Diamond Light Return Score Calculator – Turning Proportions Into Performance
The Diamond Light Return Score Calculator on MyTimeCalculator transforms the technical numbers from a diamond report into intuitive scores for light return, fire, scintillation and overall cut performance. Instead of memorizing ideal ranges and trying to combine them in your head, you can enter table, depth, crown angle, pavilion angle, girdle, culet, polish and symmetry and see how they work together in one model.
This calculator focuses on round brilliant diamonds, where light performance is strongly driven by how well the cut is balanced. The model does not simulate ray paths inside the stone but uses a penalty-based approach: each parameter is compared to an ideal value, the deviation is converted into a penalty and the penalties are subtracted from 100 to produce final scores.
The Core Light Return Formula
The Light Return Score is designed to reflect how efficiently the diamond sends light back to the viewer. It combines the effects of table, depth, crown angle, pavilion angle, girdle, culet and finish grades into a single number between 0 and 100.
Each penalty increases as the parameter moves away from a preferred range. Small deviations create small penalties, while large deviations approach a capped maximum penalty so that extreme outliers do not push the score below zero.
How Penalties Are Built From Ideal Values
For each core proportion, the model starts with an ideal target close to common recommendations for modern round brilliant diamonds:
- Table percentage in the high 50s
- Depth percentage in the low 60s
- Crown angle in the mid-30s
- Pavilion angle a little above 40 degrees
A simple penalty function then compares measured and ideal values.
Each parameter uses its own tolerance and MaxPenalty. For example, pavilion angle might use a smaller tolerance and higher weight than table percentage because small shifts in pavilion angle can have a large impact on light leakage. Crown angle, depth and table each have their own sensitivity in the model.
Finish Penalties From Polish And Symmetry
Polish and symmetry represent how carefully the diamond was finished. Excellent finish means the cut is clean and consistent, while lower grades can indicate facet irregularities, misalignment or surface features that disturb light paths. The calculator converts these grades into numeric finish penalties that feed into all three scores.
Excellent adds almost no penalty, Very Good adds a modest amount, Good adds more and Fair or Poor add increasingly larger penalties. In the Light Return Score these penalties are present but somewhat moderated, while in the scintillation score they are weighted more heavily.
Girdle And Culet Penalties
Girdle thickness and culet size also influence light behavior and durability. A very thin girdle may be delicate and chip-prone, while a very thick girdle can hide weight and compress the useful face-up spread. A large culet can show as a visible window in the center of the stone.
CuletPenalty ≈ value based on culet size (none, very small, small, medium, large)
Medium girdles and no-to-very small culets receive the smallest penalties. As you move away from those central categories, the penalties gradually increase and reduce the light return score.
Fire And Scintillation Score Formulas
The calculator uses the same underlying penalties to build separate scores for fire and scintillation. Each score emphasizes different aspects of the geometry and finish.
Fire score
Fire is the colored light you see as spectral flashes. It is influenced by how crown height, pavilion depth and table size work together.
The weights a, b, c and d are chosen to emphasize crown angle and table percentage slightly more than pavilion and depth, with a smaller contribution from finish. Diamonds with balanced crown and table proportions and strong finish will tend to show higher fire scores.
Scintillation score
Scintillation is the pattern of bright and dark areas and the way sparkles turn on and off as the diamond moves.
Here, finish penalties from polish and symmetry are more heavily weighted, because facet precision and alignment are critical for pleasing scintillation patterns. Proportion penalties still matter, but finish quality is more prominent in this score.
Overall Cut Performance Formula
To present a single, easy-to-compare metric, the calculator combines the three component scores into an overall cut performance score.
Light return receives the largest weight because it reflects the core efficiency of the diamond’s cut. Fire and scintillation together contribute the remaining half, ensuring that the balance between white light, colored light and sparkle is still represented in the final number.
Score Bands And Qualitative Ratings
To make the numeric scores easier to interpret, the calculator also assigns a qualitative rating.
80–89 → Very Good
70–79 → Good
60–69 → Fair
0–59 → Poor
These labels are not official grades from any laboratory, but they help you quickly understand where a stone stands on a consistent scale. You can use the overall score and rating to compare two diamonds with similar color and clarity but different cut proportions.
Example: Proportions Close To Modern Ideals
Suppose you enter a table of 57%, depth of 61.5%, crown angle of 34.5° and pavilion angle of 40.8°, with a medium girdle, no culet and Excellent polish and symmetry. In this configuration, all proportion deviations are small, girdle and culet penalties are minimal and finish penalties are near zero. The calculator will produce high light return, fire and scintillation scores, and an overall performance score likely in the Excellent band.
Example: Deep Stone With Large Table And Fair Finish
Now imagine a diamond with a 64% table, 64% depth, a shallow crown angle and a too-steep pavilion angle, combined with a thick girdle and Fair polish and symmetry. Each of these inputs pushes its penalty higher. The sum of proportion penalties and finish penalties significantly reduces all three scores. The overall cut performance value falls into the lower bands, reflecting potential light leakage, weaker fire and less pleasing scintillation.
How To Use The Diamond Light Return Score Calculator
- Locate the table percentage, depth percentage, crown angle, pavilion angle, girdle description, culet size and polish and symmetry grades on your round brilliant report.
- Enter each value in the corresponding input fields of the calculator.
- Click the calculate button to generate light return, fire, scintillation and overall performance scores.
- Review the numeric scores and the overall rating label to understand how the stone performs from a cut perspective.
- Compare multiple stones by repeating the process and recording their scores side by side.
Diamond Light Return FAQs
Frequently Asked Questions About Light Return And Cut Performance
Understand how proportions and finish grades affect diamond light return, fire and scintillation so you can interpret your calculator results with confidence.
Pavilion angle strongly influences whether light reflects back through the crown or leaks out the bottom. The model uses a tighter tolerance and higher weighting for pavilion angle, so even small deviations from the ideal can produce noticeable penalty changes and affect light return scores.
Yes, if the proportions are very strong. Good polish introduces a moderate finish penalty, but excellent proportions can still yield high scores. However, polish and symmetry become more important in the fire and scintillation scores, where facet precision and surface quality matter more to the sparkle pattern.
The current version focuses on internal light performance rather than face-up spread. Depth and table percentage indirectly influence spread, but the score model is tuned to interpret their impact on brightness, fire and scintillation rather than millimeter size alone.
Yes. The light performance of a round brilliant diamond is driven by geometry, not by whether it is natural or lab-grown. As long as you have accurate proportion and finish data, the same formulas and scores apply to both categories.
Some grading reports show only basic percentages. For the most informative results, you need crown and pavilion angles. If your current report lacks them, you can request additional data or look for stones with full proportion information so the calculator can evaluate light performance more accurately.