CALCULATORS / OPTICS, IMAGING AND ILLUMINATION

LED illuminance estimate calculator

On-axis point-source illuminance using supplied luminous intensity.

optics-led-illuminance.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	illuminancelux
	25
	20

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

illuminance target25.00 lux✓ passes

BASELINE INPUTS

intensity100 cddistance2 mincidence0 deg

CALCULATED

illuminance25 lux

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# LED illuminance estimate
# Scope: On-axis point-source illuminance using supplied luminous intensity.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

intensity = 100 cd
distance = 2 m
incidence = 0 deg

illuminance := intensity*cos(incidence)/distance^2 [lux]

check illuminance target: illuminance >= 20 lux

scenario alternative: intensity = 80 cd

Calculated from your source · not saved

Baseline · Baseline

illuminance target25.00 lux ✓ passes

alternative · alternative

illuminance target20.00 lux ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

illuminance: illuminance = intensity*cos(incidence)/distance^2 [lux]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

intensity: 100 cd
distance: 2 m
incidence: 0 deg

Calculated

illuminance: 25 lux

Assumptions and limits

On-axis point-source illuminance using supplied luminous intensity.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: LED illuminance estimate. Inputs: intensity distribution; distance; angle; transmission. Outputs: illuminance; coverage. Model scope: Paraxial geometry or calibrated radiometric/photometric models. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: intensity distribution, distance, angle, transmission
Outputs: illuminance, coverage
Modes: calculate, compare, sweep
Drawing: Ray diagram and camera view

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS