How to calculate lighting power of a textured LEM ?

[derei]

I need to emulate a LED stripe and making geometry for each LED is not an option right now (I have to use many stripes of different lengths), thus I've tried it and it's ok.

What I'm thinking now is to use a texture for LEM. A black rectangle with white dots on it. But I need to be as accurate as possible.
I know that one LED element on the stripe consumes ~0.07W and its efficiency is about 42 lumen/watt.

My question is if I can reproduce this using a textured Light Emitting Material, and how?

[Fletch]

Like this?
:>: Subject: LED strip (MODEL AND TEXTURE INCLUDED IN .SKP SCENE)


For calculation of light emission, study this:
Subject: Lighting Made Simple

...

To calculate the power for light emitter surfaces is a bit more complicated.

Let's say you have a large space to light, and you want to render with Easy 1-7. Let's presume you want to light it all quickly and evenly with as few lights as possible.
With Easy 09 and 10, 200 lights is going to render similar in speed to 10 lights. This is not so with Easy 1-7.

We just said above that we don't want to 'fake' lighting, typically, so what are we talking about here? Occasionally you will need to use some 'creative lighting' to render quickly yet still look good. So for your average space, just light it as is, but for a huge gymnasium with 50-200 light sources, there may be a better way...anything over 15 lights is considered a "lot" of lights for "Easy" render settings 1-8. 200 lights castings soft shadows for objects in a room can take a lot of calculation time in Easy 1-7.

The process for lighting large spaces for rendering with Easy 1-7 is 2 steps:

1. Create a light emitting plane at the height of the lights for the space.
2. Give an emittance value to the light emitting plane equivalent to all the lights in the room.

Step 1:

• Create a plane below the ceiling at the height of the lights for the space should be. Hold if off from the side walls about 2 feet (60cm).
• Paint it with a white color.
• Rename the color to “Emit Ceiling”
• Apply the Template “Emit 100w/m2” and set it to “Invisible” type emitter.

Step 2:

• If the total lights in the space would equal 50 lights each at 200watts, then we need 50x200=10000w.
• Select the face in SketchUp and look at the Entity Info to see the size in meters squared. Remember that this emittance has an efficiency of 2.1%, similar to a real world incandescent light bulb.
• The Emit Ceiling Plane is 5540sq ft (515 sq meters) at 100w/m2 it will emit 515m2x100w = 51500watts. To make it 10000w, we take 10000w and divide by the size 515 sq meters = 19.4 w/m2
• So set emitter to 19.42 w/m2 for a 515 square meter plane to make it mimick the light output of an emitter powered by 1000 total watts.
• Now your ceiling just became a 10000watt light bulb and equals 2 lights in Twilight because a rectangle will be triangulated. This will render much more quickly than 50 spotlights in Easy 1-7.
• For the ceiling fixtures now use a fake emitter material to make them appear lit.

[derei]

Yes, like that,
Ok, this is for a LEM with full color. This applies to textured as well? Or I should calculate only the ACTUAL EMITTING areas on that texture? As you very well pointed it out on the attached render, the texture is black with dots. I assume that only the non-blacks will emit light.
So, how do I do it? I calculate the area of the support geometry, or only the non-blacks? Also, it depends on image resolution used as texture or not? (will the number of pixels in that "LED" dot affect its power?)

[Jpalm]

Lighting calculations made simple!


For calculation of light emission, study this:
Subject: Lighting Made Simple

...

To calculate the power for light emitter surfaces is a bit more complicated.

Let's say you have a large space to light, and you want to render with Easy 1-7. Let's presume you want to light it all quickly and evenly with as few lights as possible.
With Easy 09 and 10, 200 lights is going to render similar in speed to 10 lights. This is not so with Easy 1-7.

We just said above that we don't want to 'fake' lighting, typically, so what are we talking about here? Occasionally you will need to use some 'creative lighting' to render quickly yet still look good. So for your average space, just light it as is, but for a huge gymnasium with 50-200 light sources, there may be a better way...anything over 15 lights is considered a "lot" of lights for "Easy" render settings 1-8. 200 lights castings soft shadows for objects in a room can take a lot of calculation time in Easy 1-7.

The process for lighting large spaces for rendering with Easy 1-7 is 2 steps:

1. Create a light emitting plane at the height of the lights for the space.
2. Give an emittance value to the light emitting plane equivalent to all the lights in the room.

Step 1:

• Create a plane below the ceiling at the height of the lights for the space should be. Hold if off from the side walls about 2 feet (60cm).
• Paint it with a white color.
• Rename the color to “Emit Ceiling”
• Apply the Template “Emit 100w/m2” and set it to “Invisible” type emitter.

