Monochromator or Filter-Based Plate Reader? How to Choose

Aug. 18, 2025

Monochromator or Filter-Based Plate Reader? How to Choose

Microplate readers can make quick work of sample analysis across multi-well plates by quantifying key signals like fluorescence, absorbance, luminescence, and turbidimetry. Not all plate readers carry the same features, however, and it pays to know how your lab’s needs intersect with current technologies.

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One of the most common questions researchers have when buying is whether to choose a monochromator- or filter-based plate reader.

This guide breaks down the optical mechanisms behind monochromators and filters, along with the pros and cons of each option and why you might choose one over the other.

What are monochromators and filters, and how are they used in microplate readers?

Microplate readers work by selectively emitting or detecting ranges of light. To select the relevant wavelength(s) for analysis, today’s plate readers use either monochromators or optical filters.

Monochromator plate readers

A monochromator – with a name rooted in the Greek words for “single color” – is a device that can mechanically isolate individual wavelengths from a beam of light. Microplate readers containing monochromators can be set to emit or detect light at any specific wavelength within their range for absorbance and emission measurements of samples.

Plate reader monochromators function by diffusing light through a diffraction grating, using a series of mirrors to precisely separate the instrument’s light source beam into single-color components. The monochromator then passes only the selected wavelength of light through to the sample. From there, the sample emits its own light back through the system of selective diffraction grating and mirrors so that, again, only a single wavelength reaches the detector for signal reading.

Filter-based plate readers

Filters are optical devices that only allow certain wavelengths of light to pass through them. Filter-based microplate readers have both excitation filters, which filter light going from instrument to sample, and emission filters, which filter light going from sample to detector.

The wavelength range that a filter can transmit is referred to as the filter’s bandwidth. Light outside of a filter’s bandwidth cannot pass through.

What is the difference between filter-based and monochromator-based plate readers? Which is better?

There is no one “right” option for plate readers, and the best choice will depend on your lab’s needs.

In general, microplate readers with monochromators offer the flexibility to select any wavelength and are ideal for running diverse assays or full spectral scans. Filter-based microplate readers are an affordable and robust option for customers performing routine assays.

Summary of key benefits and uses of monochromator-based vs. filter-based microplate readers

Pros of monochromator-based plate readers

Increased flexibility—Monochromators enable selection of any wavelength of light within the instrument range without the need to change physical filters. Monochromator-based microplate readers do not require hardware changes or updating to run new assays or detect fluorophores with diverse spectra. This tunable wavelength selection allows flexibility for labs performing a diverse array of assays and experiments that require different wavelengths for detection. With monochromators, labs do not need to purchase additional filters to analyze different fluorophores and assays, making monochromator-based instruments more adaptable to future laboratory needs.
Precise wavelength selection—Monochromators enable fine-tuning of the wavelength to meet the specific requirements of a dye or experiment, which is critical for developing custom assays and optimizing assay performance. This feature is particularly beneficial when working with fluorophores that have nonstandard spectral characteristics such as close excitation and emission peaks or small Stokes shifts (for instance, GFP and other fluorescent proteins, see Figure 2).
Full spectral scanning—Monochromators offer the ability to scan all wavelengths in the instrument’s range, enabling reading of the entire absorbance or fluorescence spectra. Spectral scanning is useful in characterizing and determining absorbance and emission peaks for an assay or fluorophore when the full spectra is not known, or in assays with spectral shifts.
Reduced spectral cross talk—Because they can detect all wavelengths and have a narrow measurement bandwidth, monochromator-based microplate readers allow better spectral resolution between close wavelengths, resulting in reduced cross talk and enhanced sensitivity for assays and dyes with overlapping spectra.

Cons of monochromator-based plate readers

Increased cost and maintenance—Adjustment of the position of the diffraction grating and movement of mirrors that allow for wavelength selection in monochromator-based microplate readers requires more complex mechanics, which increases cost and can make these plate readers more difficult to maintain. Monochromators also require more powerful light sources, which can add to their expense.
Less sensitive with luminescence and time-resolved fluorescence—Microplate readers that use monochromators are not as efficient in detecting light emission and are not optimal for luminescence and time-resolved fluorescence (TRF) assays.

Pros of filter-based plate readers

Lower cost—Because filter-based microplate readers have fewer moving parts, they are less expensive and require less maintenance than microplate readers with monochromators. Filters also transmit light more efficiently and do not need a strong light source, which further reduces their cost.
Excellent for routine assays—Filter-based microplate readers are a cost-effective and simple option for customers performing routine assays with standard dyes and fluorophores.
Higher sensitivity in certain applications—Filters allow a specific wavelength range or bandwidth of light to pass through and thus are more efficient at transmitting light than monochromators, which only transmit a fraction of light to and from the sample. This efficiency in light transmission for filter-based microplate readers increases sensitivity and results in lower detection limits in luminometric and TRF assays. Filter-based plate readers are necessary for assays that require larger bandwidths of light for high sensitivity, such as AlphaScreen assays.

