Illuminating Progress in Microscope Lighting

For pathologists, the color rendering of a microscope’s light source is critical for seeing stained samples correctly and making a reliable diagnosis. And that’s why many pathologists continue to use halogen lamps with filters – a method over 60 years old. The halogen bulb’s color rendering enables them to view colors in the vitally important pink, cyan, and purple ranges. But is there a better solution? Today’s modern light-emitting diode (LED) light sources can render colors with equal accuracy – and offer a few added benefits. In my view, there are six good reasons for making the switch…

Color rendering measures the ability of a light source to show a sample’s “true” colors – in other words, those that would be detected by the naked eye. This can be quantitatively measured on the color rendering index (CRI), a scale that runs from 0 to 100.

Halogen light sources with filters are known for their color rendering performance, with a CRI of 100. Although early LEDs couldn’t compete, modern LEDs score equal to or better than 96 – coming close to the performance of halogen lamps and enabling researchers to see true colors (see Figure 1).

Figure 1. A comparison between a halogen lamp with filter and a modern LED light source.

In this area, LEDs tend to get a bad rap – why? The light intensity of generic white LEDs can vary drastically at different wavelengths, peaking at 400–430 nm and weak from 600–700 nm. This variability can lead to a lack of intensity in the red end of the spectrum, causing a blue shift in the colors produced. A halogen lamp with a filter, on the other hand, provides smooth, continuous characteristics across the visible light spectrum, allowing uniform illumination of every color in a sample.

Unlike their earlier counterparts, modern LEDs designed for microscopy can closely match the spectral characteristics of halogen for accurate color representation (see Figure 2).

Figure 2. Spectral distributions of a halogen lamp with a filter (left, pink), a high-end LED (center, yellow), and a generic white LED (right, blue).

In the past, pathologists relied on halogen light sources with daylight filters to provide the right color temperature for viewing stained samples; white LEDs were known for their cooler color temperature, which altered the colors of common stains (see Figure 3).

Figure 3. Differences between a halogen lamp with filter (left) and LED illumination (middle). Adding a CC filter to the LED light source mitigates the issue (right), but does not fully correct it.

Today, the answer is not so black and white. Not only can modern LEDs match the color temperature of halogen lamps with filters, but they can overcome one of the difficulties of halogens: inconsistent color temperature at different brightness levels. Whereas halogen lamps’ color temperature changes with different voltages, LEDs provide a consistent color temperature at any brightness level. Notably, eye fatigue is reduced when eyes don’t have to adapt to changes in color.

When groups observe samples together, the images need to be clear and bright. Both halogen light sources and generic white LEDs lack the brightness required for large groups to view a sample simultaneously on a multi-headed microscope. Illuminators that use filters or fly-eye lenses face the risk of even lower luminosity. Fortunately, many modern LEDs are bright enough to allow multiple viewers to observe and discuss samples with no loss of image quality.

LEDs are known for their longevity. In general, modern LED light sources can last up to 50,000 hours – approximately 25 times the lifespan of a halogen bulb. A microscope used 40 hours a week with a 50,000-hour light source should last over 24 years. With a long-lasting LED light source, you may never need a replacement – saving money, helping the environment, and reducing time spent on microscope maintenance.

Halogen and generic LEDs sometimes require the user to adjust the brightness when changing magnification. If that happens often, it can reduce observation efficiency and cause eye strain. The good news is that modern LEDs remove this step entirely with automated light intensity – speeding up observations and improving pathologists’ comfort and eye health. LEDs also produce less heat than halogen bulbs – a benefit for pathologists who may spend hours or entire days at the microscope, working in small and easily overheated rooms.

In pathology’s “halogen versus LED” debate, halogen used to emerge victorious – but today, I believe LEDs have a clear edge. With reliable color reproduction, bright illumination, power efficiency, and user comfort, LED illumination’s popularity among pathologists is sure to continue growing.

Newsletters

Receive the latest pathology news, personalities, education, and career development – weekly to your inbox.

I have read and understand the Privacy Notice*

Subscribe