Step 2:

• If the total lights in the space would equal 50 lights each at 200watts, then we need 50x200=10000w.
• Select the face in SketchUp and look at the Entity Info to see the size in meters squared. Remember that this emittance has an efficiency of 2.1%, similar to a real world incandescent light bulb.
• The Emit Ceiling Plane is 5540sq ft (515 sq meters) at 100w/m2 it will emit 515m2x100w = 51500watts. To make it 10000w, we take 10000w and divide by the size 515 sq meters = 19.4 w/m2
• So set emitter to 19.42 w/m2 for a 515 square meter plane to make it mimick the light output of an emitter powered by 1000 total watts.
• Now your ceiling just became a 10000watt light bulb and equals 2 lights in Twilight because a rectangle will be triangulated. This will render much more quickly than 50 spotlights in Easy 1-7.
• For the ceiling fixtures now use a fake emitter material to make them appear lit.

[/quote]

[Fletch]

Calculations are rarely simple, it's a fact of life.

As far as calclulating precise light output of LED texture that's part black and part color... I really have no idea.
How could one even know in the end that it's "correct"? The best you can do is two small simple test scenes for comparison to see if it makes a difference.
you will have to adjust exposure of the final rendered image, for sure.
you will have to make every light in your rendering exactly precise as well, or the accuracy of this particular LED emitter will become pointless.

Basically, it's a watts per meter squared calculation.

watts divided by the surface area in meters! (come on, Jpalm, it's not so tough, really?!)

But if you want to be very precise, export a simple test material scene with the LED material painted exactly correct scale on a quick test cube, export to xml, open in Kerkythea, change power of LED emitter material to Lumen output, and then save that material to a material library and use that.

I wouldn't bother calculating the black vs light areas of the image. I would assume the lumen output is the lumen output.

[Jpalm]

Thanks Fletch. I think!

[derei]

I don't need to be VERY precise, just not to have let's say a 3x stronger illumination. Because I want to offer a solution for a client and this is for preview purpose. If it will be too bright, it may mislead the client and this is something I don't want to.
I'll try a test scene with same geometry, same power settings, but with texture vs solid color, to see differences in intensity.

[Fletch]

I'll try a test scene with same geometry, same power settings, but with texture vs solid color, to see differences in intensity.

we would be interested to see the results.

[derei]

TEST RESULTS
I used This texture as LED Stripe (colored @ 3500K: rgb 255,193,141)
(forum won't let me to add more than 3 images, so I had to place this one in external link)

attached my admin

LED_Stripe_3500_K.png (683 Bytes) Viewed 15720 times

Knowing that (this particular) LED has a power consumption of 0.07W and 42lm/W efficiency (compared with 16lm/W of a ordinary light bulb), I found out that I need a x2.625 multiplier for the value that I calculate using the formula (total_power/emitter_area).

So, for a 50cm strip I had 30 LEDs with a total of 2.1W absorbed power.
Total area of the strip: 8mm x 500mm = 4000mm^2 (0.004m^2)
Resulted power: 2.1/0.004 = 525 W/m^2
Calculated power (efficiency multiplier): 525 x 2.652 = 1378.125 W/m^2 (rounded to 1380 W/m^2)
Adjusted power (only for LED area) one LED is a 2mm x 2mm square. 30 LEDs have 0.00012m^2 => 2.1/0.00012 = 17500W/m^2; with efficiency multiplier we have: 17500 x 2.625 = 45937.5W/m^2 (rounded to 45938W/m^2)

Then I made 3 tests:

1. Calculated power (1380W/m^2) with TEXTURE

LED Stripe_1a.jpg (241.39 KiB) Viewed 15736 times

2. Calculated power (1380W/m^2) with SOLID COLOR (rgb 255,193,141)

LED Stripe_2a.jpg (358.44 KiB) Viewed 15736 times

3. Adjusted power only for LEDs (45938W/m^2) + TEXTURE

LED Stripe_3b.jpg (483.22 KiB) Viewed 15734 times

Conclusion
It seems that Textured LEMs area needs to be calculate according to non-black zones.

I'm wondering if adding a normal-map for LEDs (to make small indentations where the LED is), would better emulate the "spot" effect. As it is now, it emits in all directions and the "spot" effect seen in most LED strips disappears. Too bad that I don't know to use KT to make a material with Normal Map ... and TL as it is now, seems to not "know" how to use a normal map... thus it would be a "must" feature.

-If anyone is willing to create that material, I would be glad to provide a normal map for it.
Maybe it can be made in such manner that in Color channel to use SketchUp texture, and only the normal-map channel to have a preloaded texture.
--

[Chris]

Nice results.

I would be very surprised that light emitting materials change their emission direction based on a normal map. You might be able to use an IES emitting texture though...