Key Difference: When the light falls on any surface, a part of that light is sent back to the same medium. This is known as reflection. Light is deflected; means it bounces back on the plane surface when it is bent by a gravitational force.

According to the Dictionary.com, Reflection is:

• The act of reflecting or the state of being reflected.
• An image; representation; counterpart.
• A fixing of the thoughts on something; careful consideration.
• A thought occurring in consideration or meditation.
• An unfavorable remark or observation.

When the light falls on any surface, a part of that light is sent back to the same medium. This is known as reflection. The angle of occurrence and angle of reflection are the same in the case of reflection. The light beam that leaves the surface is called the reflected ray. It merely deals with light and sound, whereas, the deflection deals with mass and velocity (energy and work). Deflection also deals with sound and light, in this the main focus is on light waves. There are two types of reflection: Specular Reflection and Diffuse Reflection.

Specular reflection is the light that is reflected in the same angle. Whereas, in the diffuse reflection, the light reflected from the rough surface is scattered in all direction. It does have the consistency, or it is not angled in the same direction like specular reflection.

According to the Dictionary.com, Deflection is:

• The act or state of deflecting or the state of being deflected.
• Amount of deviation.
• The deviation of the indicator of an instrument from the position taken as zero.

Light is deflected; means it bounces back on the plane surface when it is bent by a gravitational force. For example, a mirror never reflects the exact sum of light; and it will bounce back on the other side. If a ball is hit on the ground, it will never bounce back to the same spot where it first started. The Law of Thermodynamics states that in deflection that there is a relation to energy and work. The corpuscular theory of light states that the reflection of light helps the deflection of small light particles (corpuscles). The deflections of waves like light consist of reflection and refraction.

Comparison between Reflection and Deflection:

Image Courtesy: micro.magnet.fsu.ed, blog.cencophysics.com