What the investigation does
The essay models a single-sided row of street lights using two identical bulbs and a nine-point measurement grid. With lamp spacing held constant, sensor height and test-field width vary; background-adjusted illuminance is used to calculate average illumination and uniformity.
The measured curves are compared with inverse-square reasoning and the illumination criteria cited in the historical Hong Kong design manual. The student derives a height-to-spacing ratio of about 1:2.69 for the model, then evaluates sampling density, interpolation, scaling and the missing link between illuminance and road safety.
Why this example is worth reading
Annotated setup diagrams, a defined measurement grid and explicit control of lamp spacing make the experimental design easy to follow.
The analysis considers both average illuminance and minimum-to-average uniformity, so the proposed optimum addresses more than one criterion.
Disagreement between the simple prediction and observed results becomes a reason to examine incidence angle and revise the physical explanation.
What the examiner highlights
The examiner praises the clear organization, defined photometric quantities, sound method and effective use of theory, diagrams and graphs.
The commentary recommends four or five bulbs and evidence linking illuminance to visibility, rather than assuming that relationship.
The examiner identifies uncertainty and unit-formatting weaknesses and inaccurate use of inverse and exponential terminology, while praising care and imagination in data collection.
What to examine critically
The examiner recommends more than two bulbs to represent neighboring light contributions. Nine sampling positions and interpolated curves also limit how precisely an optimum can be located.
The examiner flags uncertainty inconsistencies and confusion between inverse and exponential relationships. The historical spacing result is a model outcome, not current street-lighting or road-safety guidance.
Apply it to your own work
Define every photometric quantity before comparing models and measurements.
Use disagreement with a prediction to investigate a missing physical factor.
Separate an experimental optimum from the additional evidence needed for a practical design decision.
Essay & assessment material
Read the original material alongside the breakdown, or download it to keep.
A separate one-page examiner commentary accompanies the essay. It describes the achievement as excellent but gives no numeric mark or individual letter grade.
Source & assessment context
50 More Excellent Extended Essays (IB, 2011). The source PDFs retain their original attribution. The analysis on this page is AsterDraft’s independent teaching commentary.
Examiner-described excellent achievement; numeric mark not stated. A separate one-page examiner commentary accompanies the essay. It describes the achievement as excellent but gives no numeric mark or individual letter grade.