1. Guiding Questions for Objective 2: How are all light bulbs, (incandescent, fluorescent, halogen, and LED’s), alike in producing light? How are all of these light bulbs, (incandescent, fluorescent, halogen, and LED’s), different in their production of light? Describe how all light sources: incandescent, phosphorescent, and chemiluminescent are alike.

2. Objective 2 Terms: -escent light: incandescent, phosphorescent, & chemiluminescent chemiluminescent phosphorescent incandescent tungsten semiconductor

3. Incandescent Light Bulbs (normal bulbs with filaments) The filament in the bulb is made of the metal tungsten. Electrons (electricity) moving through the tungsten metal collide with the tungsten atoms. Electrons in tungsten atoms jump temporarily into higher orbits then jump back down, releasing photons. Gazillions of these released photons produce the light that is emitted from this light bulb. Other Information Argon gas is inside the bulb. This gas is used because if tungsten were heated to a high temperature in the presence of oxygen, it would combust (catch on fire). When the tungsten metal heats up, it releases tungsten atoms into the gas around it. When too many of the tungsten gases have been vaporized, the filament breaks and the light bulb can no longer produce light.

4. Halogen Light Bulbs Similar to an incandescent (normal) bulb: the filament in the bulb is made of the metal tungsten. Halogen bulbs produce light the same way: electrons moving through the tungsten metal collide with the tungsten atoms. The electrons in the tungsten atoms jump temporarily into higher orbits then jump back down, releasing photons. Gazillions of these released photons produce the light that is emitted from this light bulb. Difference between an incandescent bulb and a halogen bulb: in a halogen bulb the tungsten filament is surrounded by an additional glass case that is very close to the filament. The gas inside this glass bulb is a halogen gas (a group of gases – see illustration to the left). Just like in incandescent bulbs, when the tungsten metal heats up, it releases tungsten atoms into the gas around it. Unlike an incandescent bulb, when the tungsten atoms hit the halogen gas they fall back onto the tungsten and the tungsten atoms are recycled so the filament lasts longer.

5. LED Bulb (Light Emitting Diode) Instead of a metal tungsten filament in the middle of the bulb, LED’s have a semiconductor. Semiconductors are materials that allow electricity to travel through them under certain conditions but they are not made of metal. Electrons move through the semiconductor and collide with the electrons in the semiconductor. Electrons in the semiconductor jump temporarily into higher orbits then jump back down, releasing photons. Gazillions of these released photons produce the light that is emitted from this light bulb.

6. Compact Fluorescent Light (CFL) Bulbs The tube of a CFL contains liquid mercury and argon gas. The inside of the glass tubes is coated in phosphor powder. Electricity traveling through the bulb collides with the mercury atoms, the electrons in the mercury atoms temporarily jump into a higher orbit then jump back down, releasing ultraviolet (UV) photons. The UV photons collide with the electrons in the phosphor atoms causing these electrons to temporarily jump into higher orbits then jump back down, releasing photons. Gazillions of these released photons produce the light that is emitted from this light bulb.

7. Phosphorescent light Objects that glow in the dark Objects are coated in chemicals: either zinc sulphide (ZnS) or strontium aluminate (SrAl 2 O 4 ) electrons in the chemicals take longer to fall back down When all electrons have returned.- the object no longer glows

8. Chemiluminescent light emit light or glow because of a chemical reaction two chemicals are mixed together, they react, and release photons These animals generate light to confuse predators, attract a mate, lure prey, or signal their identity to others