Ring lights are commonly used for stereo microscopes, and are mounted to the nosepiece or objective cover under the body so they can illuminate the sample from above.

While not everyone needs to do extensive research to find the best ring light illuminator for their application, it's a good idea to do a little investigation before buying one. Let's look at some features of ring lights and how they affect the quality of the image you get through your microscope.

Brightness / Intensity

Ring lights vary in the amount of light they put out. Though many are sufficient for most applications, two situations in which you'll want to pay attention to the brightness are:

• If you're working at high magnifications (90x and above). Higher magnifications require higher illumination intensities to maintain overall brightness in the field of view.
• If you're doing photomicrography through a separate phototube* rather than taking photos through the eyepieces, unless your microscope has a beam splitter that allows all light to be directed through either optical path (100% to the eyepieces or 100% to the phototube). If it doesn't, then the light is probably getting split 50/50 or 80/20 (e.g. 80% to the phototube and 20% to the eyepieces).

In either of these cases you might want to compare the lumens or candela specifications of different ring light options to ensure you're getting the best value.

LED vs Halogen

Halogen illuminators used to be popular due to their advantages over standard incandescent light sources. LED illuminators have upped the ante and now possess similar advantages over halogen, including:

• Much longer bulb life (no more lamps to replace)
• Higher (whiter) color temperature
• Consumes less power
• Cool (helps when looking at heat-sensitive samples like embryos)

Some believe LED illuminators don't quite have the same level of intensity as halogen, but that's no longer the case for more recent models as technology has caught up.

All That Glitters...

Picture this: You've got your nice, shiny sample sitting on the table ready for analysis, exploration, and discovery. You can't wait to dig into its minute details, dissecting its features and flaws, or simply observing its beauty. You eagerly switch on the brand new illuminator and boom, 64 bright dots shine in your face. Not what you expected?

Samples that are reflective, shiny, or mirror-like will sometimes reflect the bulbs of an LED ring light whose array of bulbs is exposed. If this is bothersome, you can obtain a diffuser or translucent cover so you don't see the reflection, and to ensure your camera doesn't capture underexposed or overexposed areas that make it difficult to evaluate the sample.

Other Considerations

• Some models feature quadrant lighting, or the ability to dim in quarter circle increments, which may be convenient for certain applications.
• Be sure the ring light you choose fits the diameter of the objective cover it will mount to. Sometimes the objective cover is tapered (as in Meiji Techno's EMT Series), in which case you'll need an adapter to accommodate ring lights.
• Check whether it will mount to any auxiliary lenses you wish to use.
• A good ring light would have variable intensity or dimmer capability so you can change the intensity of your ring light. As you go up and down the magnification range on your microscope, the level of brightness in your field of view also changes, so you'd want to adjust the dimmer knob to keep it consistent.

* Also "trinocular tube", "trino tube", "trinotube", "trino-tube", "trino", "tube", and myriad other permutations and combinations the creative mind can conjure.

‍