2. Is Light continuous or discrete?

How do we define Light in simple words?

1. Light is an outcome of rays that originated from Sun.
2. It can penetrate through objects which have less opacity.
3. It can bend
4. It can get reflected.
5. It is continuous.

Are we done? I don't think so because Light is the most primary source of life in our universe and so it's characteristics can't be limited to this short basic list. All the above statements are true except that the 5th one is partially true or it's not always the case! So, when we say 'Light can be continuous' it becomes complete.

Why 'can be'? To put this clearly, Light can also be a series of discontinuous packets! Analog had always been the idea before digital was formed in every field. It was also true for Light! For centuries, Light was understood as a continuous ray emitted from Sun. In 1877, Ludwig Boltzmann's suggestion to the black body radiation problem stated that energy states of a physical system can be discrete. Eventually, the 1900 hypothesis of Max Planck about Light energy confirms the discreteness of the energy states of Light.

So, which is true? Is Light a continuous wave or discrete particles? The answer is 'both are true based on how it is observed'. To explain this further, let's see the scientific proof for this claim. It's called 'Double-slit Experiment' where light is emitted from a source and it passes through a double slit filter and it's observed on the other end on a screen. The results came out as one of major inventions in quantum physics! The test cases are as follows,

1. The slits are open -> Light creates a pattern of crossing waves on the screen proving wave like behavior!
2. The slits are open and also an apparatus is kept to observe the wave -> Light creates lines instead of the pattern of crossing waves, proving particle like behavior!

Adding an apparatus into the experiment changes the behavior of the photons! Yes, this is the base for all of the modern age theories like Cosmic/Universal Consciousness, Multiple Universes, etc. For better visual understanding of this test, I would recommend you to look at the below animated video.
http://www.youtube.com/watch?v=DfPeprQ7oGc

I would say that Light can be either wave or particles depends on the 'contributors' (We will come back on this term later!) involved in the outcome or experience. Now, let's see how we calculate the energy if light possess sometimes wave-like and sometimes particle-like behavior. If Light is treated as a wave, then we can calculate the energy from its frequency f (f=c/λ, where λ is wavelength and c is speed of Light) using the following formula. We also know that energy is proportional to the frequency and so,

E = hf, where E is energy and h is the Planck constant.

If the Light is of discrete particles, then how do we determine the frequency without wave-length? because only waves have wave-length! Yes, we can't find wave-length but definitely the frequency. The frequency is determined by the energy released by an energetic photon when it comes down from its higher energy state to the lower energy state by losing a bit of energy.

Hence, f = (E2-E1) / h, where h is the Planck constant.

So, irrespective of whether Light behaves as waves or particles, the energy E is the same and hence you can determine the missing factors using the other formula. To explore more about wave characteristics of Light, you may refer this site http://www.astronomynotes.com/light/s3.htm which I found interesting and informative!