I do find that many people equate 'low voltage' with 'low electricity usage' and it's just not valid. I didn't want anyone to get the wrong idea. That's all.

-ERD50
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Old 12-28-2011, 11:30 AM   #45
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RE: low voltage lighting.



Sure, that's a good reason to go low voltage. It's also why I have a few solar/battery 'marker' lights on my property. Efficiency isn't the driving factor in that case, ease of installation and safety were. So if low voltage makes sense installation-wise (or any other reason), then you are set. Just be aware the efficiency will suffer by some amount (for a given light level).

Separately, I didn't really 'ignore' braumeister's point, I was just commenting on the side issue relevant to this thread about the efficiency of such lighting. I do find that many people equate 'low voltage' with 'low electricity usage' and it's just not valid. I didn't want anyone to get the wrong idea. That's all.

-ERD50
I agree with your post.... but I would also hate to have someone put in lighting that is dangerous because they think they can save a bit using high voltage... when my BIL was alive, he used to change gas yard lights to low voltage... and he was very surprised on how many people just ran a 110 volt wire buried 3 inches and had a standard bulb when they did the conversion...

As to the other post, I still do not think CFL is the way to go for on demand lighting... just not enough savings IMO... now, if you plan on the light going on at night and staying on for many hours or until morning... you have some savings...
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Old 12-28-2011, 01:53 PM   #46
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I agree with your post.... but I would also hate to have someone put in lighting that is dangerous because they think they can save a bit using high voltage... .
And I would never suggest that anyone put safety second to a few $ savings in electricity. I hope no one thought I implied that in my post.



Quote:
As to the other post, I still do not think CFL is the way to go for on demand lighting... just not enough savings IMO... now, if you plan on the light going on at night and staying on for many hours or until morning... you have some savings..
Agreed. CFL in a motion light that comes on for 10 minutes now and then does not make much sense. I was going to add (someone may have already mentioned it), some motion detectors or dawn-dusk switches are not designed for CFLs, they can handle only non-reactive (regular old bulbs) loads.

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Old 12-29-2011, 09:15 AM   #47
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I have my motion detector set to be very sensitive to motion so the light comes on easily and has a wider range of detection this way. Better to shine on the bad guys if they try to approach the house and jump the fence near the edge of the property. And if they are casing my house, they will see the motion sensing light come on if someone walks by on the sidewalk occasionally. As a result my light is on probably a few hours per night in total. I think I have it set to stay on for 10 or 15 minutes per activation.

Saving 120 watts (30 watts for CFL versus 150+ watts for halogen or incandescent) equates to about $15 a year if my lights are on 3 hrs/night. I don't recall the outdoor CFL's being much more expensive than incandescent flood lights or halogen. And so far, a couple years into the first CFL bulb, no problems with frequent cycling causing premature bulb failure. My energy savings have more than paid for the $20 fixture replacement and the $5 bulb (vs my old halogen set up).

But yes, you don't want to spend hundreds to change out a motion detector using incandescent or halogen to a CFL compatible type. For me it was around $20 and an hour of unscrewing old fixture, splicing wires, screw on new fixture and tune the settings to desired result. And a $5 bulb.
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Old 12-29-2011, 09:17 AM   #48
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I was going to add (someone may have already mentioned it), some motion detectors or dawn-dusk switches are not designed for CFLs, they can handle only non-reactive (regular old bulbs) loads.
I learned that the hard way and had to return the $15 non-cfl compatible for the $20 CFL compatible light fixture.
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Old 12-29-2011, 09:19 AM   #49
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Fuego,
I like the idea of using the CFL bulbs outside, but I suspect they won't work too well through a cold Minnesota winter. I know my standard flourescent bulbs in the garage won't turn on.
That's the conventional wisdom. I think the bulbs I bought had an "operating temperature range" on them, and they work fine where I live (low temps in winter are usually not much lower than +20F except a day or two per year). On particularly cold days they are a little dim when they first come on (but still plenty to see where you are going).
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