Six Ways of Looking at a Bulb
Field notes from an unplanned spectroscopy experiment, conducted in a bathroom.
I have a confession. The diffraction grating I have built my entire art practice on is, by most measures, the wrong tool for the job. It is a piece of cheap plastic with too few lines per millimeter to do real science, and it has been broken and reassembled imperfectly. It's also one of the most important objects I own.
A few weeks ago, I decided to expand the toolkit. I ordered a small variety pack of gratings in different line counts — 50, 80, 100 (a fresh, unbroken one), 300, and 600 lines per millimeter — and waited for them to arrive. Yesterday, I lined them all up and pointed them at the same bathroom bulb. The bulb in question is not arbitrary, this is the bulb from The Yellow I've Been Chasing. This is the bulb that finally gave me back a specific shade of yellow I had been searching for since one school-run sunrise over a decade ago. I wanted to know what each grating would do with the same source.
This is what I found.
A quick word on what these tools actually are.
A diffraction grating is a piece of material with extremely fine parallel lines etched into its surface. When light passes through the grating, each line acts as a tiny obstacle that bends the light slightly, and the bent paths interfere with each other to separate the light into its component colors. The number of lines per millimeter controls how much the light spreads. More lines, more spread. Fewer lines, less spread.
Outside of art, these are scientific instruments. Diffraction gratings are used in spectroscopy — the practice of measuring the spectrum of a light source to figure out what it contains. Astronomers use them to identify the elements in stars. Chemists use them to identify unknown compounds. Physics teachers use the cheap ones to show students that white light is actually a stack of rainbows in disguise.
I am not a scientist. I am a researcher, maintaining my amateur status so I can research in the Olympics. And now, strangely - an artist. The gratings don't really care, there happy to spread light the same way regardless of whether I want to measure a star or photograph a sunrise.
The control: my original broken 100 l/mm grating.
This is the tool that built the practice. A 100 lines per millimeter plastic grating that arrived from a late night "add to cart", broke at some point in my hands, and was reassembled imperfectly. Every micro-fracture in the plastic acts as its own tiny additional grating, with its own slightly different behavior. The result is that the broken grating is no longer one instrument, but dozens stacked on top of each other.
When I photograph through it, I get all of the spectral behaviors at once — soft warmth, layered ring halos, discrete rainbow accents, atmospheric color spread. The broken grating is a symphony. The new gratings, as I would discover, are each playing a single instrument.
50 lines per millimeter.
Officially, the lowest line counts are used for demonstration and teaching — they are the gratings handed to physics students to show what spectral separation looks like at the simplest level. They spread light a small amount and leave most of the original color intact.
What this means in practice: the 50 barely splits the light at all. What it does instead is bathe everything in the source color. When I pointed it at the bathroom bulb, the entire frame turned warm gold. The walls, the shade, the reflection, all gold. The rainbow effect is reduced to a small accent at the bulb's edge. The grating did almost nothing, and in doing almost nothing, it gave me the closest photograph yet to what the school-run sunrise actually felt like — a single warm color filling the entire field of view.
80 lines per millimeter.
The 80 is an unusual line count, mostly found in educational kits between the 50 and the 100. It doesn't really have a strong professional use case. It exists in the middle of "let's see what this can do" and "let's put this to use."
In practice, the 80 turned out to be the most surprising grating in the set. The bulb dominates the frame, the rainbows are reduced to small crisp bridges at the edges of the light, and the entire scene is bathed in a soft gold — even more than the 50, because the 80 spreads the light slightly more without breaking the dominance of the original color. If the 50 is the sunrise, the 80 is the room after the sunrise — every surface still holding the warmth.
The 80 is going to be a quiet specialist. I will reach for it when I want temperature without drama.
100 lines per millimeter (new, unbroken).
The 100 is the entry-level tool for hobbyist astronomical spectroscopy. With one of these mounted in front of a telescope, you can capture the spectrum of bright stars, identify major absorption lines, and start to see why a hot blue star looks different from a cool red one. (This is why I originally bought one.) 100 l/mm is the line count at which a grating becomes useful for measuring rather than merely demonstrating.
