Making Sense of Measurements

A meter gives you a number. The useful questions are: what does it mean, where is it coming from, and what can you do about it?

About these ranges

The ranges below are based primarily on the SBM-2024 Building Biology Evaluation Guidelines for Sleeping Areas.

These are precautionary Building Biology guidelines, not government exposure limits. They are designed especially for sleeping environments, where exposures may continue for many hours.

A measurement is more than a number. Location, duration, variability and the source itself provide useful context.

No Anomaly

Slight

Severe

Extreme

⚡

EMF Measurements

Select a measurement to learn what it is, where it comes from and how to interpret it.

⚡

AC Electric Fields

Energized wiring, cords and electrical equipment

What is it?

Electric fields occur around energized wiring and electrical equipment whenever voltage is present. Equipment does not necessarily need to be actively operating for an electric field to exist.

VOLTAGE → ELECTRIC FIELD

Common sources

Wiring inside walls Extension cords Power strips Lamps Chargers Ungrounded electronics Adjustable beds Electric blankets

Ground-referenced measurement

V/m	SBM Classification
<1	🟢 No Anomaly
1–5	🟡 Slight
5–50	🟠 Severe
>50	🔴 Extreme

Potential-free measurement

<0.3 V/m	🟢 No Anomaly
0.3–1.5 V/m	🟡 Slight
1.5–10 V/m	🟠 Severe
>10 V/m	🔴 Extreme

Body voltage

<10 mV	🟢 No Anomaly
10–100 mV	🟡 Slight
100–1000 mV	🟠 Severe
>1000 mV	🔴 Extreme

🔎 Find the source Move away from walls, cords and electrical equipment. Unplug equipment or switch off one circuit at a time and measure again.

Ground-referenced, potential-free and body-voltage measurements are different methods and should not be treated as interchangeable.

🧲

AC Magnetic Fields

Current flowing through wiring and equipment

What is it?

Magnetic fields are produced when electrical current flows through wiring and electrical equipment.

CURRENT → MAGNETIC FIELD

Common sources

Electrical panels Transformers Motors Refrigerators Appliances Induction cooktops Building wiring Utility lines

1 mG = 100 nT

mG	nT	SBM Classification
<0.2	<20	🟢 No Anomaly
0.2–1	20–100	🟡 Slight
1–5	100–500	🟠 Severe
>5	>500	🔴 Extreme

🔎 Find the source Walk slowly through the room. A sharp localized increase may indicate nearby equipment. A field that stays elevated across a larger area may point toward building wiring, net current, utility infrastructure or an external source.

📡

Radiofrequency (RF)

Wi-Fi, cellular, Bluetooth and other wireless transmitters

What is it?

Radiofrequency electromagnetic radiation is used to transmit information wirelessly. Many devices transmit intermittently or in bursts, so measurements can change rapidly.

Common sources

Wi-Fi routers Cell phones Cell towers Bluetooth Smart TVs Wireless speakers Smart-home devices Baby monitors DECT phones Neighboring wireless devices

SBM-2024 ranges

SBM specifies these ranges for peak measurements of individual RF sources.

µW/m²	mW/m²	µW/cm²	Classification
<0.1	<0.0001	<0.00001	🟢 No Anomaly
0.1–10	0.0001–0.01	0.00001–0.001	🟡 Slight
10–1000	0.01–1	0.001–0.1	🟠 Severe
>1000	>1	>0.1	🔴 Extreme

🔎 Find the source Turn transmitters off one at a time and measure again. Try Wi-Fi, phones, Bluetooth and smart equipment. If RF remains elevated, investigate windows and exterior walls for outside sources.

Why does an RF meter jump around? Wireless devices frequently communicate in short bursts. Looking at peaks and identifying the transmitter can provide information that one instantaneous reading cannot.

〰️

Dirty Electricity & VLF

Higher-frequency components associated with electrical wiring

What is it?

Household electricity in the United States is nominally 60 Hz. Electronic equipment can introduce harmonics, transients and higher-frequency components onto electrical wiring.

SBM-2024 separately evaluates higher-frequency electric and magnetic fields in approximately the 2 kHz to 1 MHz range.

Common contributors

Switching power supplies LED lighting Fluorescent lighting Dimmer switches Solar inverters Variable-speed motors Chargers Electronics

Different meters measure different things. Plug-in dirty-electricity meters may measure voltage components on wiring, while other instruments directly measure higher-frequency electric or magnetic fields. Their readings are not automatically interchangeable.

