Category: fluorescent lamps

What is zero point energy? — AWG, Karachi, Pakistan

All objects in our universe have wave-like characteristics that manifest themselves in certain circumstances. These wave-like characteristics become more significant as objects become smaller. Their wave-like characteristics allow small particles to have ill-defined locations. To understand what I mean by “ill-defined locations”, consider a wave on the surface of a lake. There is no one point at which this wave is located—it is located over a region of the water’s surface. Waves don’t have well defined locations. Similarly, if you observe an electron, which is really a wave, there is no one point at which that electron is located—it is located over a region of space. Because of the detailed relationships between wavelength, frequency, and energy, the smaller the region of space in which the electron-wave can be found, the higher its energy must be. Thus an electron that is localized at all—that is known to be within a certain region of space—must have a certain minimum energy, even if it is stationary. This minimum energy is called zero point energy and it is a consequence of trying to localize the particle within a certain region of space. Since the zero point energy is a base level and can’t be reduced, you can’t use zero point energy to do anything useful. It’s just there.

Does food coloring change the color of food?

Food coloring is a solution of dye molecules—molecules that absorb light of certain wavelengths extremely efficiently. When a particle of light—a photon—of the right wavelength encounters one of these dye molecules, an electron in the molecule uses the photon’s energy to shift from one quantum level to another. The photon vanishes and the molecule is placed in an electronically excited state. The dye molecule’s electron quickly returns to its original quantum level by releasing this extra energy as thermal energy within the molecule and its surroundings. Overall, the photon has vanished and the dye has become warmer. When you add these dye molecules to food, the dye gives the food a color by preventing that food from transmitting or reflecting certain colors of light. The dye simply absorbs those colors.

Is there an effective shield for the EMF generated from mercury vapor ballasts? — CS, Washington, DC

An electric field can always been shielded by encasing its source in a grounded conducting shell. Electrically charged particles in the shell will naturally rearrange themselves in such a way as to cancel the electric fields outside the shell. But magnetic fields are harder to shield, particularly if they don’t change very rapidly with time. The difficulty with shielding magnetic fields comes from the apparent absence of isolated magnetic poles in our universe—there is no equivalent of electrically charged particles in the case of magnetism. As a result, the only way to shield magnetic fields is to take advantage of the connections between electric and magnetic fields.

Because changing magnetic fields are always accompanied by electric fields, the two can be reflected as a pair by highly conducting surfaces or absorbed by poorly conducting surfaces. In these cases, the electric fields push and pull on electric charges in the surfaces and it is through these electric fields that the magnetic fields are reflected or absorbed. However, this effect works much better at high frequencies than at low frequencies, where very thick materials are required. Appliances that operate from the AC power line have magnetic fields that change rather slowly with time (only 120 reversals per second or 60 full cycles of reversal each second) and that are extremely hard to shield with conducting material. Instead, their magnetic fields have to be trapped in special magnetic materials that draw in magnetic flux lines and keep them from emerging into the surrounding space. One of the most effective magnetic shield materials is called “mu metal”, a nickel alloy that’s like a sponge for magnetic flux lines. Since it also conducts electricity pretty well, it is an effective shield for electric fields. So if you wrap your mercury vapor ballasts in mu metal, there would be almost no electric or magnetic fields detectable outside of the mu metal surface.

There is a debate amongst the teachers in our school as to what are the three primary colors. Some say Red, Green, and Blue, others say Red, Yellow, and Blue. Do you have an explanation? — RS, Farmington Hills, MI

The true primary colors of light are Red, Green, and Blue. This empirical result is determined by physiological characteristics of the three types of color sensitive cells in our eyes. These cells are known as cone cells and are most sensitive to red light, green light, and blue light respectively. Light that falls in between those wavelength ranges stimulate the three groups of cells to various extents and our brains use their relative stimulations to assign a color to the light we’re seeing. For example, when you look at yellow light, the red sensitive and green sensitive cone cells are stimulated about equally and your brain interprets this result as yellow. When you look at an equal mixture of red light and green light, the red sensitive and green sensitive cells are again stimulated about equally and your brain again interprets this result as yellow. Thus you can’t tell the difference between true yellow light and an equal mixture of red light and green light. That’s how a television tricks your eyes into seeing all colors. If you look closely at a color television screen, you’ll see tiny dots of red, green, and blue light. But when you back up, you begin to see a broad range of colors. The television is mixing the three primary colors of light to make you see all the other colors.

Incidentally, the three primary colors of pigment are yellow, cyan, and magenta. Yellow pigment absorbs blue light, cyan pigment absorbs red light, and magenta pigment absorbs green light. When exposed to white light, a mixture of these three pigments controls the mixture of the reflected lights (red, green, and blue) and thus can make you see any possible color.

