LED lighting circuit sizing

[mas13]

How do you calculate the circuit size for LED lighting? The published data on the watts for LED fixtures is lower than the actual power draw due to transformers and drivers.

 

[skeshesh]

I size the circuits based on maximum driver wattage. You did not indicate a location but let me also through it out there that out here in Ca I also use the rating of the driver not each LED array in title 24 compliance forms.

 

[dereckbc]

Driver plus LED wattage. The spec sheet should tell you. Typically 3 watts for each 1 watt of LED power.

This is the Dirty Little Secret about LED's. Once you take the driver/ballast wattage, along with the fudge of they only measure lumens in a focused spot for a milli-second pulse before the light heats up and decays, they are about on par with incandescent lamps with a terrible CRI

 

[WastefulMiser]

This is the Dirty Little Secret about LED's. Once you take the driver/ballast wattage, along with the fudge of they only measure lumens in a focused spot for a milli-second pulse before the light heats up and decays, they are about on par with incandescent lamps with a terrible CRI

dereckbc, could you clarify a little more? Thanks.

 

[IslandSparky]

Derek-- what equipment are you using? On drivers, we have been seeing 80+% efficiency, which isn't great but not terrible.

As for optics and CRI, I would agree that it isn't where it should be yet.

All told though, system efficacy for low-light applications is really pretty good compared to even fluorescents.

 

[dereckbc]

Its been a year or so since I looked into this, but I think I remember most of it.

The claimed efficiency (lumen per watt) is exaggerated or IMO misleading for 3 reasons.

1. They do not include the driver power.
2. LEDs have a very narrow beam of light and the measurements are are made on a focused at 1 meter. Move a few degrees off center and the brilliancy falls sharply.
3. When the measurement is made, it is with a cold lamp and only pulsed for a few milliseconds. LED output drops significantly after they heat up.

So when all be said and done, instead of say 130 lumens per watt as they claim, realistically they are in the neighborhood of 40 to 60 lumens per watt of low CRI heavy on Blue Light pollution.

So IMO they are a poor choice for interior area lighting. However they can be very good choices for task specific lighting like tail lights, emergency egress, head lights, flashlights, head lights, landscape, etc...

I think someday soon, the kinks and problems will be ironed out.

 

[steve66]

Its been a year or so since I looked into this, but I think I remember most of it.

The claimed efficiency (lumen per watt) is exaggerated or IMO misleading for 3 reasons.

1. They do not include the driver power.
2. LEDs have a very narrow beam of light and the measurements are are made on a focused at 1 meter. Move a few degrees off center and the brilliancy falls sharply.
3. When the measurement is made, it is with a cold lamp and only pulsed for a few milliseconds. LED output drops significantly after they heat up.

So when all be said and done, instead of say 130 lumens per watt as they claim, realistically they are in the neighborhood of 40 to 60 lumens per watt of low CRI heavy on Blue Light pollution.

So IMO they are a poor choice for interior area lighting. However they can be very good choices for task specific lighting like tail lights, emergency egress, head lights, flashlights, head lights, landscape, etc...

I think someday soon, the kinks and problems will be ironed out.

I do agree they play some games with the numbers, and you have to take all their claims with a grain of salt. But as long as you stay with a well know company with a good reputation, I don't think LEDS are near as bad as incandescent.

My understanding is that efficency wise, they are pretty close to fluorescent (with a much higher price, of course). Exactly which is more efficient (LED or fluorescent) is subject to debate because of how they play with the numbers.

The color is much better than it used to be also - most LED fixtures put out a light that looks very similar to a fluorescent fixture.

 

[zbang]

I have to disagree, but I'm working with some of these on a daily basis (disclaimer- the company builds an LED driver). BTW, I'm referring to fixtures and drivers sold into the commercial market, not big-box store specials for the homeowner.

1. They do not include the driver power.

The specs I've seen do include the driver, and most of the drivers I've seen are in the over 90% efficiency range. Rather a lot of engineering goes into them.

2. LEDs have a very narrow beam of light and the measurements are are made on a focused at 1 meter. Move a few degrees off center and the brilliancy falls sharply.

True for the raw LADs, but not the fixtures- I've got Lunera 2x2' panels that are even within ~100 lumens across the entire area. Also, some Calcullite downlights that have a pattern very similar to the incandescent version.

3. When the measurement is made, it is with a cold lamp and only pulsed for a few milliseconds. LED output drops significantly after they heat up.

Again, true for the raw LED, but not so for the fixture. Again, I've got some test units in the ceiling that are around 2400 lumen for maybe 60w input (plus <10% conversion loss), and those aren't the brightest.

