Incandescent efficiency

Resistance DECREASES and overall (power) output falls off? Yes, at zero, the power is zero.

What you want is maximum power transferred to the media that protects your citrus. Gotta measure it.

That seems to be correct intuitively. The relationships are far from linear, as the bulb temperature does down, so does its resistance. The spectral distribution of the emissions will move toward the infrared as filament temp decreases (which is good for you). But the proportion of the power dissipated by conduction (instead of radiation) will go up as the bulb runs cooler. Radiation is probably what you want. It will be converted to heat by the absorbing surfaces, even at a distance while heat conducted away will d s mainly in the vicinity of the fixture. So you don't want to run too cool.

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Yes the lower the voltage the lower the efficiency in converting to light and the higher the efficiency in converting to heat.

At one volt the bulb will be nearly 100% efficient in converting to heat BUT the amount of electrical power in and the amount of heat power out, while nearly equal will be very small.

Even at normal voltage the eff converting to heat is still very high so I suggest you simply adjust the voltage for the desired amount of heat that you want and don't worry about efficiency. Its very high in any case.

Mark

Understood. And power falls off quicker than resistance, no doubt.

Can't adjust voltage -- they are run of the AC mains. :>

What I was "thinking aloud" is that I can increase bulb longevity by running them at reduced voltage. *And*, not suffer any significant change in (in)efficiency.

Since adjusting the mains is out of the question (and, putting

*almost* anything in series with the mains will undoubtedly throw away more power than I am "saving"), the only legitimate solution is to wire bulbs in series. This will give me roughly half the power (total) in a pair of bulbs. :<

OTOH, they will run significantly cooler (each dissipating

1/4 what they would otherwise) so there will be less chance of them shattering in the cold.

Trick will be to find the sweet spot that gives me power without requiring a boatload of lamps!

Thanks!

Yes.

Won't be a significant loss. It's not like the heat is going anywhere *other* than up into the tree.

Understood.

I think the goal is to keep air moving through the tree to "discourage" cold air from settling (stagnating) on the leaves and fruit. I think the most energy efficient solution is a good soaking of the ground (water == thermal mass) during the daylight hours, *some* heat source under/in the tree and a fan to gently circulate air throughout the tree.

Of course, this only really works when it isn't truly cold (most citrus are good to ~28F -- though it depends on the variety and how *long* it stays at that temperature).

At lower temperatures, I spray the trees with a fine mist throughout the night. We've managed to keep all of the trees alive through a series of five "below 20" evenings a year or two back (the trees bore no fruit the following season but no wood was lost).

Next year I will try to automate this. (we haven't had any cold nights -- yet -- this year)

Thanks!

The Wiki entry on filament bulbs has the sort of basic info you need on the non-linear changes in lifetime, light output and power used as a function of applied voltage for filiament bulbs:

Roughly speaking a 5% decrease in operating voltage will give you twice the bulb life but 20% less light using around 8% less power. This means that depending on the number of bulbs in your chain you will need a power resistor to drop 5% of mains (US 100v) at the bulbs rated current.

So back of the envelope say 500W of filament lights is 5A at 100v and would need a >25W 5 ohm ballast resistor to drop the unwanted voltage. Take care working with mains voltages.

Since the light is waste you don't need to leave the bulb envelopes clear. If they were surface silvered or dipped in fireproof paint then just about all the power that goes into them comes out as thermal IR or convection currents of warm air. Both should help your trees. This might shorten their lifetime outdoors if rain occurs and the glass envelope objects to the thermal shock (particularly if they get close to 100C). Possibly worth experimenting a bit though since you only want the heat.

Regards, Martin Brown

Well..one could use a step-down transformer (like a filament transformer) wired in series opposing to the input line voltage - in order to get a lower driving voltage. Say a 12V filament transformer to decrease drive by 10 percent WRT input line voltage, or a 24V filament transformer for 20% reduction.

I would think that with a good heat source, one would not need a fan..heat rises and cold air settles - giving circulation in the desired direction - - just put the heaters below the trees and not in large gaps between them.