I bought a new 100 specifically to compare against my broken one. I wanted to know what the break was doing — whether it was making the grating worse, better, or just different.
The new 100 is clean. It produced a soft pillar of pastel light running through the center of the frame — pinks, peaches, mints, lavenders — like an aurora rather than a rainbow. The colors are gentler than the broken grating's output. The composition is more architectural, almost mandala-like. The new 100 makes meditative light.
This is beautiful, but it's also not my voice. Side by side with the broken grating, the difference is unmistakable.
100 lines per millimeter (broken, original).
Same line count. Same plastic. Same intended behavior. Completely different result.
The broken grating produced the photograph I would describe as the complete sensory event — the bulb at the center, surrounded by expanding concentric rings of orange, yellow, peach, mint, and lavender, with discrete rainbow accents threading through them. The new 100's pastel pillar is also here, but so is the 50's warmth, and the 300's saturation, and a hint of the 600's spectral edge banding. All at once.
This is what the break is doing, layering the light. The result is a photograph that looks less like a spectrum and more like a morning — many related colors stacked together, with one dominant note.
The broken grating is irreplaceable. I have empirical proof of this now.
300 lines per millimeter.
The 300 is the line count at which gratings cross from demonstration into real scientific measurement. These are used in undergraduate physics labs, industrial light-quality testing, and serious amateur astronomy. At 300 l/mm, you can begin to resolve specific absorption lines in stellar spectra — including the Fraunhofer lines in sunlight, the dark bands that reveal what elements are present in the sun's atmosphere.
In artistic practice, the 300 is kinetic. Pointed at the same bulb, it produced a centered composition with a full spectral halo above and below the light, like an altar. When I rotated the grating to a diagonal, the entire frame turned into a constellation — the central bulb as a small sun, four spectral teardrops orbiting around it, the diagonal rainbow streaks pulling the eye upward and to the right in the direction of a rising sun.
The 300 is going to be the grating for movement, for ecstasy, for being inside a moment of light rather than observing it from outside.
600 lines per millimeter.
The 600 is approaching professional spectroscopy territory. It is used in commercial spectrometers, fluorescence detectors, lower-end Raman spectroscopy systems, and serious astronomical work. At 600 l/mm, individual emission lines from gas discharge lamps become resolvable — you can identify hydrogen, helium, neon, and mercury by the pattern of their spectral signatures.
In practice, the 600 turned this bathroom bulb into a scientific reference plate. The spectrum was spread vertically into discrete, stacked bands of color — clean blue at the top, green, yellow, orange, red at the bottom — with the original bulb visible at the top of the frame and its entire spectrum unzipped below it like a chemical signature.
The 600 is the grating that produces data. When I point it at a tungsten bulb, I get a continuous rainbow because tungsten emits across all visible wavelengths. When I eventually point it at a firefly — a creature whose bioluminescence is a narrow biochemical emission peaked in the yellow-green — I expect to see a single saturated band with empty space above and below it. That photograph will be both art and proof, simultaneously.
What the experiment taught me.
Six gratings vs one bulb. Six completely different photographs. Each grating did exactly what its physics dictated, and each one produced a different emotional register:
50 l/mm → warmth
80 l/mm → temperature
100 l/mm broken → the morning, complete
100 l/mm new → stillness, aurora
300 l/mm → movement, kinetic spectrum
600 l/mm → analytical, scientific
I went into this experiment thinking I was buying backup gratings for the practice and I came out of it with an entire expanded vocabulary. Each line count is now a different paint color in the kit. The broken 100 is still the voice but the others are tools that extend the range.
I also confirmed something I have suspected for a while. The broken grating is accidentally perfect for this job. Every micro-fracture in it is unique. There is no replacement, only successors. When the original eventually fails completely, I will move forward with one of the new ones, and the work will change. Until then, I will keep using the broken one as my primary instrument, and use the others when I want a different mood.
That is what an afternoon with six pieces of plastic can teach an artist about her own medium.
— Cassie