why does fire create light ?

Fire is an intense chemical and oxidation reaction.

This reaction is highly exothermic and produces lots of energy.

The energy that is released in the IR (infrared radiation) portion of the electromagnetic spectrum that we can feel is called heat.

The energy that is released in the visible portion of the EM spectrum that we can actually see, we generally call light.

Fire creates lots of heat, and that means molecules are moving rapidly. They collide with each other, knocking their electrons into high-energy states. As the electrons decay back to their default energy level, they emit photons (light particles). The greater the jump back down the the default energy level, the higher the frequency of the emitted photon.

The frequency of a photon is perceived as color, with red light having the lowest frequency, and violet light having the highest (among the visible part of the spectrum).

A flame is a mixture of reacting gases and solids emitting visible and infrared light, the frequency spectrum of which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide.

The glow of a flame is complex. Black-body radiation is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also photon emission by de-excited atoms and molecules in the gases. Much of the radiation is emitted in the visible and infrared bands. The color depends on temperature for the black-body radiation, and on chemical makeup for the emission spectra. The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke.

The National Aeronautics and Space Administration (NASA) of the United States has recently found that gravity plays a role. Modifying the gravity causes different flame types.[3] The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a general flame, as in a candle in normal gravity conditions, making it yellow. In micro gravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although it may go out if not moved steadily, as the CO2 from combustion does not disperse as readily in micro gravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs.[4] Experiments by NASA reveal that diffusion flames in micro gravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behave differently in micro gravity when compared to normal gravity conditions.[5] These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.

Fire is rapid oxidation of a substance. Oxidation is the lose of electron. The lost electron will scatter out and into our eyes as light. Works same was as a television which is an electron gun that shoots electrons to our eyes.

fire (heat) is infrared radiation.

The light that you see, is the color your eye perceives is what is being reflected off of the fire.

Same answer as to why the sky is blue (just a different radiation, (scattered))