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Screen

Belongs to:
Home
Synonyms:
Cathode-ray tube screen, Flat panel display, Flat screen, Monitor, PC screen, Plasma display panel, TV screen, Tube screen, Visual display terminal, Visual display unit
Description:

Measured values for both TV and PC screens can be found under "screen". As far as possible, they are distinguished acc. to the technology employed (e.g. cathode ray tubes, LCD screens). Flat screens are based on LCD or plasma technology; the employment of cathode ray tubes is not feasible due to space requirements.

For a tube screen, the central element is a cathode ray tube. During its thermic heating, electrons are emitted and deflected by a magnetic field of a certain frequency. In horizontal direction, the deflection frequency is 15.625 kHz, in vertical direction 50 Hz. Having hit the fluorescent screen, the electrons generate a light spot. Its brightness dependent on its position on the screen provides information about the image content. In order to depict a complete picture, all pixels are passed line-by-line.

In contrast to that, the main components of an LCD (Liquid Chrystals Display) screen are liquid crystals. Each pixel corresponds with a crystal. Its transparency can be controlled by a given voltage without influencing the adjacent crystals: Once a voltage has been employed, the crystals change their permeability for polarized light. The polarized light originates from a background illumination, followed by a polarization filter.

Frequency ranges:
  • 50–60 Hz (for non-tube screens)
  • 50 Hz–15.625 kHz (for tube screens)
Type of field:
electric and magnetic

Measurements (acc. to literature)

TV screen
Measurand Value Feature Remarks
electric field strength 60 V/m (maximum) tube screen at a distance of 30 cm [1]
electric field strength 12.727 kV/m (maximum) tube screen at the surface of the device [2]
magnetic flux density 0.0075 µT (maximum) not specified at a distance greater than 2 m [3]
magnetic flux density 0.017793 µT (maximum) not specified spatially averaged value from 3 - 30 cm [4]
magnetic flux density 0.0201 µT (maximum) tube screen maximum value at a distance of 10 cm at a frequency range from 150 kHz - 30 MHz [5]
magnetic flux density 0.0331 µT (maximum) tube screen maximum value at a distance of 50 cm at a frequency range from 150 kHz - 30 MHz [5]
magnetic flux density 0.036 µT (maximum) not specified at a distance of 1 -2 m [3]
magnetic flux density 0.07 µT (mean, measured) not specified average value of 73 devices at a distance of 100 cm; measurement bandwidth: 40 - 800 Hz [6]
magnetic flux density 0.1–1.71 µT (measured) not specified of 5536 sample points; measurement bandwidth: 40 - 800 Hz [7]
magnetic flux density 0.135 µT (maximum) not specified at a distance of less than 1 m [3]
magnetic flux density 0.19 µT (mean, measured) not specified average of 27 devices at a distance of 50 cm; measurement bandwidth: 0 - 3000 Hz [8]
magnetic flux density 0.2 µT (maximum) not specified at a distance of 60 cm [9]
magnetic flux density 0.2 µT (maximum) not specified at a distance of 15 cm [10]
magnetic flux density 0.26 µT (mean, measured) not specified average value of 73 devices at a distance of 50 cm; measurement bandwidth: 40 - 800 Hz [6]
magnetic flux density 0.33 µT (maximum) not specified at a distance of 56 cm [11]
magnetic flux density 0.38 µT (measured) not specified of 5536 sample points; measurement bandwidth: 40 - 800 Hz [7]
magnetic flux density 2 µT (maximum) not specified at a distance of 30.48 cm [9]
magnetic flux density 2.19 µT (mean, measured) not specified average of 27 devices at a distance of 10 cm; measurement bandwidth: 0 - 3000 Hz [8]
magnetic flux density 2.69 µT (mean, measured) not specified average value of 73 devices at a distance of 5 cm; measurement bandwidth: 40 - 800 Hz [6]
magnetic flux density 431 µT (maximum) tube screen at the surface of the device at 50 Hz [12]
laptop screen
Measurand Value Feature Remarks
electric field strength 20 V/m (measured) not specified at a distance of 0.3 m; measurement bandwidth: 30 - 40 kHz [13]
PC screen
Measurand Value Feature Remarks
electric field strength 0.93 V/m (maximum, measured) flatscreen, not specified Smart board from unspezified manufacturer, measurement at the surface, frequency: 5 - 15 kHz, measurement bandwidth: 300 Hz - 10 MHz [14]
electric field strength 15–25 V/m (min-max value) LCD screen at a distance of 30 cm [13]
electric field strength 155.7 V/m (maximum, measured) flatscreen, not specified Touchscreen from Packard Bell, disctance: 5 cm from back, frequency: 44 kHz, measurement bandwidth: 300 Hz - 10 MHz [14]
electric field strength 10–20 kV/m (measured) not specified at a distance of 0.3 m [13]
magnetic field strength 0.3 A/m (maximum, measured) flatscreen, not specified Touchscreen from Packard Bell, disctance: 5 cm from back, frequency: 44 kHz, measurement bandwidth: 300 Hz - 10 MHz [14]
magnetic flux density 6.5 nT (mean) tube screen at a distance of 50 cm to the antenna; measurement bandwidth: 10 kHz - 150 k Hz [5]
magnetic flux density 0.02–0.81 µT (measured) LCD screen of 1601 sample points; measurement bandwidth: 40 - 800 Hz [7]
magnetic flux density 30.5 nT (mean) tube screen at a distance of 10 cm; measurement bandwidth: 150 kHz - 30 MHz [5]
magnetic flux density 33.1 nT (mean) tube screen at a distance of 20 cm to the antenna; measurement bandwidth: 150 kHz - 30 MHz [5]
magnetic flux density 39.8 nT (mean) tube screen at a distance of 10 cm to the antenna; measurement bandwidth: 10 kHz - 150 kHz [5]
magnetic flux density 0.05 µT (mean, measured) LCD screen average of 12 devices at a distance of 50 cm; measurement bandwidth: 0 - 3000 Hz [8]
magnetic flux density 0.11 µT (mean, measured) LCD screen of 1601 sample points; measurement bandwidth: 40 - 800 Hz [7]
magnetic flux density 0.13 µT (mean, measured) LCD screen average 12 devices at a distance of 10 cm; measurement bandwidth: 0 - 3000 Hz [8]
magnetic flux density 1.2 µT (maximum, measured) LCD screen at a distance of 80 cm [15]
magnetic flux density 4 µT (maximum) LCD screen at a distance of 40 cm [15]
magnetic flux density 25 µT (maximum) LCD screen directly in front of the device [15]
touchscreen
Measurand Value Feature Remarks
electric field strength 12.5 V/m (mean, measured) - at a distance of 15 cm; examined frequency: 44 kHz; location: school [14]
electric field strength 33.34 V/m (measured) - in front of the touchscreen on the right side at a distance of 21.5 cm; examined frequency: 44 kHz; location: school [14]
electric field strength 59.84 V/m (measured) - at the right side of the touchscreen at a distance of 21.5 cm; examined frequency: 44 kHz; location: school [14]
electric field strength 155.66 V/m (measured) - at the right side of the touchscreen at a distance of 21.5 cm; examined frequency: 44 kHz; location: school [14]
electric field strength 160 V/m (mean, measured) - at a distance of 5 cm; examined frequency: 44 kHz; location: school [14]
magnetic field strength 0.11 A/m (measured) - in front of the touchscreen on the right side at a distance of 21.5 cm; examined frequency: 44 kHz; location: school [14]
magnetic field strength 0.19 A/m (measured) - at the right side of the touchscreen; examined frequency: 44 kHz; location: school [14]
magnetic field strength 0.33 A/m (measured) - at the right side of the touchscreen at a distance of 21.5 cm; examined frequency: 44 kHz; location: school [14]
magnetic field strength 0.4 A/m (mean, measured) - at a distance of 5 cm; examined frequency: 44 kHz; location: school [14]

