# LED color, brightness, and uniformity tester



## tddh007 (Jul 29, 2013)

Hi everyone,

I just registered to ask a question regarding measuring LEDs. I want to know what kind of test equipment is recommended for testing LED color, brightness, and uniformity. 


I am a complete novice when it comes to lighting, so if my question is too vague please fill free to ask here and I will answer what I can.

Thank you!


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## AnAppleSnail (Jul 30, 2013)

White or color LEDs? UV or IR?
Lumens or watts output?
Color = tint?
Uniformity = consistency?
What about CRI?

Edit: A light meter is a good basic tool for white lights. There are some DIY spectrometers that can be used to explore the output frequency of lights.


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## tddh007 (Jul 30, 2013)

AnAppleSnail said:


> White or color LEDs? UV or IR?
> Lumens or watts output?
> Color = tint?
> Uniformity = consistency?
> ...



HI AnAppleSnail,

Thanks for the reply. Let me answer your questions.
-White LEDs
-Lumens
-Color...unsure on this
-Uniformity- color and intensity consistency through a light pipe
-CRI? 

As for the LED I am planning to test is a Kingbright CCT 8000k.

Thanks


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## Cataract (Jul 31, 2013)

For color and CRI I do believe you would need a spectrometer type of meter, then relate the data to some tables. Color and CRI are very subjective. I might also be corrected by more knowledgeable CPFers in the following posts. The same equipment could be used to map the beam , but that needs a mechanical way to move the source or the light sensor with step motors. Are you looking into buying this equipment or just curious?


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## Harold_B (Jul 31, 2013)

What type of light pipe? Are you edge lighting or more like a fiber optic. How much light are we talking about? How big of an area and at what distance from the exit aperture? 

As a first pass assuming a fiber type I would recommend an Ocean Optics spectrometer and an integrating sphere such as a Labsphere. That will get you the spectra / Correlated Color Temperature and the Color Rendering Index of both the source LED and the output from the light pipe. This could be significant depending on material choice and path length if color shift is important. 

For uniformity you could go a couple of ways (we do both) but it will depend somewhat on the application. A goniometer that can measure in the near-field will allow you to characterize the output. We have also found an astronomy software that is really handy called MaxImDL. You can import a photo of the output from a device under test and analyze the image. We use these two pieces of equipment / software for correlation data for building optical models.


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## tddh007 (Aug 5, 2013)




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## stevethumb21 (Sep 6, 2013)

tddh007 said:


> Hi everyone,
> 
> I just registered to ask a question regarding measuring LEDs. I want to know what kind of test equipment is recommended for testing LED color, brightness, and uniformity.
> 
> ...





In my opinion.....the light output can be measured with the help of Lux meter or photo meter. These meters have various functions like data hold function, over level indication, etc. They can measure both luminosity as well as brightness. They are portable an light weight. You can get them anywhere or buy them from online stores.


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## Laser2012 (Sep 16, 2013)

What are better online stores for LED lights? I am looking for one trade partner that we can continue a long-term cooperation.


stevethumb21 said:


> In my opinion.....the light output can be measured with the help of Lux meter or photo meter. These meters have various functions like data hold function, over level indication, etc. They can measure both luminosity as well as brightness. They are portable an light weight. You can get them anywhere or buy them from online stores.


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## stevethumb21 (Oct 19, 2013)

Laser2012 said:


> What are better online stores for LED lights? I am looking for one trade partner that we can continue a long-term cooperation.



You can visit INITIAL-LED. 

I have been using their lights since last two years and I am quite happy with the response. 

They have got huge variety too.


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## degarb (Oct 19, 2013)

stevethumb21 said:


> In my opinion.....the light output can be measured with the help of Lux meter or photo meter. These meters have various functions like data hold function, over level indication, etc. They can measure both luminosity as well as brightness. They are portable an light weight. You can get them anywhere or buy them from online stores.



Luminosity? Doesnt compute. Lux. Meters only meaure brightness at a single point. Lumen meters are quite expensive. There are tricks to get lumen guess, I guess.

I wonder if anyone has a compiled list of metering devices, by price ranking. Like on battery
university.


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## Cataract (Oct 19, 2013)

-Luminosity is the term for brightness reading in lux, footcandle or similar units. The brightness is read by a small sensor so, yes, it is a single point reading. 

-There is no such thing as a lumen meter; total lumen is read by a luminosity sensor while the sensor and light are placed inside an integration sphere that reflects all of the light being emitted.

-I calibrate light meters and by experience, although there are no actual standards on the general calibration of such devices except for certain specific scientific applications, they are all pretty much as accurate unless you're going to buy a flat-spectrum 10 000$ machine (which will also read both UV and IR and not really give a representative figure). Some have an integrated sensor (i.e. the sensor is part of the unit) and others have a sensor attached by a wire. The latter is a little more convenient as you can have the sensor mounted on a rig or integration sphere and still read it with ease, but they are slightly more expensive. Sensor sizes do vary. I would suggest a larger sensor for integration spheres and a smaller one for single-point measurements, although it might not make much of a difference in the end.

*[EDIT]:*
I just realized I said something a bit stupid: Light meters are by convention calibrated using a ~2700K bulb and an IR filter (usually halogen and I gotta double-check that kelvin statement if I can find the paper. I'll update this post if I do find it.) I also have an LED source to calibrate some meters and, though all meters give pretty much the same reading with the incan bulb, the readings can differ greatly when using an LED source. An educated guess would mean that the cooler the LED, the more the readings can differ. Most sensors include an UV filter and only the more recent ones (don't ask for a date, could go as far back as 10 years for all I know) include an IR filter. The IR filter can make quite a difference on the reading for both incan and LED. [/EDIT]


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## Cataract (Oct 22, 2013)

Had to edit my last post as I omitted an important detail ^^^^^


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