Knowledge: Stereo Microscope Fluorescence Adapter LED Safety

The fluorescence excitation light heads for the Stereo Microscope Fluorescence Adapter use bright light-emitting diodes (LEDs). They are focused to produce strong illumination of your subjects, but they are NOT lasers and there is no danger of instantaneous eye damage from looking directly into the light. There are some reasonable LED safety precautions that should be taken in their use. We will outline those first here, then provide more detail below.

General safety precautions

  • Do not stare directly into any of the light sources.
  • Do not point any of the light sources into anyone else’s eyes.
  • Use the filter shield supplied with each light and filter set.
  • If you or anyone nearby are bothered by bright reflections you can use an opaque object, such as a sheet of cardboard, to make a shield.
  • Always use the barrier filter that comes with the light head when you are looking through the microscope and the excitation light is illuminated.
  • We have had rare anecdotal reports of individuals who are especially sensitive to blue light, reporting headaches or other effects after periods of exposure. This appears to be individual and not general. If you are affected by any of the light sources you should take extra precautions to avoid exposure. This could include use of barrier filter glasses. We can supply these in any of the wavelengths used in the SFA system.

Wavelengths

We currently offer five excitation source options with the SFA:

  • UV – Ultraviolet – ~360 – 380nm
  • VI – Violet – ~400 – 415nm
  • RB – Royal Blue, ~440 – 460nm
  • CY – Cyan, ~490 – 515nm
  • GR – Green, ~510 – 540nm

There are no known dangers of exposure to the eye or skin for the CY and GR sources.

The RB source is not known to have erythemal (skin) effects but may have photochemical effects on the retina for long exposure times. We will discuss this further below.

The VI and UV sources could potentially have both eye and erythemal effects with extended direct exposure. This can be avoided by following the General Safety Precautions outlined above.


Aversion response

We are usually protected from extended exposure to bright light sources by our natural aversion response. If exposed to a bright source we tend to look away quickly. The perceived brightness of a source is related to its wavelength, as described by its luminous efficacy. Our eyes are not equally sensitive to all wavelengths (colors) of light, so that two light sources of equal energy but different wavelength will produce different sensations of brightness. The maximum brightness response is in the green, at 555nm.

Royal Blue – The luminous efficacy at the wavelength range of the Royal Blue source is only about 10% of the maximum. The RB sources are still bright enough to produce an aversion response, but they are even more intense than they appear.

Violet and Ultraviolet – The luminous efficacy for the Violet source is very low and for the Ultraviolet it is zero, which is why ultraviolet light is also called ‘black light’ – it is there, but you can’t see it. The important point is that these light sources do not produce an aversion response so it is necessary to know that you should not stare into them. These light heads have caution labels to this effect.


Blue Light Hazard

The topic of ‘blue light hazard‘ is being considered a lot these days because of the white LED lights that are increasingly replacing conventional filament light bulbs. At the heart of white LED lights are really Royal Blue LEDs with a phosphor that absorbs much of the blue and emits a broad range of wavelengths to produce the sensation of white light. Some of the blue peak remains, however. Much of the concern about blue light is based on experiments in which rhesus monkeys were exposed to intense blue light (~440nm) for 1000 seconds (> 16 minutes), following which retinal damage was observed.

We are exposed to blue light all the time: from sunlight, from overhead fluorescent lights, in fact from any white light source. The danger, if any, would seem to come from extended eye exposure to bright sources of blue light. The best precaution is to minimize that exposure by following the general safety precautions outlined above.