🔎 Find the source Establish a baseline, then change one thing at a time. Turn off lighting, unplug equipment, disable a dimmer or de-energize a circuit and measure again.

🔬

Additional Measurements

Other electromagnetic and indoor environmental factors

🧭

Static Magnetic Fields

Distortions of the Earth's natural magnetic field

The Earth's magnetic field is naturally present. Building Biology evaluates spatial distortions and fluctuations rather than simply the existence of the natural field.

Potential sources

Steel bed frames Innerspring mattresses Metal furniture Structural steel Magnetized materials

Spatial deviation

<1 µT	🟢 No Anomaly
1–5 µT	🟡 Slight
5–20 µT	🟠 Severe
>20 µT	🔴 Extreme

SBM also considers temporal fluctuations and compass deviation where relevant.

⚡

Static Electric Fields

Electrostatic charge on materials and surfaces

Static electricity differs from the AC electric fields produced by household wiring. Charge can accumulate on materials and surfaces.

Potential sources

Synthetic carpet Synthetic bedding Laminate flooring Plastic furniture Synthetic clothing

Surface potential

<100 V	🟢 No Anomaly
100–500 V	🟡 Slight
500–2000 V	🟠 Severe
>2000 V	🔴 Extreme

SBM specifies these surface-potential ranges at approximately 40–60% relative humidity and also considers charge dissipation time.

☢️

Radon

Naturally occurring radioactive gas that can accumulate indoors

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It can enter buildings through foundations, cracks and penetrations.

Where to investigate

Basements Crawl spaces Ground-level rooms Foundation cracks Slab penetrations

Measurements

Bq/m³ pCi/L

Bq/m³	pCi/L	SBM
<30	<0.8	🟢 No Anomaly
30–60	0.8–1.6	🟡 Slight
60–200	1.6–5.4	🟠 Severe
>200	>5.4	🔴 Extreme

Radon is ionizing radiation and is different from the non-ionizing electromagnetic fields discussed above.

💡

Light & Flicker

Brightness, spectrum, color temperature and temporal modulation

Light quality involves more than brightness. The amount of light, its wavelengths, timing, color temperature and flicker describe different parts of the light environment.

💡 Simple principle Seek abundant natural light during the day. As evening approaches, reduce both brightness and short-wavelength light. Keep the sleeping environment dark.

☀️

Illuminance & Lux How much visible light reaches a surface

+

Illuminance describes the amount of visible light reaching a surface. Lux (lx) is the unit used to measure it.

☀️ Day

100–100,000 lux

The broad Building Biology range reflects the enormous difference between indoor and outdoor daylight.

🌅 Evening

10–100 lux

Progressively dim the environment as bedtime approaches.

🌙 Night

<1 lux

Keep the sleeping environment as dark as practical.

Recommendation Get outside during the day when practical. Indoors, maximize useful daylight. At night, use fewer and dimmer light sources rather than brightly illuminating the room.

👁️

Melanopic Light The circadian light signal reaching your eyes

+

Ordinary lux measures visual brightness. It does not completely describe how strongly light stimulates melanopsin-containing retinal cells involved in circadian timing.

Melanopic EDI is a more useful measurement for this purpose.

☀️ Day

≥250

melanopic lux at the eye

🌅 Before bed

≤10

melanopic lux during the ~3 hours before bed

🌙 Sleep

≤1

melanopic lux at the eye

Recommendation Think bright days and dark nights. During the evening, reduce both total brightness and melanopic output.

🌈

Spectrum & Wavelengths Which wavelengths make up the light

+

White light contains multiple wavelengths. Two bulbs that look equally white can have very different spectral distributions.

Some artificial lights contain pronounced peaks and gaps, while sunlight has a much broader spectral distribution.

☀️ During the day Favor natural daylight and broad-spectrum artificial lighting when needed. Avoid choosing a light solely because it appears bright or white.

🌅 During the evening Reduce strong short-wavelength output, particularly blue/cyan wavelengths that produce a strong melanopic signal. Favor dimmer, warmer light.

🌈 Read more about wavelengths & sunlight →

🎨

Color Temperature How warm or cool the light appears

+

Correlated color temperature, measured in Kelvin (K), describes whether white light appears warm or cool.

