Recommended Exposure Durations

The Maximum Permissible Exposure varies depending on the laser's operating mode (continuous wave or pulsed) and wavelength, according to the exposure duration, and whether the exposure is to eyes, skin, or materials. This page discusses how exposure durations can affect the MPE, especially for visible light and the Eye MPE.

Exposure durations for various situations and wavelengths


Below are some recommended exposure durations. In other words, if you have a specific situation such as “the viewer does not want laser light and thus will blink, turn away or otherwise avert from visible light”, then choose the appropriate exposure duration to use when finding the MPE. In the example, it would be 0.25 seconds, the duration for “Normal eye aversion response to bright visible light.” And using the table above, the MPE for an undesired exposure to visible light would be 2.5 mW/cm².

  • 0.25 seconds: Normal eye aversion response to bright visible light
  • 10 seconds: Normal maximum exposure time for infrared wavelengths due to natural body movements
  • 100 seconds: Maximum recommended exposure time for intrabeam exposure to ultraviolet wavelengths
  • 600 seconds: Visible wavelengths used for alignment purposes (having to look at the laser for alignment or similar tasks, for up to 10 minutes)
  • 30,000 seconds: Occupational 8-hour work day. Recommended maximum for diffuse (not intrabeam) exposure to ultraviolet wavelengths
  • 24 hours: Accumulated "on" time for ultraviolet wavelengths

Eye MPEs for visible light, selected exposure durations


Here are the Eye MPEs for visible light (400-700 nm) for selected exposure durations between 18 microseconds (18 μsec or 0.000018 sec) and 10 seconds.

  • 10 seconds: 1.01 mW/cm²
  • 1 second: 1.80 mW/cm²
  • 0.25 second: 2.54 mW/cm². This value is used for accidental, unwanted exposure to visible light, where a person is expected to blink and/or turn away within 1/4 second of experiencing a bright light.
  • 0.1 second: 3.20 mW/cm²
  • 0.01 second: 5.69 mW/cm²
  • 0.001 second: 10.1 mW/cm²
  • 0.0001 second: 18.0 mW/cm²
  • 0.000018 microseconds: 27.6 mW/cm²

For exposure durations over 10 seconds, the Eye MPE is wavelength dependent. For example, the Eye MPE for a 10 minute exposure to red 633 nm laser light is 0.253 mW/cm2; for blue-green 514 nm laser light it is 0.0167 mW/cm2.

Calculating exact Eye MPE values for visible light, 18 μsec to 10 seconds


For eye exposures between 18 microseconds and 10 seconds, you can use the following formula to determine the continuous wave visible light Eye MPE, where t is the time of exposure in seconds:



The answer will be in milliwatts per square centimeter (mW/cm²).

To calculate t to the 0.75 power, use a scientific calculator with an "xʸ" button. Enter the time in seconds, press the xʸ button, then 0.75, then the equals button.

Below is an example showing a calculator app with an xʸ button, and how to calculate the MPE for a 3 second duration. The answer rounded to two decimal places is 1.37 mW/cm².