Cons of filter-based plate readers

Less flexibility—Filters have fixed wavelength ranges, so the selected filter must match the wavelength requirements of the fluorophore or assay. This limits the flexibility of filter-based plate readers to run assays that do not match the wavelength range of the existing filters. In this case, labs may need to acquire new filters.
Lack of spectral scanning—Filter-based microplate readers cannot be used to run full spectral scans to determine absorbance and emission spectra and peaks for novel dyes or to characterize new assays.
Lower spectral resolution—Filters have a relatively wide wavelength range and allow a broad spectrum of light to pass through. This makes it difficult to distinguish between different wavelengths within the filter’s bandwidth. Due to their broader wavelength range, filters are less effective at differentiating between fluorophores with close spectral overlap or detecting fluorophores with small Stokes shifts than monochromators, which allow fine tuning of specific wavelengths by selectively isolating a narrow band of light for illumination and detection (see Figure 2).
Less adaptable—Microplate readers with filter-based detection are less adaptable to future laboratory needs since new filters may need to be purchased to run assays with different wavelength requirements.

Thermo Scientific microplate reader options

Thermo Scientific offers microplate readers with both monochromator- and filter-based wavelength selection capabilities. For plate readers suitable for absorbance assays, the Multiskan FC Microplate Photometer uses filters to select wavelengths for absorbance measurements, while the Multiskan SkyHigh Microplate Spectrophotometer is a UV/Vis microplate spectrophotometer that uses a monochromator for wavelength selection. The Varioskan ALF and Varioskan LUX Multimode Microplate Readers have both filter- and monochromator-based optics for wavelength selection depending on which detection technology is used.

» Find the best Thermo Scientific microplate reader for your lab

Depending on laboratory needs, a filter-based microplate reader may be sufficient or a microplate reader with the added flexibility of a monochromator may be the best choice. Hybrid plate readers such as the Varioskan ALF and Varioskan LUX Multimode Microplate Readers use both filters and monochromators for wavelength selection, offering another option for labs that may need filter-based detection for certain assays or applications, and monochromator-based detection for others.

Learn more about microplate readers»

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Plate and Frame Filter Press vs Recessed Plate Filter ... - Met-Chem

Filter Press Diaphragm Pumps

Air operated diaphragm pumps are used with filter presses to pump sludge from the bottom of the sludge holding tank into the filter press. These pumps are ideal because they can handle the slurry which is generally about the consistency of a milkshake.

The diaphragm pump usually starts out slowly and gradually ramps up. Once the pump starts to slow back down, (30-60 seconds between thrusts), it is usually an indicator that the filter press is full. At this point, the feed pump should be turned off and the valves on the filter press closed as the operator prepares to operate the air-blow-down process.

The diaphragm pump can be manually turned up or an Automatic Pump Control system may be added. This starts the pump at 25 psi, then moves up to 50, 75 and finally 100 psi which is standard operating pressure for the pump.

Met-Chem provides diaphragm pumps in the following sizes: 1”, 1.5”, 2” and 3”. The material of construction ranges from cast iron, aluminum, polypro or stainless steel.

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With the purchase of a new Met-Chem filter press, Met-Chem can mount your air operated diaphragm pump to the legs of your filter press. This option also includes a flex hose that connects the outlet of the diaphragm pump to the center feed pipe, an air filter, a regulator, and an oiler. We can also provide a mounted diaphragm pump for your existing press.

Automatic Filter Press Pump Control System

The Met-Chem Automatic Pump Control System is used in conjunction with an air operated diaphragm pump to automatically increase the feed pump pressure at predetermined intervals during the filter press filling cycle. If the pump runs at a higher initial pressure, the filter cake will become a packed layer of solids on the filter cloth. This will restrict the flow of the slurry thereby creating a very dense coating of the filter cake. This can cause the cloths to blind off and not allow further filtration. Starting at a lower feed pressure allows a soft layer of slurry particles to be deposited on the filter cloth. This initial layer becomes the filtering media which will enhance the filterability of the incoming slurry.

The automatic pump control system automatically and gradually increases the feed pressure in four stages during the filling cycle. These stages are adjustable to suit your slurry and solids concentration. However, it is commonly set at increments of 25 psi. (25, 50, 75, 100). By monitoring the feed pump flow sensor, during the final pressure stage, the operator will be able to determine the cycle completion.

The Automatic Pump Control System also incorporates a low hydraulic pressure safety shut down the device. If there is not enough hydraulic clamping pressure present, the system will completely shut down, eliminating any possible leaking from between the filter plates.

The pump control system allows your filter press to run at its optimum efficiency creating dryer filter cakes, reducing disposal costs, reducing operator time and increasing the life of your filter cloths and feed pumps.

This system can be incorporated with a new filter press from Met-Chem, a used unit or even your own existing press.

