Point a spectroscope at the fluorescent tube in your kitchen and you see a handful of bright, sharp colored lines floating on a faint background. Point it at an old incandescent bulb and you see a smooth, unbroken rainbow. Point it at a white LED and you get a rainbow with a suspicious gap and a blue spike. Same white light to your eye — three radically different fingerprints. Once you have seen that, you cannot unsee it, and you understand instantly that "white" is not one thing.
A spectroscope splits light into its component wavelengths so you can read what a source is actually made of. Here are six experiments, roughly in order of difficulty, that you can do this week with a handheld diffraction grating spectroscope.
1. The three-bulb showdown
Look at an incandescent bulb, a fluorescent tube, and an LED in turn. The incandescent gives a continuous spectrum — it's a hot glowing filament, a near-blackbody radiator, so it emits every wavelength smoothly. The fluorescent shows discrete emission lines, because excited mercury vapor inside emits specific wavelengths, and a phosphor coating fills in the rest. The LED shows a blue peak plus a broad yellow hump from its phosphor. You have just learned the difference between thermal emission and quantized atomic emission in about ninety seconds.
2. Emission lines of different gases
If you can safely view a neon sign, a sodium street lamp, or a mercury lamp, do it. Neon gives a forest of red-orange lines. Sodium gives the famous intense yellow doublet — the same yellow that makes highway lighting look monochrome. Each gas has a unique line pattern set by its atomic energy levels. This is the foundation of how we identify elements anywhere in the universe.
3. Absorption through colored glass or filters
Look at a continuous source (the sky on a bright day, or an incandescent bulb) through a piece of colored glass or a gel filter. Notice that the filter doesn't add color — it subtracts it. A red filter shows you a rainbow with the greens and blues bitten out. You are watching absorption: the dye absorbs certain wavelengths and passes the rest. This is the mirror image of emission.
4. A hydrogen lamp, if you can get one
If you have access to a hydrogen discharge tube (common in school labs), this is the holy grail. You'll see the Balmer series: a red line, a blue-green line, and a violet line. Those exact wavelengths are what Balmer fit with a simple formula in 1885, and what Bohr explained in 1913 with quantized electron orbits. You are looking at the experimental data that launched quantum mechanics.
5. Sunlight versus artificial light
Look at the daytime sky (never directly at the sun) through the spectroscope. The solar spectrum is continuous but crossed by thin dark lines — the Fraunhofer lines. These are wavelengths absorbed by elements in the sun's cooler outer layers and by our own atmosphere. The strong pair in the yellow is sodium; there are lines from hydrogen, calcium, iron, and more. Compare that to the clean line spectrum of a fluorescent tube and the difference between a star and a lamp becomes obvious.
6. Identify an unknown source
Now play detective. Point the spectroscope at a light you don't know — a shop sign, a car headlight, a camping lantern — and classify it. Continuous rainbow? It's thermal (incandescent or flame). Discrete lines? It's a gas discharge, and you can sometimes name the gas. Rainbow with a blue spike and a gap? Almost certainly an LED. You're doing exactly what astronomers do with starlight, just at arm's length.
The reason a spectroscope is such a good first instrument is that every experiment gives an immediate, unambiguous result you can interpret yourself. There's no calibration ritual, no waiting. You look, you see structure, you reason about what makes it. For thirty dollars it's the most direct window into quantum mechanics you can buy.