Canon Science Lab

Incandescent light appears yellowish compared to fluorescent light. This is because incandescent lamps produce light from heat. The filament in an incandescent lamp is what heats up. Filaments are made out of double coils of tungsten, a type of metal. Tungsten has a high electrical resistance, causing it to glow (incandesce) when an electric current flows through. Electric current, through high electrical resistance, results in heat due to the friction between the material and the electrons that are flowing through the material. Tungsten is used for incandescent bulb filaments because it is extremely resistant to melting at high temperatures. It also does not burn, because gas is injected into incandescent bulbs to eliminate all oxygen.

Fluorescent light, a common form of illumination in offices, has a more complicated light emission mechanism than incandescent light. Ultraviolet rays created within fluorescent lamps are transformed into visible light that we can see. Electrical discharge phenomena and the "excited state" and "ground state" of electrons play an important role here. Let's start with a look at the basic structure of a fluorescent lamp. Fluorescent lamps are slender glass tubes coated with fluorescent material on their inner surfaces.

Let's take a closer look at the mechanism by which fluorescent light emits ultraviolet rays. Electrons emitted from the electrode collide with the mercury atoms comprising the vapor inside the glass tube. This causes the mercury atoms to enter an excited state, in which the electrons on the outermost orbit of the atoms and molecules obtain energy, causing them to jump to a higher orbit.

The LEDs (light-emitting diodes) used in lighting emit white light similar to that of the sun. White light is created when light's three primary colors — RGB (red, green and blue) — are present. At first, there were only red and green LEDs, but the development of blue LEDs led to the development of white LEDs for use in lighting.
There are two ways to create white LEDs. The first is the "multi-chip method," in which each of the three primary-color LEDs are combined, and the second is the "one-chip method," which combines phosphor and a blue LED. The multi-chip method using three colors requires a balance between brightness and color to realize uniform illumination, and requires that each of the three color chips be equipped with a power circuit.

In our daily lives, we often notice that the color of clothing as seen under fluorescent lights indoors looks different under sunlight outdoors and that the same food appears more appetizing under incandescent lighting than it does under fluorescent lighting. Have you ever wondered what causes such differences? We see the color of an object when light strikes it and reflects back to our eyes. In short, the colors we perceive change in accordance with the wavelength component of the light source illuminating the objects we see. This results in the above-mentioned differences we perceive in clothing and food illumination.

Differences in color are represented by "color temperature." Color temperature is a numeric value representing chroma rather than the temperature of the light source. All objects emit light when heated to an extremely high temperature. Color temperature indicates what color we would see if we were to heat up an object that reflects no light whatsoever, i.e. a "black body," to a certain temperature. The unit of measurement used in this case is degrees Kelvin. Low-temperature objects appear red, and as they heat up, they start to look blue.