Lighting Brightness Calculator

This is a free photometric calculator tool to create a heatmap in terms of lux or foot-candles.

For best results, use this tool with a computer instead of a mobile device like a phone. Intructions for using the tool are below the tool itself.

How to Use the Lighting Brightness Calculator

This calculator estimates how much light reaches the calculation plane throughout a room. It combines the room dimensions, fixture layout, mounting height, lumen output, beam angle, and fixture photometry to estimate illuminance in either foot candles or lux.

For DMF fixture presets, the calculator uses manufacturer-published photometric data where available. For Custom fixtures, it uses a mathematical beam model based on the entered lumen output and beam angle.

Room Length

Enter the length of the room in feet.

For example, a room that is 18 feet long would be entered as:

18

The calculator automatically creates approximately one calculation point per foot across the room.

Room Width

Enter the width of the room in feet.

A 12 ft × 18 ft room will create an approximately 12 × 18 calculation grid across the floor or selected calculation plane.

Fixture Height Above Floor

Enter the vertical distance, in feet, from the light source to the surface where you want the lighting level calculated.

For a ceiling-mounted fixture in a 9 ft room, calculating light at the floor would normally use:

9 ft

If you are evaluating lighting at a work surface instead of the floor, use the distance from the fixture to that work surface.

For example, if the fixture is 9 ft above the floor and the work surface is 3 ft above the floor, enter approximately:

6 ft

This setting has a significant effect on the result. A fixture produces much higher illuminance when the calculation plane is closer to the light source.

Total Number of Fixtures

Enter the total number of fixtures in the room.

The calculator assumes all fixtures use the same fixture type, lumen output, and beam distribution.

Fixture Rows

Enter how many rows of fixtures are used.

The calculator automatically spaces the fixtures evenly within the room.

For example:

• 8 fixtures with 2 rows will produce approximately 4 fixtures per row.
• 9 fixtures with 3 rows will produce 3 fixtures per row.
• If the fixture count does not divide evenly between the rows, the extra fixtures are distributed among the rows.

The Fixture Layout diagram below the calculator shows the assumed fixture positions.

Lighting Application

Select the room type or lighting application that most closely matches the space.

The application selection does not change the calculated foot candles. Instead, it changes how the heat map interprets the results.

Current application presets include:

• Bedroom
• Living / Family Room
• Dining Room
• Hallway / Circulation
• Kitchen — General
• Kitchen — Work Surface
• Bathroom — General
• Bathroom — Vanity
• Home Office
• Laundry / Utility
• Custom Target

Each application has a recommended foot-candle range.

For example:

Bedroom — 10–20 fc

means the calculator treats approximately 10–20 foot candles as the recommended general lighting range for that application.

Custom Target

Select Custom Target if you want to define your own recommended lighting range.

Two additional fields will appear:

Custom Lower Target
The minimum desired foot-candle level.

Custom Upper Target
The upper end of the recommended range.

The heat map will use these values instead of one of the predefined room-type ranges.

Fixture

Choose the fixture being evaluated.

Available selections currently include:

• Custom
• DMF Artafex 4″
• DMF Artafex 2″
• DMF H Series

Selecting a DMF fixture loads manufacturer-based photometric information into the calculator.

Selecting Custom uses the entered lumen output and beam angle to estimate the fixture’s light distribution.

Distribution

For fixtures with interchangeable optics, select the desired beam distribution.

For example, the DMF Artafex 4″ includes choices such as:

• Narrow Spot — 15°
• Spot — 25°
• Flood — 40°
• Wide Flood — 60°
• General Ambient — 90°+

The Artafex 2″ includes:

• Narrow Spot — 20°
• Spot — 30°
• Flood — 40°
• Wide Flood — 50°

The degree value shown beside each distribution is the nominal beam angle.

When a distribution is selected, the Beam Angle field automatically updates to the appropriate value.

Lumen Output Per Fixture

Enter the lumen output of one fixture.

The calculator multiplies this by the number of fixtures to determine the total fixture lumens in the room.

For example:

9 fixtures × 1,000 lumens = 9,000 total lumens

When a DMF fixture is selected, a typical lumen value is automatically filled in, but the field remains editable.

This allows you to model different available lumen packages or other operating conditions without changing the fixture preset.

Beam Angle

Beam angle describes how widely the fixture distributes its light.

A smaller beam angle produces a narrower, more concentrated beam.

A larger beam angle spreads the light over a wider area.

Typical examples:

• 15° = narrow spot
• 25° = spot
• 40° = flood
• 60° = wide flood
• 90° = general ambient

Selecting a DMF distribution automatically fills this value, but it can still be manually adjusted.

For DMF presets, the calculator uses the manufacturer’s published candela distribution as the starting point. Changing the beam angle adjusts the width of that distribution.

For Custom fixtures, the beam angle is used directly by the mathematical beam model.

Brightness Units

Choose how the results are displayed:

Foot Candles (fc)
Commonly used in U.S. lighting design.

Lux
The metric unit of illuminance.

The conversion is:

1 foot candle = approximately 10.764 lux

Changing the display units does not change the underlying calculation.

