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Rove
12-01-2013, 04:50 PM
Hi all,

I want the color of a translucent lamp to change color according to the light intensity it receives, is that possible? I'm using LW v11.6. I can't seem to find a fitting nodal setup but I have to admit that I have no tech background whatsoever. It's all trial and error for me using the available nodes. I currently am experimenting with Ray Length input.

Rove.

Sensei
12-01-2013, 05:09 PM
Light intensity in real world depends on inverse square law.
So the farther from light source, the less photons is colliding with object.
Simply plug Item Info World Position and Spot Info World Position to Math Vector Distance, then to Gradient.

XswampyX
12-01-2013, 05:22 PM
Light intensity in real world depends on inverse square law.
So the farther from light source, the less photons is colliding with object.
Simply plug Item Info World Position and Spot Info World Position to Math Vector Distance, then to Gradient.

Like so....

http://i465.photobucket.com/albums/rr16/xXswampyXx/Lamp_Var_Col_zps39a6d9cf.jpg (http://s465.photobucket.com/user/xXswampyXx/media/Lamp_Var_Col_zps39a6d9cf.jpg.html)

Rove
12-01-2013, 05:42 PM
awesome! thnx for the swift reply.

XswampyX
12-01-2013, 05:51 PM
That's quite an acute observation on how a lampshade behaves, not something I would have though of. :thumbsup:

Sensei
12-01-2013, 06:26 PM
Copy from mine post to quantum physics forum:

Intensity is quantity of photons per area. Very large quantity.

The further from source emitting photons (or other particles), particles are spread on larger area.

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/imgfor/isq.gif

If you have 100 W light bulb, and it's emitting light at 525 nm wavelength, each photon has E=h*c/525nm =3.786e-19 J

100 W = 100 J/s (let's forget about loses)

100 J/3.786e-19 J=2.641*10^20 photons in the all directions, per second.



1 m from light bulb quantity of photons is 2.641*10^20 / 4*PI*1^2 = 2.1*10^19 per second per 1m^2

2 m from light bulb quantity of photons is 2.641*10^20 / 4*PI*2^2 = 5.254*10^18

3 m from light bulb quantity of photons is 2.641*10^20 / 4*PI*3^2 = 2.33*10^18

1000 m from light bulb quantity of photons is 2.641*10^20 / 4*PI*1000^2 = 2.1*10^13

We can go further and there will be distance with 1 photon per 1 m^2 per second

And further there will be gaps without any photons in unit of area.



Quantization of energy is essential to not have absurds/paradox like infinite energy.

More about inverse-square law:
http://en.wikipedia.org/wiki/Inverse-square_law
http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

Sensei
12-01-2013, 06:30 PM
That's quite an acute observation on how a lampshade behaves, not something I would have though of. :thumbsup:

But the further from light source, photon has exactly the same frequency and wavelength as it had in the center. Color doesn't change with distance.

Rove
12-01-2013, 07:10 PM
damn that's to tech for me. But I'm sure glad you know your stuff cuz in the end my ricepaper lamp will look exactly how I want it to look. Thnx a bunch!

JoePoe
12-01-2013, 10:28 PM
But the further from light source, photon has exactly the same frequency and wavelength as it had in the center. Color doesn't change with distance.

Thank you. Yes!
The only thing hat would change color ove distance would be atmospheric interference. i.e. pollution etc.

spherical
12-01-2013, 10:55 PM
Well, possibly due to a language difference (because the first sentence didn't really make sense), I read the question a different way. I took it to mean a blackbody radiation curve; something I have been dealing with in LED specifications for one of our light fixtures. The lower the "intensity" (brightness value) the warmer the radiation appears—as in an incandescent or halogen variant that goes from fairly neutral white at 100% to orange as it is dimmed; eventually approaching the wavelength of a candle flame.

Sensei
12-02-2013, 12:00 AM
White color is range of photons with wavelengths between 400 nm (purple color) to 700 nm (red color).
Colorful LED, or lasers, are emitting light at one wavelength +- 10 nm f.e. (or other tolerance).
When source will emit light at range of wavelengths, it's no so easy to calculate energy used to emit them as showed in #6 post, nor its intensity.
Instead there are simply used Watts. Or Joules (kWh = 3.6 MJ).
This way we don't have to get into detail about frequencies/wavelengths of device.

Incandescent light bulb is emitting light at full range of photons, so it's appearing white.
But when we will connect it to VAC through rectifying diode, it won't be white anymore.
It will show reddish-orange color.

spherical
12-02-2013, 03:23 AM
Colorful LED, or lasers, are emitting light at one wavelength +- 10 nm f.e. (or other tolerance).

Actually, there are LEDs that have a tunable Coordinated Color Temperature that follow the Blackbody Curve, so they do not stay the same wavelength throughout their brightness range.


Incandescent light bulb is emitting light at full range of photons, so it's appearing white.
But when we will connect it to VAC through rectifying diode, it won't be white anymore.
It will show reddish-orange color.

Yes. As the voltage drops, the element cools and the color temperature value decreases into red end of the spectrum.

XswampyX
12-02-2013, 10:45 AM
But the further from light source, photon has exactly the same frequency and wavelength as it had in the center. Color doesn't change with distance.

I agree, but we are dealing with the colour of the light as it travels through the lamp shade not the air. It's more of a dirty hack. :)