Lumens vs. Watt ratings

[jjhall5150]

Does anyone know if there is a "rule of thumb" to estimate the amount of lumens emitted from a par can LED of specific wattage.

I recently spoke with a colleague who had some very bright par cans but was not sure what the wattage rating was per LED. He did explain that his company advertises them as emitting between 4000 and 5000 lumens.

I am going to be in the market for some high powered uplighting next year and am unsure if I should be looking a 3w, 7w, or 10+w units. I would think that I would not need to go above 30' from floor to ceiling for illumination

Thoughts?

 

[JD]

Very little correlation. We can "assume" that all other things being the same, a higher wattage unit will put out more lumens, but that's about where it ends, and here is why:

Different light sources have radically different efficiencies. An Arc lamp will give you more light and less heat per watt compared to an incandescent. LED lamps are very efficient as well.

Even when you have the same basic lamp, lumen output can vary greatly due to age. Also, "long life" lamps will give you less output than the same style lamp with a normal life rating.

For example, a 1000 watt PAR 64 NSP lamp can be obtained with the standard 400 hour lifespan, but there is also an industrial version of the same lamp that has a 2000 hour lifespan. The long life lamp has significantly less lumen output.

LED fixtures also vary greatly. This is especially true if you compare an older generation to a newer generation fixture. LED technology is continually moving forward and towards higher outputs with the same wattage consumed.

Although LEDs have a fantastic life, not much real world experience is out there regarding output change over life. We know the white phosphorus does age and shift a bit in color. Also, the junctions do degrade over time dropping output, but with these lifespans, it's hard to compare a new one to an old one!

Most newer units use multi-output LED devices. These vary greatly depending on the manufacturer.

 

[sk8rsdad]

Mike Wood has a couple of good articles on the challenge of measuring luminous efficiency. These are a few examples of a number of interrelated articles on his site.

http://www.mikewoodconsulting.com/articles/Protocol Fall 2008 - Color Prejudice.pdf
http://www.mikewoodconsulting.com/articles/Protocol Fall 2011 - Total Lumens Revisited.pdf

 

[BillESC]

Does anyone know if there is a "rule of thumb" to estimate the amount of lumens emitted from a par can LED of specific wattage.

I recently spoke with a colleague who had some very bright par cans but was not sure what the wattage rating was per LED. He did explain that his company advertises them as emitting between 4000 and 5000 lumens.

I am going to be in the market for some high powered uplighting next year and am unsure if I should be looking a 3w, 7w, or 10+w units. I would think that I would not need to go above 30' from floor to ceiling for illumination

Thoughts?

I'd recommend you look at Blizzard's Puck Fab 5. This fixture features seven 15w RGBAW diodes. All the power you could ask for and a complete color palette. The street price is $ 255.55

 

[porkchop]

If they're giving you lumens that's what you're actually interested in since that describes how bright the fixture is. Wattage is a measure of power usage and in the world of LED's is really only useful to tell you how many of them you can plug into a given power source.
If you're trying to visualize how bright 4k - 5k lumens is look for the rating on fixtures you already know. For instance a standard source 4 PAR EA MFL is advertised as having 9,890 field lumens. Fixture brightness is a tricky thing. Subtractive vs. additive mixing makes it even harder to compare in exact terms, but on average I would expect the LED fixture you mentioned to be around half as bright as a Source 4 Par.

 

[PeteEngel]

And when looking at fixtures, field lumens and lumens are different. A fixtures LEDs may generate 9850 lumens, but not all of those lumens are coming out the front of the light, or out of the light as a useful beam of light. It kind of depends on the type of light. A fixture without any lensing will push more of the LED Lumens out the front than a profile (for example). The best way to make sure a fixture will work for you is to get one to look at. If it doesn't do what you want, move on.

 

[JD]

One other thing about fixture brightness:
A conventional fixture works by starting with white and subtracting by using gel. An LED fixture works by adding colors together and ending up with white. When you get into the deep primary colors, LED fixtures may out preform a conventional fixture that had a much higher lumen rating. This is especially true at the deep blue end of the spectrum.

 

[RickR]

And when looking at fixtures, field lumens and lumens are different. A fixtures LEDs may generate 9850 lumens, but not all of those lumens are coming out the front of the light, or out of the light as a useful beam of light. It kind of depends on the type of light. A fixture without any lensing will push more of the LED lumens out the front than a profile (for example).

I beg to differ: What you say applies to conventional fixtures where you have a rating for the lamp by itself. LED units only perform as a whole and so the rated total lumens is for the fixture. Even more confusing is that LED chips don't have a fixed output. The harder they are driven the brighter they go, but for less time. So the driver in a fixture is a major factor in its total brightness.

• Beam Lumens = light output in the field of the beam, which is half brightness of the center.
• Field lumens = out to 10% of the center.
• Fixture lumens = the total of the unit in all directions, event the glow from the power indicator on the back.
• EDITED correct terms

The best way to make sure a fixture will work for you is to get one to look at. If it doesn't do what you want, move on.

That is pure truth and wisdom!

To answer the OP's question 1/4 to 1/3rd the wattage of an incandescent is a very rough estimate. It is very hard to get good data from theatrical fixture makers. They don't want it to all be about the total brightness, and to a large extent I agree. The color range, the features and cost are at least as important. After all if you need more light you should hang another fixture. Now "cost per lumen" is a measure I would love to see for all fixtures sold.

Oh yes, add the deep color vs white light issue and comparing wattage to incandescent goes out the window.

 

[derekleffew]

• Field Lumens = light output in the field of the beam, which is half brightness of the center.
• Beam lumens = out to 10% of the center.

Above appears contradictory to the traditional, accepted definitions of beam angle and field angle.
-----
See the articles linked to in post #3.
.

 

[DELO72]

You are talking apples and oranges. PARs have their output measured in Centerbeam Candlepower due to the nature of the light. "lumens" is almost a misnomer in this regard and not a very applicable unit of measurement for comparrision has it refers (in the PAR spec.) to the total lumen output of the burner (capsule) behind the lens of the PAR, and not the CbCp of the light coming out of the lens.

And I concur with Derek- Beam Angle intensity is commonly accepted as the intensity of the center, hottest area of the light, to where it drops off to 50% intensity of that value. Field Angle intensity is to where it drops off to 10% of the center intensity. At least that is how it has always been defined in everything I have ever read or seen.

 

[RickR]

Above appears contradictory to the traditional, accepted definitions of beam angle and field angle.
-----
See the articles linked to in post #3.
.

You caught me typing faster than thinking. Sorry

As for CbCp that is one measure of a beam type light. As I'm sure you know Mark there are many other ways to measure a fixture, or a lamp or the brightness at a spot, or, or... I wish I could find the link, but Sri Rahm over at GE did a nice webinar a while ago on the various ways to measure brightness. If anyone has a link it is an excelent refresher on this basic aspect of light.

 

[RickR]

As for CbCp that is one measure of a beam type light. As I'm sure you know Mark there are many other ways to measure a fixture, or a lamp or the brightness at a spot, or, or... I wish I could find the link, but Sri Rahm over at GE did a nice webinar a while ago on the various ways to measure brightness. If anyone has a link it is an excellent refresher on this basic aspect of light.

Found the link - unfortunately you have to sign up (free) at http://www.gelearningcentral.com They have lots of other useful stuff too.


I recommend the videos so you get his verbal explanation to go with the slides.