References

  1. (2018): [Radiation and radiation protection]
  2. Leitgeb N et al. (2008): Electric emissions from electrical appliances.
  3. Behrens T et al. (2004): Quantification of lifetime accumulated ELF-EMF exposure from household appliances in the context of a retrospective epidemiological case-control study.
  4. Mader DL et al. (1992): Residential exposure to 60-Hz magnetic fields from appliances.
  5. Kurokawa Y et al. (2004): Evaluation of residential exposure to intermediate frequency magnetic fields.
  6. Preece AW et al. (1997): Magnetic fields from domestic appliances in the UK.
  7. Kim YS et al. (1997): Exposure of Workers to Extremely Low Frequency Magnetic Fields and Electric Appliances
  8. Ainsbury EA et al. (2005): An investigation into the vector ellipticity of extremely low frequency magnetic fields from appliances in UK homes.
  9. Lacy-Hulbert A et al. (1998): Biological responses to electromagnetic fields.
  10. Preece AW et al. (1999): Assessment of Human Exposure to Magnetic Fields Produced by Domestic Appliances
  11. National Research Council (1997): Possible health effects of exposure to residential electric and magnetic fields.
  12. Leitgeb N et al. (2008): Magnetic emission ranking of electrical appliances. A comprehensive market survey.
  13. Moser M et al. (2006): [Non-ionizing radiation and health protection in Switzerland: basic information].
  14. Van Den Bossche M et al. (2015): In situ exposure assessment of intermediate frequency fields of diverse devices.
  15. Farag AS et al. (1998): Electromagnetic fields in the home.