# Brightness of light & light model

• wavingerwin
In summary, light exhibits wave-particle duality and all electromagnetic radiation is made of photons. The wavelength of the duality depends on the momentum of the object. The brightness of visible light is not solely dependent on the number of photons, but also on the wavelength, which affects how sensitive our eyes are to different colors. Finally, the term "brightness" has a specific definition in radiometry and may not accurately describe the concept being discussed here.

#### wavingerwin

I have been wondering
1. We know that light has a wave-particle duality. Does the "light" here mean electromagnetic radiation, or just visible lights?

2. If it EMR exhibits wave-particle duality, does that mean radio waves are transmitted in form of photons?

3. and finally, I was reading through one of the posts and quoted:
In visible light amplitude is brightness and frequency is color

Isn't the brightness in visible light dependent on the number of photons the stream of light has? (not the amplitude)

Thank you very much!

v_bachtiar said:
I have been wondering
1. We know that light has a wave-particle duality. Does the "light" here mean electromagnetic radiation, or just visible lights?
All electromagnetic radiation is made of photons, either small high energy ones in x-rays or long low energy ones in radio waves.

In fact all matter has a wave-particle duality it's just that the wavelength depends on the momentum of the object. For real world objects like a tennis ball the momentum is large enough that the wavelength is very small - so we only see the effect with very small objects like photons and sub-atomic particles.

[/QUOTE]Isn't the brightness in visible light dependent on the number of photons the stream of light has? [/QUOTE]
It depends on the number of photons/sec. However brightness for something seen by your eye also depends on the wavelength since your eye is more sensitive to certain wavelengths (colors).

Since the brightness is dependent of the number of photons per sec

So the amplitude of the wave doesn't do anything?

Photon number is non-conserved, so connecting the number of photons to the field amplitude is non-trivial. "Brightness", in addition, has a specific definition in radiometry that is different from how the term is being used here. "Intensity" or would be a better term.

## 1. What is the relationship between the brightness of light and its intensity?

The brightness of light is directly proportional to its intensity. This means that the higher the intensity of light, the brighter it will appear.

## 2. How is light modelled in physics?

In physics, light is modelled as an electromagnetic wave. This model explains the dual nature of light as both a particle and a wave.

## 3. What factors affect the brightness of light?

The brightness of light can be affected by several factors such as the distance between the light source and the object, the intensity of the light source, and the reflectivity of the object.

## 4. How is the brightness of light measured?

The brightness of light is measured in units called lumens. This unit measures the amount of visible light emitted by a source in all directions.

## 5. Can the brightness of light be changed?

Yes, the brightness of light can be changed by altering the intensity of the light source or by manipulating the distance between the light source and the object. The reflectivity of the object can also affect the perceived brightness of light.