Understanding the Results

Minimum

The lowest calculated illuminance anywhere in the room grid.

This is useful for identifying dark areas, typically near walls, corners, or between fixtures.

Average

The average illuminance across all calculation points.

This provides a useful overall indication of the room’s general brightness.

Maximum

The highest calculated illuminance.

This normally occurs directly below or near one of the fixtures.

Min / Avg

This is a simple uniformity measurement:

Minimum illuminance ÷ Average illuminance

A value closer to 1.00 means the lighting is more uniform.

A lower value means there is a larger difference between the darkest and average areas of the room.

For example:

• 0.80 = very even distribution
• 0.50 = noticeable variation
• 0.25 = strong bright and dark areas

This value is useful when comparing different fixture quantities, layouts, or beam angles.

Total Lumens

This shows the combined lumen output of all fixtures.

For example:

12 fixtures × 750 lumens = 9,000 lumens

Total lumens alone do not determine how bright the room will be. Mounting height, beam angle, fixture spacing, and photometric distribution all affect the actual illuminance.

Understanding the Heat Map

The heat map shows the estimated illuminance at approximately one-foot intervals throughout the room.

Each square contains the calculated foot-candle or lux value at that location.

The colors are based on the selected Lighting Application, rather than simply coloring the lowest value blue and the highest value red.

This means the colors can be meaningfully compared against the intended lighting level for the room.

Blue — Below the Recommended Range

Blue indicates that the calculated illuminance is below the selected application’s recommended minimum.

For a bedroom with a recommended range of 10–20 fc, values below 10 fc will appear blue.

Blue areas may indicate portions of the room that are relatively underlit.

Cyan and Green — Within the Recommended Range

As the lighting reaches the recommended range, the heat map moves through cyan and green.

Green generally represents the middle portion of the recommended target range.

For a bedroom set to 10–20 fc:

• Approximately 10 fc begins entering the recommended range.
• Mid-range values trend toward green.
• Values approaching 20 fc transition toward yellow.

These colors generally represent the most desirable part of the heat map.

Yellow — Upper End of the Recommended Range

Yellow represents lighting near the upper end of the recommended range.

For example, with a bedroom target of 10–20 fc, approximately 20 fc will appear around the yellow portion of the scale.

Yellow does not mean the room is necessarily too bright. It indicates that the lighting is toward the brighter end of the recommended range.

Orange — Above the Recommendation, but Not Excessively High

The calculator intentionally provides additional headroom above the recommended range.

Values above the recommended maximum transition from yellow into orange rather than immediately turning red.

This makes it easier to distinguish a slightly brighter design from one that is substantially above the intended lighting level.

The calculator provides 10 additional foot candles of headroom above the recommended maximum before displaying solid red.

For example:

Bedroom

Recommended range:

10–20 fc

Color interpretation:

• Below 10 fc = blue
• 10–20 fc = cyan → green → yellow
• 20–30 fc = yellow → orange
• 30 fc and above = red

Kitchen — General

Recommended range:

20–30 fc

Color interpretation:

• Below 20 fc = blue
• 20–30 fc = cyan → green → yellow
• 30–40 fc = yellow → orange
• 40 fc and above = red

Kitchen — Work Surface

Recommended range:

30–50 fc

Color interpretation:

• Below 30 fc = blue
• 30–50 fc = cyan → green → yellow
• 50–60 fc = yellow → orange
• 60 fc and above = red

Red — Significantly Above the Recommended Range

Red is reserved for values that are at least 10 foot candles above the application’s recommended maximum.

This does not necessarily mean the lighting is unsafe or unusable. It indicates that the area is substantially brighter than the general target used by the calculator.

Depending on the application, additional brightness may be intentional for task lighting, accent lighting, visual preference, darker finishes, or other design considerations.

Fixture Layout

The Fixture Layout diagram shows the fixture positions assumed by the calculator.

Fixtures are automatically spaced evenly according to:

• Room length
• Room width
• Total fixture quantity
• Number of fixture rows

The layout should be reviewed to make sure it reasonably represents the planned installation.

If the actual installation uses irregular fixture spacing, perimeter offsets, or fixtures concentrated around certain work areas, the calculated results will differ from the actual room.

Calculation Grid

The calculator automatically creates approximately one calculation point for every one foot of room dimension.

For example:

10 ft × 10 ft room

uses approximately:

10 × 10 = 100 calculation points

A:

15 ft × 20 ft room

uses approximately:

15 × 20 = 300 calculation points

The displayed heat-map value represents the calculated illuminance near the center of each grid area.

Important Limitations

This tool is intended for preliminary lighting design and fixture-layout comparison.

Actual lighting levels can be affected by factors including:

• Ceiling and wall reflectance
• Floor color and finish
• Furniture
• Cabinetry
• Fixture trim
• Lens or diffuser options
• Fixture aiming
• Manufacturing tolerances
• Actual installed mounting height
• LED output variation
• Room geometry
• Windows and daylight
• Other light sources in the room

The calculator does not currently model reflected light from walls, ceilings, floors, or furniture.

For final architectural or commercial lighting design, manufacturer IES files and professional photometric software should be used to verify the design.