☀️ Day

4000–6000 K

Building Biology range for daytime artificial lighting.

🌅 Evening

1500–3000 K

Warmer light as bedtime approaches.

🌙 Sleep

Dark

If light is necessary, use very dim amber/red light.

Kelvin isn't the whole story. Two 2700 K bulbs can have different spectra. Spectrum and melanopic output tell you more about the biological light signal than color temperature alone.

〰️

Flicker Rapid changes in light output over time

+

LEDs and other artificial lights can rapidly vary in brightness because of their electronics and power supply. Flicker can be present even when you do not consciously see the light flashing.

Common sources

LED bulbs LED drivers Fluorescent lights Dimmer switches Screens Power supplies

Recommendation Favor lighting with very low temporal modulation. Building Biology favors approximately ≤1–2% flicker in the relevant frequency range.

When shopping for lighting, actual flicker measurements are more informative than a package simply saying “flicker-free.”

🎭

Color Rendering (CRI) How naturally colors appear under the light

+

The Color Rendering Index describes how accurately colors appear under a light source compared with a reference source.

Recommendation: CRI >95 Favor high-quality, high-CRI lighting when choosing artificial light.

CRI is only one characteristic. A high-CRI bulb can still have undesirable flicker or an inappropriate spectrum for the time of day.

💡 The easy version

Morning + day: get outside and seek abundant natural light. Indoors, favor broad-spectrum, high-CRI, low-flicker lighting.

Evening: make the environment dimmer and warmer, roughly 1500–3000 K, while reducing short-wavelength and melanopic light.

Sleep: darkness. If light is necessary, keep it extremely dim.

🔊

Sound

Audible noise, low-frequency sound and vibration

Common sources

Traffic Aircraft HVAC Refrigerators Pumps Transformers Ventilation Neighboring buildings

What can be measured?

dB dB(A) dB(C) Frequency Low-frequency noise Vibration

Pattern

• Continuous
• Intermittent
• Peaks

Frequency

• Tonal sounds
• Hum
• Low-frequency components

Timing

• Daytime
• Nighttime
• Equipment cycles

A single decibel value does not describe the entire acoustic environment. Frequency, peaks, duration and timing can provide additional information.

🌿

Indoor Air & Mold

Moisture, particles, biological contaminants, gases and chemicals

Indoor air is not one measurement. Different clues call for different investigations.

🌬️ Ventilation & combustion

CO₂ Carbon monoxide Humidity Temperature Air exchange

🌫️ Particles & fibers

Fine particles Dust Fibers Soot

🍄 Mold, yeast & bacteria

Look for

• Visible mold
• Musty odors
• Past flooding
• Plumbing leaks
• Roof leaks
• Condensation

Measure

• Material moisture
• Relative humidity
• Surface temperature
• Biological material when appropriate

Look behind

• Walls
• Flooring
• Cabinets
• Attics
• Crawl spaces
• HVAC components

🌾 Allergens

Dust mites Pets Pollen Other biological allergens

🧪 VOCs & chemical pollutants

VOCs Formaldehyde Solvents Fragrances Pesticides

Common clues

New furniture New flooring Renovations Cleaning products Gas appliances Attached garage Pesticides Water damage Poor ventilation

Follow the clue. A musty odor, new flooring, combustion source and water leak call for different investigations rather than the same generic air-quality test.

🔎

Using Your Measurements

Turn readings into useful information

🔎

How to Find the Source

A simple five-step investigation

1. Measure where you spend time.

Start at the bed, desk, couch or another location where you actually spend hours.

2. Move around slowly.

Look for patterns. Does the reading increase near a wall, cord, outlet, appliance, window or piece of furniture?

3. Change one variable.

Unplug one device, move one cord, switch off one transmitter or de-energize one circuit.

4. Measure again.

If the reading changes substantially, you've learned something about the source.

5. Verify.

Repeat the experiment before making major changes. Reproducible measurements are more useful than chasing a single meter reading.

About these guidelines: The classifications shown on this page are based primarily on the Standard of Building Biology Testing Methods SBM-2024 Evaluation Guidelines for Sleeping Areas. They are precautionary Building Biology assessment ranges, not regulatory exposure limits or medical diagnostic thresholds.

Measurements depend on the instrument, frequency range, measurement method, location, duration and behavior of the source. This guide is educational and is not a medical diagnostic tool.

RF Measurements and Observed Effects