Spare Parts Kit

Met-Chem is pleased to offer our spare parts kit which includes our 5 piece center feed pipe assembly, a head, tail, and 2 intermediate filter press cloths, and 100 foot of gasketing material. These are essential items for the operation of the filter press. A cracked pipe, ripped cloth, or torn gasket can happen anytime and having these items in your stock will ensure you will be back up and running in no time.

Center Feed and Manifold Filter Press Upgrades

Filter Press Center Feed and Manifold Upgrades

A center feed pipe assembly on a filter press should be able to last many years the same way any other type of plumbing will. However, if the material of the center feed pipe assembly is not strong enough to handle the corrosiveness of the solution running through the press then the center feed pipe assembly can corrode.

For cases of corrosive material or high temperatures, Met-Chem is pleased to offer upgrades from our standard center feed pipe and manifold. We are able to upgrade to CPVC, Carbon Steel, 304 or 316SS Stainless Steel, and Titanium. Met-Chem can also provide additional manifold upgrades such as automatic valves

The center feed pipe is what connects the filter press to the product that needs to be filtered. The center feed pipe assembly consists of five different parts. The first part is the lock nut which fastens on the center feed pipe and connects to the outside of the press. The pipe, which is the second part, goes through the head of the filter and all the way through the head plate of the filter press. The third part of the center feed pipe assembly is a gasket which ensures the assembly is watertight. Next, is the clip nut seat which fastens the assembly to the head plate. This part of the assembly will always stay in place unless you are replacing the assembly or one of its parts. The final part, the cloth clip nut, will be removed often as it is screwed into the cloth clip nut seat after the head cloth is put on the head plate. The cloth clip nut needs to be tightened in order to keep the cloth in place. Met-Chem provides a tool to make this process easier. The Met-Chem Spanner Wrench is a specially designed tool that can be used to loosen and tighten the cloth clip nut when changing the head cloth on a filter press. This tool can be very helpful as the cloth clip, but it has a design that requires a unique tool to tighten and loosen it.

Longer Legs and Filter Press Sludge Disposal Chute

Longer Legs and Sludge Disposal Chute for Filter Presses

Met-Chem can provide longer legs and a disposal chute on your new filter press. This is especially useful if you are releasing the sludge from the press into a sludge bag or a drum. The chute will direct the sludge directly into your container. If you plan to use a sludge disposal bag, we can add hooks to the chute so that the sludge bag can be hung from the frame of the press.

For some larger presses, we can build a catwalk along with the disposal chute in order to accommodate a roll-off container.

Sludge Dumpster

Filter Press Sludge Dumpster

Sludge Dumpsters are used directly under the filter press to catch the sludge that is released from the filter press during cleaning. The dumpster is on casters for easy mobility. They are also equipped with forklift slats for convenient use with a tow motor. The operator can move the dumpster to a roll-off container with the forklift and then pull the release pin for easy emptying. The dumpster can then be snapped back to the upright position and put back under the filter press.

Backer Plate for Smaller Filter Press Batches

Filter Press Backer Plate for Smaller Batches

If you produce varying size batches of wastewater and subsequently less sludge, or if the overall volume of waste that is generated at your facility has been reduced, you can still utilize your existing filter press. With the purchase of a backer plate, you can alter the holding capacity of your press to meet your individual batch needs.

A backer plate provides support to the tail plate so that it can be moved anywhere in the plate pack in order to isolate the chambers between the feed end and the tail plate. If you try to use the tail plate in a different position in the plate pack without the backer plate, you run the risk of damaging the chamber of the tail plate.

There are different kinds of backing plates. Some are made of plastic and look much like a standard plate; we prefer to use ~3/8” thick flat stock steel and cut an outline of a plate. This is clearly visible when placed in the stack so that all around know that the filter press is not at full capacity. This steel backing plate is then painted with the same two-part epoxy coating as the frame of the filter press.

Filter Press Plate Shifters

Our standard filter presses can be operated manually. However, Met-Chem manufactures four types of filter press plate shifters to make operating your filter press easier, safer and more efficient. Manual filter presses require more time and attention than the same filter press with an automatic plate shifter.

Semi-Automatic
Pendant
Fully Automatic
Super Shifter

For some larger presses, we can build a catwalk along with the disposal chute in order to accommodate a roll-off container. Start-Up Assistance / Installation

Start-Up Assistance/Installation

The start-up and installation options are available with all Met-Chem waste treatment equipment. We can provide full support as you get your system up and running. We have installation technicians and technical representatives that we can send to your facility to make sure the system is running as it should based on the engineering and design.

Our services include but are not limited to:

Design and build the equimpent per your specs
Load, ship, and unload equipment
Install and rig equipment in facility
Electrical and plumbing connections
Train employees
Debug any issues and solve any equipment/installation troubles

All units and systems are complete with manuals and support. However, if you need someone to come to your facility, we will be happy to quote you on that as well.

Learn more about our Start-Up Assistance and Installation

If you are looking for more details, kindly visit Chamber/Recessed Filter Plate.

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Monochromator or Filter-Based Plate Reader? How to Choose