Re: What color light bulb melts ice the fastest when shining light from bulb?

Hello Miss Jacqueline!

You asked which of the following light bulbs: clear, black (clear painted 
black), yellow, green, blue, and red might melt ice fastest by shining the 
light from the bulb on it.

OK, let's start by reviewing how a light bulb works. We have two basic 
kinds: incandescent, and fluorescent. Those are pretty scary words, but 
here's what they mean:

     a. Incandescent. Inside the bulb is little piece of tungsten wire 
called the filament. We push electric current through it, and the electrons 
that make up that current bang into the atoms of the wire and start them 
bouncing around violently. When atoms move around, we say they are hot, 
because they have a lot of energy. Eventually this energy gets to be so much 
that the atom starts to shed some of it as light you can see but much more 
of it as light you can't see called infrared light. We tend to sense 
infrared as heat because it tends to be absorbed and thus heat whatever it 
shines on. That's why an incandescent light bulb is quite hot to the touch 
and will burn you.
     b. Fluorescent. Inside the bulb is a filament, a small amount of the 
element mercury, and some nifty things called phosphors. Now, in this case, 
the filament heats up enough to vaporize the mercury and when that happens, 
the electric current now runs down the length of the bulb and causes the 
mercury to get hot. Mercury then, just like the tungsten, releases light but 
it tends to do it as another kind of light you can't see called ultraviolet.
This light strikes the phospor coatings on the inside of the glass, and they 
in turn glow with light you can see. Fluorescent lights tend to be much more 
efficient than incandescent bulbs, that is, they make more light you can see 
from a given amount of electricity.

OK, by now you should realize that the bulbs are making a lot of kinds of 
light. In fact, each bulb's filament is making almost all the colors. You 
can see this to be true by using your clear bulb and a prism; darken the 
room, and mostly cover the bulb with just a hole allowing light to shine 
into the prism. You should see a rainbow of colors on a a white piece of 
paper held where the light exits the prism. Your colored bulbs are seen to 
be red, or green, or whatever, because the glass is colored and only 
transmits some of the light made, with the rest being absorbed by either a 
coating or something mixed into the glass. 

Now we come to an important point. We have to decide just how we are going 
to control our experiment. That is, are we going to use bulbs that all have 
the same wattage (total energy used) rating? Or that produce the same amount 
of light? By the way, because your eye does not see all colors equally well, 
it may not look like equal amounts of light even if it is. That is, a yellow 
bulb producing less light will look brighter than a red bulb producing more 
light, because your eye sees yellow far easier than red.

What you need to do is look on the packaging of the light bulbs and find the 
lumen rating (i.e. the amount of light produced). Note, however, that this 
is usually rated for visible light, and thus the invisible infrared and 
ultraviolet may well skew your results!

Now, given equal amounts of light energy, we have another interesting fact. 
Water, and ice, do not absorb all colors of light equally. Usually, the red 
and yellow light are absorbed more quickly and completely than the blue. 
That's why movies made deep underwater appear to be bluish; all the red and 
yellow from sunlight at the surface has been absorbed, leaving only the blue 
light to go down deep. Thus we might expect that the red or yellow light 
will melt ice faster, IF the experiment is well-controlled so that equal 
amounts of light energy is provided of each color of light. Of course, while 
you are doing this, you have to make sure that the light is the main source 
of energy melting the ice. If this is done in a hot room, for instance, the 
general warmth of the room may overwhelm the differences from the light 
beams.

Sorry if this is sounding like it's pretty hard to run the experiment, but 
science demands a great deal of care and attention to details so that the 
results are going to mean something.  Maybe you'd like to try something of a 
different experiment that may be a little easier. Let's take a beam of 
sunlight, and break it into its different colors and use those as the light 
in our experiment. That way, we can perhaps see how much energy is in each 
color (red, orange, yellow, green, blue, violet) of sunlight, and use the 
rate of the melting of the ice as our indicator. To do this, you will want 
to put the ice into something insulated (to minimize room heat effects) and 
shine the colored beam selected from sunlight in through a small opening in 
the insulated container. You will also need a scale, so that you can always 
start with an equal amount of ice for each color of light. See if you can 
detect any difference in how long it takes for the ice to melt.