Laser Diffraction vs DLS: Key Differences
September , 2025
Particle size analysis is a foundational measurement across nanotechnology, pharmaceuticals, materials science, and environmental applications. Among the available techniques, Laser Diffraction and Dynamic Light Scattering (DLS) are two of the most widely used. Each technique interprets particle behavior through light interactions, but their capabilities, limitations, and optimal use cases differ significantly, especially in the submicron range and highly polydisperse systems.
In this article, we break down how each method works, where they perform best, and how scientific literature characterizes their strengths and limitations.
How Each Method Works
Dynamic Light Scattering (DLS)
DLS measures fluctuations in scattered light caused by the Brownian motion of particles. These fluctuations are interpreted through correlation functions to determine particle diffusion coefficients, which are then transformed into hydrodynamic diameters.
The primary output is an intensity weighted size distribution. DLS is particularly suited for nanoscale particles where Brownian motion is strong, and particle interactions are minimal. It performs best in diluted, well stabilized suspensions.
Laser Diffraction
Laser Diffraction determines particle size based on the angular distribution of scattered light intensity. Larger particles scatter light at small angles, while smaller particles scatter at wide angles. This measurement is interpreted through optical models to estimate particle size distributions.
Literature places techniques like Laser Diffraction in the category of indirect sizing methods, similar in principle to DLS and analytical centrifugation. This context allows a comparison based on what is stated about limitations of indirect techniques, model assumptions, and resolution constraints.
Measuring Principle Comparison
What DLS Measures
- Movement of particles due to Brownian motion
- High frequency fluctuations in scattered light intensity
- Hydrodynamic equivalent diameter based on diffusion behavior
- Sensitivity to microstructural processes such as agglomeration or sol gel transitions
What Laser Diffraction Measures
- Angular patterns of scattered light intensity
- Size distributions derived through optical scattering models
- More directly connected to geometric dimensions than hydrodynamic motion
Both methods rely on optical data and mathematical transformations, but they differ in their assumptions and sensitivity to sample conditions.
When Each Technique Performs Best
DLS Performs Best When:
- Particles are in the 1 nm to 1 micron range
- Samples are dilute and monodisperse
- Hydrodynamic size is relevant for understanding behavior
- Users need rapid, low-cost measurement for submicron materials
DLS is the most popular technique for particle size analysis in the submicrometre range due to ease of use and fast measurements.
Laser Diffraction Performs Best When:
- The size range extends into microns and above
- The sample may have a broad size distribution
- A geometric or volume-based measurement is more relevant
- Concentration conditions are not suitable for DLS
Laser Diffraction’s reliance on scattering at various angles allows it to analyze larger particles and wide ranges more effectively than correlation-based methods.
Strengths and Limitations
Strengths of DLS
- Highly sensitive to nanoscale particles
- Able to detect microstructural transitions and aggregation
- Quick analysis with minimal sample preparation
- Well-developed correlation and frequency analysis models for accurate interpretation
Limitations of DLS
- Restricted to dilute samples due to multiple scattering
- Interpretation depends on model inversion, reducing resolution for polydisperse systems
- Sensitive to unwanted microprocesses like sedimentation and convection
- Outputs hydrodynamic diameter, not geometric size
Strengths of Laser Diffraction
Drawing on the characterization of indirect optical techniques in the provided documents:
- More robust with polydisperse and broad size ranges
- Provides geometric size estimation through scattering behavior
- Can handle higher concentrations than DLS
- Not dependent on Brownian motion
Limitations of Laser Diffraction
- Relies on model assumptions such as optical properties and particle shape
- Lower sensitivity to nanoscale particles
- Requires accurate optical parameters for meaningful results
- May underperform for very fine colloids or aggregated states, where DLS captures microstructural dynamics more clearly
Which Technique Should You Choose?
The decision depends on particle scale, dispersion quality, and the type of information you need.
Choose DLS if:
- You work primarily in the nanometer to submicron range
- You need to understand hydrodynamic motion or aggregation
- Your sample can be diluted without altering its properties
- You need fast, routine quality control for nanoscale materials
Choose Laser Diffraction if:
- Your particles span into the micrometer scale
- Your sample is polydisperse or multi modal
- You prefer geometric size distributions rather than hydrodynamic ones
- You need a technique more tolerant of varying concentration levels
Industry Implications
Modern labs often use both techniques because they complement each other. DLS offers sensitivity to nanoscale behavior and microstructural dynamics, while Laser Diffraction supports larger particle systems and broad distributions. Combined, they allow teams to characterize everything from early-stage nanoparticle synthesis to final product quality in manufacturing.
The ability to resolve fine particle details depends on understanding each method’s strengths, limitations, and assumptions. Making the right choice improves efficiency, reduces measurement error, and leads to better material performance.
Modern Advances in DLS
While traditional DLS instruments are limited by factors such as multiple scattering in concentrated samples, sensitivity to colored or absorbing samples, and challenges with heterogeneous or multiphase materials, new optical configurations and AI driven analysis approaches are beginning to address these issues.
Recent developments integrate machine learning with enhanced optical design, enabling measurements on samples that previously required dilution, modification, or separate preparation workflows. These advances also support improved interpretation of complex distributions and better handling of real-world samples.
Labs interested in these modern approaches can review the Nanopartizer Nanosense device, which incorporates these capabilities:
https://nanopartizer.com/product/
It offers advanced analysis capabilities designed for teams who need precision, repeatability, and intelligent data handling.
References
- Babick, F. (2016). Suspensions of Colloidal Particles and Aggregates. Springer.
Babick, F. (2020). Characterization of Nanoparticles: Dynamic Light Scattering (DLS). Elsevier.