Maximum Wattage vs LED wattage

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KP2

Senior Member
Location
New Milford, CT
Hello everyone, I am working on a landscape lighting project, and hit a crossroad.

The NEC is clear to indicate the maximum fixture wattage is to be used; however the customer is going with all LED lighting.

The maximum wattage is 35W and the LED is 5 watts; imagine the difference in the amount of branch circuits, and transformers needed for the LED install.

I would like to use the LED ratings and capitalize on the energy savings of the LED; that's why they are being used in the first place, right.

Is there an exception I'm missing, or a LED label I can put on the fixture to allow the LED wattage to be used.

Thanks
Kevin
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The issue here is if the fixture can take a bulb greater than what you use then you must use that number. I know it is a bit of a pita now especially since many of the incandescent bulbs are not available anymore. I would ask the authority having jurisdiction and see if he/she would allow you to calculate it with the LED. Of course you have to figure the largest LED that would be able to work in there.

The other issue is the type of fixture-- most LED bulbs do not like to be in an enclosed fixture so unless these are recessed cans you can have issues with the heat from LEDS
 

hbendillo

Senior Member
Location
South carolina
I do a lot of commercial work and some manufacturers will change the "Maximum Lamp Wattage" labels in their fixtures for us to a lower value. Do check with the manufacture to make sure you can use LED lamps with the fixture. LED lamps may have to be used in an enclosed fixture and some of the LED's are not rated to be used in enclosed fixtures. There are some manufacturers that make a LED lamp that can be used in enclosed fixtures.
 

mwm1752

Senior Member
Location
Aspen, Colo
Hello everyone, I am working on a landscape lighting project, and hit a crossroad.

The NEC is clear to indicate the maximum fixture wattage is to be used; however the customer is going with all LED lighting.

The maximum wattage is 35W and the LED is 5 watts; imagine the difference in the amount of branch circuits, and transformers needed for the LED install.

I would like to use the LED ratings and capitalize on the energy savings of the LED; that's why they are being used in the first place, right.

Is there an exception I'm missing, or a LED label I can put on the fixture to allow the LED wattage to be used.

Thanks
Kevin

Kevin will you specify the code section? you are talking about exterior landscape lighting/ Remote Transformer?/ If you use a remote transformer for the lo volt circuit then the branch circuits are rated on the transformer not the individual fixture -. The amount of load for a lighting branch circuit based upon individual fixture driver & its rating is exactly that -- just because an individual wants to use energy efficient lamps does not change the equation for what the continuous load is able to be. The next individaul may want to install 35w lamps as they are approx 90% less expensive,
 

iwire

Moderator
Staff member
Location
Massachusetts
Kevin will you specify the code section? you are talking about exterior landscape lighting/ Remote Transformer?/ If you use a remote transformer for the lo volt circuit then the branch circuits are rated on the transformer not the individual fixture -. The amount of load for a lighting branch circuit based upon individual fixture driver & its rating is exactly that -- just because an individual wants to use energy efficient lamps does not change the equation for what the continuous load is able to be. The next individaul may want to install 35w lamps as they are approx 90% less expensive,

Regardless he has to calculate the lighting circuit at fixture value even if low voltage.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
What aspect of the fixture limits the lamps that can be installed to a maximum of 35W?

My guess is that the fixture is only thermally capable of handling 35W, and has a label that states this limitation...but that the actual lamp holder will permit the installation much higher wattage lamps. The only thing keeping the customer from putting in 'more lamp than the fixture can handle' is that label.

(Yes, there might be a fuse, or a thermal cut-off)

So I think that hbendillo's answer is actually plausible.

Be sure to check that the LEDs you wish to use are compatible with the fixtures, in terms of things like the _LED_ itself overheating.

-Jon
 

Electric-Light

Senior Member
Lamp watt for lamp watt, LEDs produce the most heat at the fixture.

A 35W LED is less efficient than a 35W incandescent in converting electricity into radiant energy. A 35W may contain 30W of radiated energy, mostly in infrared.

A 35W LED may only radiate 10W and require the remaining 25W removed by conduction.
They're only able to shed the heat by conduction and convection rather than radiating. The allowable temperature for LEDs are much lower, so this further limits the allowable power.
 

cad99

Member
Location
ND
Maximum Wattage vs LED wattage

Living the dream one nightmare at a time.
 
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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Lamp watt for lamp watt, LEDs produce the most heat at the fixture.

A 35W LED is less efficient than a 35W incandescent in converting electricity into radiant energy. A 35W may contain 30W of radiated energy, mostly in infrared.

A 35W LED may only radiate 10W and require the remaining 25W removed by conduction.
They're only able to shed the heat by conduction and convection rather than radiating. The allowable temperature for LEDs are much lower, so this further limits the allowable power.

Let's try to make some sense out of this. An LED is more efficient than an incandescent in converting electrical energy to optical energy in the visible spectrum.
The incandescent also does radiate a lot of heat in the infrared range where it is not useful, so the heat which has to be conducted away could indeed be less than for an LED/driver assembly with the same input power.
But that LED will be giving several times as much visible light as the incandescent with the same input power.

Your statement is logically correct, but somewhat misleading in the context of real installations.
Another problem, though, is that the LED and driver cannot tolerate as high a temperature as an incandescent bulb. That puts a premium on the lamp assembly to conduct heat away over a lower temperature differential. :)
 

KP2

Senior Member
Location
New Milford, CT
Thank you for the replies; I am referring to article 220.14(D).

The fixtures and LED lamps are compatible, so I do not worry there; and there is nothing in the fixture to prevent an incandescent lamp from replacing the LED.

Plus, not many hardware stores carry the LED lamps needed for these fixtures.