I have experimented with passing high voltage arcs through ionic compounds and have observed different colors when I do. An arc through salt (sodium chloride) produces a brilliant yellow light. How does this work? — JB, Lantana, FL

When electric current passes through air as an arc, the air becomes hot enough to vaporize the compounds you expose to it. As a result, there are individual sodium and chlorine atoms moving about in the arc itself. Like all atoms, a sodium atom resembles a tiny planetary system. It has 11 negatively charged electrons orbiting a massive, positively charged nucleus. But unlike our experience with the solar system, the electrons in a sodium atom can only travel in certain allowed orbits or “orbitals.” These electrons are normally found in the orbitals with the lowest possible energy. But when charged particles in the arc collide with sodium atoms, they often shift electrons in those atoms to orbitals with more energy. The electrons quickly return to their original orbits and emit their excess energies as light during their returns. In the case of sodium, the final step of the most common return path results in the emission of yellow light with a wavelength of about 590 nanometers. This yellow light is the same one you see in the sodium vapor lamps that are used to light highways and parking lots.

While sodium tends to emit yellow light, other atoms have different orbital structures and emit their own characteristic colors. Copper and barium atoms emit blue/green light while strontium atoms emit red light. These colored lights are the same ones that you see in fireworks.

How does luminol work? — CW, San Antonio, TX

Luminol produces light during a chemical reaction with either molecular oxygen or a mixture of potassium ferricyanide and hydrogen peroxide and is probably the basis for most light sticks. In an alkaline (basic) solution, the luminol molecule becomes a dianion, a molecule with two negative charges on it. In this dianion form, the molecule has two nitrogen atoms exposed to the solution and these nitrogen atoms are easily replaced by two oxygen atoms. When that exchange takes place, a molecule of nitrogen gas is released and the final oxidized luminol is left in an electronically excited state. This molecule quickly gets rid of its excess energy by emitting light.

What causes things to glow in the dark? Why does phosphorus glow? Why does the glow die? — DB & EB

Most glow-in-the-dark materials store energy when they are exposed to visible light and then glow dimly as this stored energy is gradually converted back into light. In such a material, exposure to light promotes some of the electrons in the atoms or molecules to excited states and these electrons become trapped in lower-energy excited states from which they have trouble escaping. It takes a very long time for each of these trapped electrons to return to their original states by emitting light. Since that return is a random process, a glow-in-the-dark object glows with an ever diminishing light as the excited electrons return at random moments to their original states. Eventually almost all the electrons have returned and the glow weakens to essentially nothing.

White phosphorus also glows in the dark, but not for the same reason. You don’t need to expose white phosphorus to light to make it glow; you need to expose it to air. The chemical reaction between phosphorus and oxygen causes the phosphorus to emit light. This reaction can also cause the white phosphorus to burst into flames. Because of its dangerous flammability and its toxicity, white phosphorus isn’t something you want to have around.

How do neon lamps work? — TF, Auburn, WA

A neon lamp consists of a neon-filled tube with an electrode (a metal wire) at each end. When you put enough electrons on one of the electrodes and remove enough electrons from the other, electrons will begin to leap off the first electrode and accelerate toward the other electrode. Because the density of neon atoms in the tube is relatively low, only about 1/1000th that of air molecules in normal air, the electrons can travel long distances without colliding with a neon atom. As the electrons accelerate, their kinetic energies increase. However, these electrons occasionally collide with neon atoms and, when they do, they can give up some of their kinetic energies to those atoms. The neon atoms then end up with excess energy and they often emit this energy as light. The color of this light is determined by the structure of a neon atom and tends to be the familiar red of a neon sign.

What are the two chemical in glow sticks? — JW, Westport, CT

I believe that the glow sticks contain luminol and hydrogen peroxide, which mix when you crack the glass ampoule and begin to emit light. There are several other chemicals present in the sticks to assist and control the process, but the principal reaction is one in which the hydrogen peroxide oxidizes (“burns”) the luminol molecule. The result is a product molecule that is initially in an excited state—its electrons have more energy than they need—and it emits a particle of bluish-violet light. Since our eyes aren’t particularly sensitive to that bluish-violet light, it’s often converted into more visible light with the help of a fluorescent dye. The green light sticks probably contain sodium fluorescein molecules, each of which can absorb a photon of bluish-violet light and reemit some of its energy as a photon of green light. Other dyes, probably rhodamines, are used to make red or orange light sticks.

I have seen some new 48″ fluorescent tubes rated at 25W compared to the standard 40W. I was told I could use these in my existing fixtures without doing anything to the ballast. What effect will replacing a 40W bulb with these 25W bulbs have on my fixtures and ballasts? – ST

I would guess that the lower wattage tubes will work fine in your existing fixtures, but I am not expert enough to be certain. The 25W tube itself is evidently built so that a smaller current flows through it than through a normal 40W tubes when the two are exposed to similar voltages. The ballast’s job is to prevent a catastrophic rise in that current by adjusting the voltage across the tube dynamically during each half cycle of the power line and to keep the tube operating even as a half cycle is coming to an end. Although the 25W tube will draw less current than the ballast expects, the ballast should behave pretty well. I would expect that the tube designers have anticipated this situation and have built the tube to operate with the standard ballast. If a reader knows better, please let me know.