Brightness of the CharliePlex LED Matrix Bonnet

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tsutton
 
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Brightness of the CharliePlex LED Matrix Bonnet

Post by tsutton »

Hello,

I intend to use this matrix bonnet in one of my projects and need a value/number for it's brightness. Preferably in nits.
I've scoured the datasheet and can't seem to find anything relating to brightness
This is the matrix in question - https://www.adafruit.com/product/4121

Thanks!

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mikeysklar
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by mikeysklar »

There are 128 LEDs and the part numbers are listed in the schematic provided on the guides download page. Here are some of the white models used:

Code: Select all

XPEBWT-L1-0000-00D50 - White 111lm 350mA 2.9Vf 6200K 110°
XTEAWT-00-0000-00000LEE3 - White 114lm 350mA 2.85Vf 5000K 115°
45-21/LK2C-B50634C6CB2/2T - Cold White 2200mcd 20mA 3.25Vf 5650K 120°
https://raw.githubusercontent.com/adafr ... Bonnet.sch

You can also check their datasheets for further details and possibly NITS values.

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tsutton
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by tsutton »

Thanks a ton for the reply.

I think I've found the LED in question.

MFG P/N: 45-21/LK2C-B50634C6CB2/2T
Max millicandelas: 2600

My next question is; how would I convert this to nits? Here's how I would try this. Let me know if I'm completely off base or not.

There are 128 LEDs. So max from the matrix bonnet would be 332,800 mcd. This is 332.8 candelas. Well one nit is equal to one candela per meter squared. But aren't I missing the per meter squared part?

Now the area the LEDs take up on the board is 48mm by 24mm. Multiplying these together I get 0.001152 meters squared. But I'm not sure how to proceed from here to get candelas per meter squared.

Any help is appreciated.

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mikeysklar
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by mikeysklar »

Yeah, I can see how this approach gets complex having to deal with spacial layout.

Maybe a more efficient way to do this is to use:

mcd —> lumen —> nits

2600mcd —> 2.6 lumen —> (2.6 lum) / (3.426 nits converter) = .76 nits per LED

multiple by 128 leds = 97 nits

Does that seem close or way off?

I used this page for forumulas.

https://www.inhouseav.com.au/blog/begin ... rightness/

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adafruit_support_bill
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by adafruit_support_bill »

> But aren't I missing the per meter squared part?
You can calculate that from the dimensions of the bonnet: 65mm * 30mm = 1950mm^2 = .00195m^2

You also need to consider that the 'plex' in 'Charlieplex' stands for 'multiplexed'. The individual LEDs are not on full time, so your calculation would need to be scaled by the effective duty-cycle. A good read of the data sheet should shed some light on that.: http://www.issi.com/WW/pdf/31FL3731.pdf

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tsutton
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by tsutton »

mikeysklar wrote: Wed Feb 08, 2023 9:38 pm Yeah, I can see how this approach gets complex having to deal with spacial layout.

Maybe a more efficient way to do this is to use:

mcd —> lumen —> nits

2600mcd —> 2.6 lumen —> (2.6 lum) / (3.426 nits converter) = .76 nits per LED

multiple by 128 leds = 97 nits

Does that seem close or way off?

I used this page for forumulas.

https://www.inhouseav.com.au/blog/begin ... rightness/
That's pretty much how I did it. But I didn't go to lumens. I just went straight from mcd to candelas. But I'm not sure that mcd to candelas account for the m^2 portion of nits since 1 candela per m^2 equals 1 nit. What do you think?

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adafruit_support_bill
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by adafruit_support_bill »

You definitely need to divide the candelas by the m^2. It takes a LOT more candelas to make a Jumbotron appear as bright as a hand-held display.

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tsutton
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by tsutton »

adafruit_support_bill wrote: Thu Feb 09, 2023 12:00 pm You definitely need to divide the candelas by the m^2. It takes a LOT more candelas to make a Jumbotron appear as bright as a hand-held display.
So would the brightness of the Charlieplex matrix bonnet be as follows?

332.8 candelas divided by 0.00195m^2 = 170,667 candelas/m^2

Does 171k nits seem right for the brightness of this small matrix? I don't have a frame of reference.

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adafruit_support_bill
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by adafruit_support_bill »

So would the brightness of the Charlieplex matrix bonnet be as follows?

332.8 candelas divided by 0.00195m^2 = 170,667 candelas/m^2
You would also need to factor in the duty-cycle as mentioned above. In a multiplexed display, the individual LEDs are not on 100% of the time.
Does 171k nits seem right for the brightness of this small matrix?
'nits' is not a measurement unit that I use, so I do not have anything to compare it with.

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mikeysklar
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by mikeysklar »

Doing some searches for devices that typically use nits shows:

* Apple watch 200 nits
* Phone screen 400 - 1000 nits
* Laptop screen brightness required to read in direct sunlight > 1000 nits
* Average LCD backed LCD TVs 450 nits
* OLED TVs 700 - 1000 nits
* QD-OLED TV 2000 nits

171k seems high to me.

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tsutton
 
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Re: Brightness of the CharliePlex LED Matrix Bonnet

Post by tsutton »

adafruit_support_bill wrote: Fri Feb 10, 2023 7:55 pm
So would the brightness of the Charlieplex matrix bonnet be as follows?

332.8 candelas divided by 0.00195m^2 = 170,667 candelas/m^2
You would also need to factor in the duty-cycle as mentioned above. In a multiplexed display, the individual LEDs are not on 100% of the time.
Does 171k nits seem right for the brightness of this small matrix?
'nits' is not a measurement unit that I use, so I do not have anything to compare it with.
I'll keep in mind the duty-cycle and multiplexing in general. Thanks!
mikeysklar wrote: Sat Feb 11, 2023 2:23 pm Doing some searches for devices that typically use nits shows:

* Apple watch 200 nits
* Phone screen 400 - 1000 nits
* Laptop screen brightness required to read in direct sunlight > 1000 nits
* Average LCD backed LCD TVs 450 nits
* OLED TVs 700 - 1000 nits
* QD-OLED TV 2000 nits

171k seems high to me.
Very good point. I'm with you; 171k seems high. I think I have enough information here for my purposes. I really appreciate everyone's help!

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