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Field Notes

1 logged

Observations logged by the lab and the people who keep this specimen — where it lives, what light moves it, what it does that we didn’t expect.

  1. № 001Tao Science LabsThe LabJun 9, 2026

    The one we wear gloves for

    We took the first sheet out back with a scrap of pine. It smoked before the stopwatch was going, and burned a hole clean through the board a moment later.

    Here's the strange part: nothing is added. That sunlight is already landing on your arm. The sheet only gathers a plate-sized helping of it into one spot — roughly ten thousand times the daylight around it. Same sun, folded.

    Fresnel did the folding in 1822. Glass only bends light where it curves, so he threw the thick middle away and kept the curve, pressed flat into rings — lighthouses got it first. Ours is 400 mm across with its focus 240 mm out: nearer than the sheet is wide.

    An eye would be hurt permanently in milliseconds, and the acrylic itself softens above about 160 °C — it isn't immune to what it does. Gloves on, clear day, nobody downrange. Then log yours below.

№ 002 · Unlogged

The log is open. This entry belongs to whoever keeps this specimen next.

Specimen Record

Spec Sheet

Aperture
400
mm
Focal length
240
mm
f-number
f / 0.6
Profile
Positive Fresnel
Substrate
PMMA
Optical acrylic
Refractive index
1.49
Visible spectrum
Design origin
A.-J. Fresnel
France · 1822
Mass
1020
grams

Handling & Safety

Concentrated sunlight at this lens's focal point reaches irradiance on the order of 10⁴× the ambient solar background. This is sufficient to ignite paper, char wood, soften metal, and cause permanent retinal damage in milliseconds.

Eyes
Never look at or near the focal spot under sunlight. Wear ANSI Z87.1+ eye protection rated for visible light when operating. Welder's shade 5 or higher is recommended for prolonged use.
Hands & skin
The focal point will burn through skin instantly. Treat it as you would an active torch.
Flammables
Keep dry leaves, paper, fabric, fuel, and other ignition-sensitive material at least 1 m from the lens when in sunlight. The PMMA substrate itself is flammable above ~160 °C and will deform or burn if the focal spot reflects back onto the lens.
Surface
Use on non-flammable, heat-tolerant work surfaces. Concrete, ceramic, and steel are appropriate. A solar lens of this size will turn a wooden table into a small forge.