LED lighting

[jahilliard]

I'm trying to do a VD calculation for some pole/parking lot lights. The LED lights show them to be 89 watts at max input watts. Do I need other info due to the fact they are LED or can I use the 89 Watts for the calc?

 

[JDBrown]

You'll also need the input power factor. All of the voltage drop calculations I've ever done have amps as one of the input parameters. If you just divide the Watts by your system voltage, the number of amps you get will only be correct if your power factor is 1.0.

Other than that, you just need the usual information: voltage, phase, wire size, wire material, distance from first light to source, distance between lights.

 

[qcroanoke]

I'm trying to do a VD calculation for some pole/parking lot lights. The LED lights show them to be 89 watts at max input watts. Do I need other info due to the fact they are LED or can I use the 89 Watts for the calc?

Do you mean voltage drop?
or volt amps?

 

[jahilliard]

hmm....I don't see an actual PF available. I'm under the impression 80% would be a fair estimate??

 

[jahilliard]

VD being voltage drop...trying to size wire for 5 -120V pole lights LED (89 watts) total run of 600'

 

[JDBrown]

hmm....I don't see an actual PF available. I'm under the impression 80% would be a fair estimate??

It's very dependent on manufacturer. I've seen LEDs with 85% input PF, but I've also seen them with 70% input PF. My first recommendation would be to contact the manufacturer and ask for their technical department -- they should be able to tell you the input PF or input amps. I usually have pretty good luck going that route when information isn't listed on the cut sheet. Be prepared to spend some time on hold, though. Also, this approach is very dependent on who the manufacturer is and how helpful/knowledgeable their people are.

If contacting the manufacturer doesn't work, I would do some conservative calculations assuming a very low power factor -- maybe 60% or 65% -- and some less conservative calculations assuming a power factor of 80%. You may find that it doesn't make any difference, and your wire will be sized the same either way. In that case, you're done.

If, on the other hand, you end up with a larger wire size for the lower power factor, you are left in the unenviable position of having to guess at information that should have been provided for you. You will have to weigh the potential cost savings of using smaller conductors (and possibly smaller conduits) against the possibility of the voltage drop being too high and causing your lights to not function as intended. Personally, in that situation I pretty much always go with the conservative estimate because I'd rather have the project cost a little more up front than run the risk of having to go the client and sheepishly explain that I screwed up selecting the wire size, and now we're going to have to replace all these wires (which ends being quite a bit more expensive).

 

[gar]

130829-1426 EDT

Use a Kill-a-Watt EZ, about $30 at Home Depot.

A small LED I measured read 123 V, 0.11 A, 7 W, 14 VA. 0.54 PF. Larger units may be required to have a better PF.

Just take an RMS ammeter and measure the current.

.

 

[steve66]

Looking at a Lithonia D series, the 89 watt version draws .89 amps at 120 volts, and the amps are proportional to the voltage. So they have the same PF no matter what the supply voltage is.

These fixtures are available anywhere from 52 watts to 209 watts, and the higher wattage lights seem to have a PF in the high 80's, while the lower wattage ones seem to be in the low 80's.

Steve

 

[gar]

130829-2115 EDT

steve66:

Interesting.

On the small LED I tested RMS current is close to constant, about 0.1 A, from 60 V thru 140 V with sine wave excitation. Power and light output does vary with voltage.

.

 

[jahilliard]

So if there is drop in voltage, say from 120 to 105, what could potentially result as far as the LED light itself? would it become dim, change color slightly, flicker?? I'm curious if anyone has actually tested or experienced what happens.

 

[gar]

130829-2217 EDT

jahilliard:

For the LED I just referenced it reads about 25 footcandles at 120 V and about a 30" distance. At 100 V it is about 23 and at 60 V about 18. No flicker. This is all sine wave excitation from a Variac. No real color change.

Go buy one from Home Depot and play with it, about $10. The part number is Cree BA-1904527OMF-12FDE26-1U_00 2113.

.

 

[GoldDigger]

So if there is drop in voltage, say from 120 to 105, what could potentially result as far as the LED light itself? would it become dim, change color slightly, flicker?? I'm curious if anyone has actually tested or experienced what happens.

If the "white" LED uses a combination of several different colored LED dies, then it may change color somewhat when the driver goes out of regulation at the dim end. The different colors may have slightly different minimum voltages.

Flickering is certainly possible if the LED driver is not designed for dimming service.
Some LED drivers are designed to maintain a fixed brightness over a wide voltage range while others are deliberately sensitive to either voltage or conduction phase angle to allow them to be deliberately dimmed.

But 105 volts is not likely to trigger any of these effects.

 

[broadgage]

Many but NOT ALL LED driver circuits are designed to give proper operation over a wide range of input voltages.
I have one here that is intended to work from 90 volts up to 270 volts.

 

[augie47]

Curious, how many 89 watt fixtures are we talking about ?
Playing with the voltage drop formulas, its gonna take a whole lot of fixtures before you would need to worry about PF especially with the acceptable percentage of drop.

 

[steve66]

130829-2115 EDT

steve66:

Interesting.

On the small LED I tested RMS current is close to constant, about 0.1 A, from 60 V thru 140 V with sine wave excitation. Power and light output does vary with voltage.

.

I'm not sure what kind of LED you are using, but the OP is talking about a commercial fixture that will have an integral driver. The driver is probably a switching mode power supply. And the driver's job is to keep the output power and lumens constant when the voltage changes. So it makes sense that doubling the voltage would cut the current in half.

Basically, they just won't have the light output variation you are seeing. That's a good thing - nobody wants to see a row of light get gradually dimmer as the voltage drop increases near the end of the run. And nobody wants to see the lights flickering and getting dimmer and brighter as spikes and sags and surges come along from the utility or other equipment.

Everyone keeps asking "Can I dim standard fluorescent lights or standard LED lights." If they don't say they are dimmable, then they probably have a ballast or driver specifically made to prevent dimming. The only way to dim these is to push the ballast or driver beyond its design range.

 

[gar]

130830-1509 EDT

steve66:

The design of the ballast will determine the characteristics of the operation of the lamp. The major point I was making was that jahilliard should perform an experiment on his lamp to determine its characteristics.

The small bulb I used in the test was a Cree BA-1904527OMF-12FDE26-1U_00 2113. This is designed as a dimmable device on phase shift dimmers, but also dims on sine wave excitation. In contrast a dimmable GE CFL dims somewhat with a phase shift dimmer, not nearly as good as an incandescent, but on sine wave excitation has relatively stable light output until it just quits at around 100 V. The GE is a good way to minimize flickering on motor startup transient voltage drops.

To really know how a lamp will perform under some set of conditions you need to do some of your own testing.

.