[...], instead of say 130 lumens per watt as they claim, realistically they are in the neighborhood of 40 to 60 lumens per watt of low CRI heavy on Blue Light pollution.

So IMO they are a poor choice for interior area lighting..

Yes, 130 lumens per watt is fantasy at the moment, 40-50 is common. OTOH take a look at the offerings by Cree, Calcullite, Lunera, etc. They're quite good. Granted the CRI isn't that of a halogen incandescent lamp (i.e. 100), but they're getting much better. (FWIW, some of the fixtures use far blue/UV LEDS and a phosphor plate to get a nice warm white.

 

[dereckbc]

Yes, 130 lumens per watt is fantasy at the moment, 40-50 is common.

I believe if you go back and read I did say the true efficiency is 40 to 60 Lumen right? Although somewhat better than incandescent, it is not as good as quality CFL's and no where near Fluorescent T5 and T8 ratings. Our Federal Government will not even allow LED's to be used in any Federal buildings.

I think someday LED's will be more mainstream, but they are not ready yet IMHO, except for special task lighting and some architectural effects lighting, they are to be avoided for now. They are just too expensive with better options available. But hey, if your specs call for them, go for it.

 

[LEO2854]

Driver plus LED wattage. The spec sheet should tell you. Typically 3 watts for each 1 watt of LED power.

This is the Dirty Little Secret about LED's. Once you take the driver/ballast wattage, along with the fudge of they only measure lumens in a focused spot for a milli-second pulse before the light heats up and decays, they are about on par with incandescent lamps with a terrible CRI

thanks thats good info we all need to know about.

 

[dereckbc]

Sorry guys I did not mean to step on anyone toes. It has been a year since I last look into this so I am sure there have been some improvements since then. But unless the improvements have been revolutionary, I cannot think LED lighting has caught up or passed T5HO and T8 as of yet. Right now T5 lamps run about 82 to 88 CRI and up to 109 l/w.

So if someone has some up to date info I have overlooked please share. My mind is old, but still open.:grin: Where it affects me is I now tinker with Solar PV Battery systems and even CFL's can be a problem when ran on inverters and using low quality CFL's. A 13 watt CFL through an inverter can consume up to 55 to 60 watts from a battery. That is not good.

 

[LEO2854]

Heres a good link on leds. http://www.heroledstore.com/led-fluorescent-light-c-43.html

 

[ELA]

So if someone has some up to date info I have overlooked please share. My mind is old, but still open.:grin: Where it affects me is I now tinker with Solar PV Battery systems and even CFL's can be a problem when ran on inverters and using low quality CFL's. A 13 watt CFL through an inverter can consume up to 55 to 60 watts from a battery. That is not good.

I am curious how your measured the wattage consumed?

My experience has been that CFLs require a large "peak current" but the average or RMS is much lower. It is most likely these peak currents that cause issues with the inverter.

here is a 15 watt CFL current trace (o.5 amps /div)

 

[dereckbc]

I am curious how your measured the wattage consumed?

That is easy to answer. By measuring the DC current and voltage from the batteries feeding the inverter. Although I did make one error on the one tested. it was 33 watts from the battery.

They were using inexpensive 13 watt CFL's with a PF of .55, and the ballast consumed 3 watts. So once you take the PF, ballast wattage, and inverter efficiency (90%) into the equation you get (13 + 3) / .55 / .95 = 33 watts from the battery.

 

[ELA]

I would believe 31 VA.

 

[malachi constant]

Good LED fixtures make sense in limited applications. Lightolier's downlights (and the reasonable facsimiles put out by their competitors) cost a lot, and are not any more efficient than a comparable CFL, but have a 5-yr 50K warranty (or something like that), and include dimming capabilities out of the box.

I do not recommend them in most applications, but if you have a 24-7 application (such as a vestibule or corridor night light) then the saved maintenance pays for itself almost any way you choose to quantify maintenance costs.

Also if the Owner/Arch HAS to have a downlight, and it HAS to be dimmable, and they WON'T let you put in incandescent... Well, a dimmable LED is less expensive than dimmable CFL.

On our projects in colder climates I'll also specify LEDs at the exterior, in-lieu-of HID, as the LED you can put on a motion sensor and not have to worry about start-up time.

The only "dirty little secrets" I know about LEDs are that there are a lot of crappy ones out there that should never be allowed on the market. And even the folks selling good fixture lines know what to say and what not to say so as to frame their product in the best light. I recommend having a knowledgeable engineer or lighting designer take a look at any potential LED application where you plan on putting down good money.

 

[dereckbc]

Good reply malachi. I agree with you 100%. LED's at this time IMHO are for niche applications.