The study of heat is thermodynamics. The study of light is generally relativity but could branch into 100's of other sub categories.

A physicist 1) "The study of light, known as optics, is an important research area in modern physics." Source: http://en.wikipedia.org/wiki/Light 2) "Heat, in physics, is energy which is spontaneously flowing from an object with a high temperature to an object with a lower temperature. Heat can also refer to: In physics: Thermal energy, the sum of a body's latent and sensible forms of energy (sometimes confused with "heat") Heating, the act of increasing temperature" Source: http://en.wikipedia.org/wiki/Heat_%28disambiguation%29 3) "A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles which all ordinary matter is made (particle physics) to the behavior of the material Universe as a whole (cosmology)." "Nearly all the material a student encounters in the undergraduate physics curriculum is based on discoveries and insights of a century or more in the past. Newton’s laws of motion were formulated in the 17th century; Maxwell's equations, 19th century; and quantum mechanics, early 20th century. The undergraduate physics curriculum generally includes the following range of courses: chemistry, classical physics, astronomy, physics laboratory, electricity and magnetism, thermodynamics, optics, modern physics, quantum physics, nuclear physics, solid state physics. Undergraduate physics students must also take extensive mathematics courses (calculus, differential equations, advanced calculus), and computer science and programming. Undergraduate physics students often perform research with faculty members. Many positions, especially in research, require a doctoral degree. At the Master's level and higher, students tend to specialize in a particular field. Fields of specialization include experimental and theoretical astrophysics, atomic physics, molecular physics, biophysics, chemical physics, geophysics, material science, nuclear physics, optics, particle physics, and plasma physics. Post-doctoral experience may be required for certain positions." Source: http://en.wikipedia.org/wiki/Physicist