Difference Between Excitation and Emission Filter

The key difference between excitation and emission filter is that excitation filter is important in lightening up the object under the examination of microscope whereas emission filter is important in keeping the surrounding of the object as dark as possible.

The terms excitation and emission filters are mainly used regarding the fluorescence microscopy that operates based on optical filters. There are three components in a typical fluorescence microscopic instrument: excitation filter, dichroic beamsplitter, and emission filter.

1. Overview and Key Difference
2. What is an Excitation Filter
3. What is an Emission Filter
4. Excitation vs Emission Filter in Tabular Form
5. Summary – Excitation vs Emission Filter

What is an Excitation Filter?

An excitation filter is a type of optical glass filter that is useful in the selection of the excitation wavelength of light. Usually, it is a high-quality optical glass widely used in fluorescence microscopy and spectroscopic applications where we need to select a wavelength from a light beam that comes from a light source.

Mostly, excitation filters tend to select light having a short wavelength that comes from an excitation light source. This is because this type of light can carry energy that is sufficient only for the fluoresce of an object that is examined under the microscope.

Figure 01: Examination under a Microscope in the Presence of Fluorescence

There are two major types of excitation filter glasses as short pass filter glasses and bandpass filter glasses. These two types of filter glasses are different from each other according to the form of notch filters or deep blocking filters that are used as emission filter glasses. However, there can be some other types of excitation filter glasses as well, such as monochromators, wedge prisms that are coupled with a narrow slit, and holographic diffraction gratings.

Commonly, an excitation filter glass comes in a package with an emission filter and a dichroic beam splitter in a cube. Therefore, we can insert these two glasses together as a combination into the microscope. The dichroic beam tends to control the wavelength of the light that enters each filter glass.

What is an Emission Filter?

An emission filter is a type of optical glass that allows the wavelengths emitted by the fluorophore to pass through it. This optical glass is named an emitter or barrier filter as well. It is named a barrier filter because it can block all the undesired light outside the band of excitation energy that comes from the excitation light. This barrier filter allows the background of the object that is under examination from a microscope to be the darkest as possible.

Usually, an emission filter glass comes in a package with an excitation filter and a dichroic beam splitter in a cube. Therefore, we can insert these two glasses together as a combination into the microscope. There, the dichroic beam tends to control the wavelength of the light that enters each filter glass.

What is the Difference Between Excitation and Emission Filter?

There are three components in a typical fluorescence microscopic instrument that includes an excitation filter, dichroic beamsplitter, and an emission filter. The key difference between excitation and emission filter is that excitation filter is important in lightening up the object under the examination of microscope whereas emission filter is important in keeping the surrounding of the object as dark as possible.

The below infographic summarizes the differences between excitation and emission filter in tabular form.

Summary – Excitation vs Emission Filter

The key difference between excitation and emission filter is that excitation filter is important in lightening up the object under the examination of microscope whereas emission filter is important in keeping the surrounding of the object as dark as possible.

Reference:

1. “Excitation Filter.” Wikipedia, Wikimedia Foundation, 9 Jan. 2021, Available here.
2. “Fluorophores and Optical Filters for Fluorescence Microscopy.” Edmund Optics Worldwide, Available here.