Glow-in-the-Dark Epoxy Sign Decay Study

ISEF Category: Chemistry

Subcategory: Materials Chemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Glow-in-the-dark signs do not just fade. They follow a timed release of stored light, like a battery emptying in slow motion. That makes them perfect for a project you can measure with a smartphone and real data. You can ask how shape, thickness, or epoxy mix changes the glow.

What Is It?

This project studies photoluminescent phosphor, a material that absorbs light and then releases it slowly. In this case, the phosphor is strontium aluminate, the same kind of powder found in many glow-in-the-dark products. When you mix it into epoxy and shape it into a lens or flat sample, you create a material that can be charged by daylight and then emit light over time.

Think of the phosphor as a crowd of tiny storage lockers. Some lockers empty fast, and some hold light longer. That is why the brightness does not drop in a simple straight line. A stretched-exponential model helps describe that uneven decay by fitting the glow curve with a math function that allows multiple release rates.

Why This Is a Good Topic

This is a strong science fair topic because you can test real material variables and measure a clear output, brightness over time. You can compare thickness, pigment loading, surface finish, or epoxy type and see how each one changes the glow curve. The project connects to emergency signage, safety lighting, and phosphor design, which gives your work a practical angle. You also get to learn imaging, calibration, curve fitting, and basic materials analysis.

Research Questions

• How does phosphor loading in epoxy affect the initial glow intensity after daylight charging? ?
• What is the effect of epoxy layer thickness on the decay rate of emitted light? ?
• Does surface finish change the measured brightness retention of phosphor-epoxy samples? ?
• To what extent does color temperature of the charging light affect the fitted stretched-exponential parameters? ?
• Which sample geometry, flat disk or curved lens, holds measurable brightness longest? ?
• How does ambient temperature change the glow decay curve of phosphor-epoxy materials? ?

Basic Materials

• Glow-in-the-dark strontium aluminate powder.
• Clear epoxy resin and hardener.
• Silicone mold or flat sample mold.
• Digital kitchen scale with 0.1 g accuracy.
• Disposable cups and stirring sticks.
• Nitrile gloves and safety glasses.
• Masking tape or black cardstock for a dark imaging setup.
• Smartphone with manual camera controls.
• Tripod or stable phone mount.
• Ruler or calipers.
• Desk lamp or sunlight charging setup.
• Computer with spreadsheet software.

Advanced Materials

• Photoluminescent strontium aluminate powder.
• Clear epoxy resin system with documented refractive index or cure properties.
• Precision balance with 0.01 g accuracy.
• Mold set for multiple thicknesses and geometries.
• Integrating sphere or calibrated light meter.
• Spectrometer or colorimeter for emission spectra.
• Dark box with fixed camera mount and controlled illumination.
• Temperature probe for sample monitoring.
• Reference luminescent standard for calibration.
• Image analysis software for intensity extraction.

Software & Tools

• ImageJ: Measures glow intensity from photos and tracks brightness changes over time.
• Python: Fits decay curves and compares stretched-exponential models across sample groups.
• Google Sheets: Organizes raw measurements, calibration data, and summary charts.
• R or RStudio: Runs statistical tests and model comparisons for decay parameters.
• Tracker: Helps align image capture timing with repeated measurements if you record video.

Experiment Steps

1. Define one material variable to test first, such as phosphor loading, thickness, or surface finish.
2. Design a way to keep charging conditions and camera settings fixed across every sample.
3. Plan a calibration method that turns photo brightness into a comparable numeric signal.
4. Choose controls that separate epoxy effects from phosphor effects and lighting artifacts.
5. Decide how you will fit the decay curve and compare models or groups.
6. Build a replication plan so you can estimate variation within each sample type.

Common Pitfalls

• Changing the phone exposure or white balance between photos, which breaks brightness comparisons across time.
• Using mixed sample thicknesses, which makes decay differences look like chemistry when geometry caused them.
• Charging samples unevenly, which creates fake differences in the first glow measurements.
• Measuring brightness in a bright room, which adds background light and flattens the decay curve.
• Ignoring sample-to-sample variation in phosphor mixing, which can hide the real effect of your design choice.

What Makes This Competitive

A competitive version of this project does more than compare which sample glows brightest. You would build a clean calibration plan, test multiple variables, and use statistics that compare whole decay curves, not just one time point. If you also link the fitted model parameters to material structure or geometry, your project starts to look like real materials research. Strong controls and repeatable imaging matter as much as the final answer.

Project Variations

• Test how different epoxy brands change glow decay when the phosphor loading stays constant.
• Compare flat films, domed lenses, and thicker cast shapes to see how geometry affects light retention.
• Use daylight, LED white light, and warm incandescent light as charging sources and compare the decay fits.

Learn More

• PubMed: Search review articles on photoluminescent phosphors, epoxy composites, and decay kinetics.
• NIH PubChem: Look up strontium aluminate and related compound properties for background on composition and safety.
• NASA NTRS: Search for papers on luminescent materials, optical coatings, and emission measurement methods.
• MIT OpenCourseWare: Find materials science and chemistry course notes that explain defects, traps, and solid-state emission.
• Journal of Luminescence: Read peer-reviewed articles on phosphor decay behavior and stretched-exponential fitting.