Bathroom Lighting (C) Daniel Friedman Guide to Recommended Lighting Levels for Indoor Areas
Tables & Rules of Thumb for Interior Lighting

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This article series details guidelines for selecting and installing interior lighting to meet the requirements for different building areas.

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.or

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Guide to Recommended Lighting Levels Indoors

Bath light, poorly placed © D Friedman at

Many factors affect the illumination needed for a specific task. This article discusses lighting recommendations for various indoor areas and includes some RULES of THUMB INTERIOR LIGHTING.

An often overlooked factor is the age of the occupants.

At 60 years old, we need two to three times the light we needed at age 20, and also more shielding and diffusers since older eyes are more sensitive to glare.

[Click to enlarge any image]

The other main factors in determining lighting requirements are how detailed the work is and the level of contrast and reflectance of the work surface.

Table 5-21 shows the recommended lighting along with common strategies for each type of room. For task lighting, the low numbers in each range represent the light needed for simple tasks with high contrast (reading large black type on white paper).

The high number is for tasks with more detail or lower contrast (reading the newspaper). For very detailed, low-contrast work or for older persons, light levels of 100 footcandles are often needed.

Table 5-21: Suggested Lighting Strategies and Lighting Levels by Room Type (C) J Wiley, S Bliss

Interior Lighting Rules of Thumb

Task lighting © D Friedman at

The illumination level on a surface depends on many factors, including the colors of the room and furnishings and the type of lamp and fixture. High ceilings, dark colors, and diffusers on fixtures all reduce light levels. The commonly used black baffles in recessed lights reduce output by up to 40%.

Tightly focused spots produce much higher light levels than wide floods.

Rules about Distance from Light Source

The distance from the light source is also critical. Doubling the distance to a lamp reduces the lighting level by a factor of four. So moving the light closer to the task is often the simplest way to provide a big boost in lighting levels.

Rule of Thumb for Brightly-Lit Space Needs

As a starting point for design in kitchens, baths, home offices, and other brightly lit spaces, provide at least 2 watts of incandescent light or 3/4-watt of fluorescent light per square foot of floor area. In larger spaces, using multiple fixtures will provide more even lighting and reduce glare.

Downlighting Suggestions

Also, since lighting needs change throughout the day with changes in daylight and usage, it is good to provide flexibility by separately switching groups of lights and adding dimmers. Increase these minimums by 50 to 100% for:

-- Adapted with permission from Best Practices Guide to Residential Construction.

Also compare table lighting, task lighting and downlighting


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