Anyway, I think you all have answered my question, I need to size everything to the maximum wattage of the fixture. If I had more time, or used the brand more often I would reach out to the manufacture to see if I could get a replacement label.

Thanks again folks; it's better to be safe anyway.
Kevin
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Hello everyone, I am working on a landscape lighting project, and hit a crossroad.

The NEC is clear to indicate the maximum fixture wattage is to be used; however the customer is going with all LED lighting.

The maximum wattage is 35W and the LED is 5 watts; imagine the difference in the amount of branch circuits, and transformers needed for the LED install.

I would like to use the LED ratings and capitalize on the energy savings of the LED; that's why they are being used in the first place, right.

Is there an exception I'm missing, or a LED label I can put on the fixture to allow the LED wattage to be used.

Thanks
Kevin

you are stuck with the maximum possible wattage you can put in that fixture.

dunno if this would work for you, but if you use a LED fixture
that draws 12 watts, then 12 watts is what you calc with, yes?
the customer probably isn't thrilled with changing fixtures, but
that is the only option you have.

i've used these a fair bit for commercial grade lighting, and like them.
http://focusindustries.com/led-technology
 

Electric-Light

Senior Member
Let's try to make some sense out of this. An LED is more efficient than an incandescent in converting electrical energy to optical energy in the visible spectrum.
The incandescent also does radiate a lot of heat in the infrared range where it is not useful, so the heat which has to be conducted away could indeed be less than for an LED/driver assembly with the same input power.
But that LED will be giving several times as much visible light as the incandescent with the same input power.

I am discussing the reasons behind lower wattage limitations. Incandescent lamps shed the wasted energy as radiated energy, so it doesn't have to be "sunk" into the heatsink at the fixture. So, incandescent lamps put out more radiated watts per watt of input. Make sense?

Your statement is logically correct, but somewhat misleading in the context of real installations. Another problem, though, is that the LED and driver cannot tolerate as high a temperature as an incandescent bulb. That puts a premium on the lamp assembly to conduct heat away over a lower temperature differential. :)

Which I covered. It's the higher percentage of watts that must be drawn away by conduction as well as the lower tolerance to temperature level, which is why you end up with a 5W limit in a fixture that can handle a 35W incandescent.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
To be clear, Electric-Light is providing a sound theoretical basis for why a fixture might have different wattage ratings for LED versus incandescent lamps.

The original question was directed at why it might be _desirable_ for a fixture to have a lower wattage rating for LED lamps, or why it might be desirable for a fixture as installed to have a lower wattage rating label than the fixture itself might be able to handle.

-Jon
 

kwired

Electron manager
Location
NE Nebraska
I am discussing the reasons behind lower wattage limitations. Incandescent lamps shed the wasted energy as radiated energy, so it doesn't have to be "sunk" into the heatsink at the fixture. So, incandescent lamps put out more radiated watts per watt of input. Make sense?



Which I covered. It's the higher percentage of watts that must be drawn away by conduction as well as the lower tolerance to temperature level, which is why you end up with a 5W limit in a fixture that can handle a 35W incandescent.

One also has to consider the fact that to get similar light output you will not be replacing a 35 watt incandescent with a 35 watt LED, the LED that puts out same light output as the 35 watt incandescent maybe only uses 5-7 watts of input power.
 

hbendillo

Senior Member
Location
South carolina
Hello everyone, I am working on a landscape lighting project, and hit a crossroad.

The NEC is clear to indicate the maximum fixture wattage is to be used; however the customer is going with all LED lighting.

The maximum wattage is 35W and the LED is 5 watts; imagine the difference in the amount of branch circuits, and transformers needed for the LED install.

I would like to use the LED ratings and capitalize on the energy savings of the LED; that's why they are being used in the first place, right.

Is there an exception I'm missing, or a LED label I can put on the fixture to allow the LED wattage to be used.

Thanks
Kevin

I know someone else has already covered this but if you are using low-voltage landscape lighting why aren't you using an LED landscape light fixture rather than an low voltage incandescent fixture with an LED lamp? Probably cost I would imagine. But if you did the former you would have a lot less transformers. Depending on the application, I have used line-voltage incandescent style landscape light fixtures with LED lamps. No transformers to deal with. You just need to make sure you use the correct lamp.
 

Electric-Light

Senior Member
One also has to consider the fact that to get similar light output you will not be replacing a 35 watt incandescent with a 35 watt LED, the LED that puts out same light output as the 35 watt incandescent maybe only uses 5-7 watts of input power.

To get a similar output yes.
Desk lamp says 40W max, so anyone with any sort of common sense would know that they can't use a 100W bulb. However, it's a fairly reasonable assumption to say "hey, I can use a 100W equivalent 20W LED, because it's under 40W". So my post addresses the point on the reasons for the second LED specific rating.

Why not is a better answer than "just because you can't"
 

kwired

Electron manager
Location
NE Nebraska
To get a similar output yes.
Desk lamp says 40W max, so anyone with any sort of common sense would know that they can't use a 100W bulb. However, it's a fairly reasonable assumption to say "hey, I can use a 100W equivalent 20W LED, because it's under 40W". So my post addresses the point on the reasons for the second LED specific rating.

Why not is a better answer than "just because you can't"
That 20 watt LED in a luminaire designed for a 100 watt lamp doesn't accumulate the same heat in the luminaire as when a 100 watt incandescent is installed, it may still trap enough heat to effect the operation/life of the LED lamp or driver though.

What I am saying is you can possibly have a luminaire that is not really compromised by the use of the "equivalent" LED, but the LED could be compromised by the design of the luminaire, but put too large of an incandescent lamp in same luminaire and now you compromise the luminaire and maybe the lamp as well.
 
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