Visible Light Transmission, commonly abbreviated as VLT, describes the percentage of visible light that passes through a lens or filter.

For laser safety eyewear, VLT can help indicate how much visible light users can expect to transmit through the filter. A higher VLT generally allows more visible light through, while a lower VLT indicates a darker filter.

However, VLT should not be confused with optical density. OD describes attenuation of specified laser wavelengths, while VLT relates to the transmission of visible light.

This distinction is important when choosing laser safety glasses. A dark-looking lens does not automatically provide a high OD rating against a particular laser wavelength. Conversely, a filter with a relatively high VLT can still provide substantial attenuation at its specified laser wavelengths.

The correct eyewear should therefore be selected using the documented wavelength and OD specifications first. VLT can then help determine whether the eyewear provides suitable visibility for the intended task.

For applications such as laser alignment, medical procedures, laboratory work and industrial operation, maintaining useful visibility can make the eyewear more practical to wear consistently.

Understanding VLT helps users interpret laser safety eyewear specifications more accurately and avoid selecting protection based purely on lens darkness or appearance.