• IF that power resistor heats up enough, it can be added to the heater array for the trees. Otherwise, it would be more efficient to use a series bucking transformer (about 6V filament transformer for 5% of line).

On a sunny day (Wed, 20 Jan 2010 23:15:07 -0700) it happened D Yuniskis wrote in :

Triac light controller.

Such bulbs are mostly constant current sources, the resistance depends on the temperature. So 2 in series will likely use more then 1/2 the power, as temperature will drop and resistance will drop. Try it and measure the current.

The power (losses) dissipated in the transformer would then be removed from where I *want* that heat. OTOH, adding bulbs in series reduces the total power dissipated *but* the bulbs can still be located under the trees -- and we can always add more.

Big transformer. We're moving ~3KW+ currently.

Yes, I've already been there. :>

Light bulbs are nice, inexpensive, easy to replace "power resistors".

Looking at more like 3000W (I'd have to check for the exact figure). I.e., a 20A GFCI will not support the current load.

Exactly. That's why I think putting pairs in series (i.e., so each sees half the line voltage and thus 1/4 power) will be a triple win: lifetime, (in)efficiency, and less chance of thermal shock.

I think I'll take the PCB oven and use it backwards -- stuff some bulb combinations inside and measure temperature rise over time for various combinations.

This is nonsense. Filament resistance does rise as the filament gets hotter, but nowhere near enough to make a tungsetn filament light bulb a constant current device, at least not when most of the energy put into the biulb is being radiated; once you reach this regime, the power radiated by the filament increases as the fourth power of temperature, so extra voltage doesn't heat the filament all that much more , because most of the extra power is being radiated (though not as visible light, so the efficnecy - as a visible ligth source - is still dire).

This is true, though the logic Jan used to get there isn't up to much.

Good advice.

-- Bill Sloman, Nijmegen

I think the problem is that any transverse (?) airflow (e.g., wind) can easily offset the effects. If that wind is cold, then the fact that it is moving is no bargain as it just replaces cold air with cold air.

Also, recall these are *trees*, not "shrubs". E.g., the smallest is 15 feet tall and easily 15 ft wide. It's hard to move air through that volume just with convection.

On a sunny day (Thu, 21 Jan 2010 08:31:46 -0800 (PST)) it happened Bill Sloman wrote in :

There is a factor 10 between the resistance of a cold bulb and a hot one.

Snipped rest of climate crap.

Please remember to keep the spraying actively into the next morning, until the air temperature is above 0 C. Cutting off the spraying too early may cause just more damage.

Injecting a lot of water into an area will keep the area at 0 C until all water has been frozen. By providing a sufficient amount of water, not all water will be frozen and hence the temperature does not drop below 0 C.

Sloman will use any topic as the basis of lame insults. I assume most of his life works like that.

John

Yes. I have noted that the temperature actually *falls* most precipitously just AFTER Sun-up! Some days, this has meant

7A is the coldest time of the "night"! :-(

The trees already are plumbed for irrigation (not "drip" in these cases since I need to be able to put a LOT of water into the ground around them and don't want to have water running for 12 hours just to get that sort of volume...). My plan is just to remove the "heads" from the irrigation lines and attach nozzles (on poles). Then, just have the irrigation controller run them for 5 minutes every hour when the temperature is below freezing.

(so far, I have only had to mist the trees once -- over a period of several days -- in more than a decade)

Yes. And I think it also affects the plant itself as water is taken up into it.

The ideal is not to lose fruit. Next, not to lose foliage (it's odd seeing an evergreen citrus devoid of foliage!). Finally, not to lose *wood*.

Interesting to think of how citrus farmers have to do this on a larger scale. But, then again, they are in the *business* of producing fruit (I just want fresh squeezed orange juice :>)

Yep, when I lived north of Shea Boulevard, where night-time hard freezes were the norm, I'd simply run the aerator on the swimming pool, fog the back yard, and prevent freezing of my orange, grapefruit, lemon and lime trees. ...Jim Thompson

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