Characterization of LED-based hybrid diffuse reflectance spectroscopy method for determination of SPF and UVA-PF in blinded multi-centre study (ALT-SPF).

Summary

In a blinded multi-centre ring study, LED-based HDRS delivered SPF and UVA-PF estimates with acceptable bias and, after refinement, markedly improved reproducibility and inter-laboratory variability. With just 10 volunteers and bias correction, SPF results were within 11% of the reference reproducibility limit and UVA-PF met acceptance limits in most criteria, indicating precision comparable to ISO 24444/24443.

Key Findings

• Blinded multi-centre study on 64 samples (with a 16-sample re-evaluation) showed acceptable bias and improved reproducibility after method refinement.
• Using n=10 volunteers and bias correction, SPF results were within 11% of the gold-standard reproducibility limit; UVA-PF met acceptance limits except one criterion nearly met.
• Overall precision was comparable to ISO 24444/24443, supporting LED-HDRS as a viable non-invasive alternative.

Clinical Implications

If adopted by regulators, LED-HDRS could limit erythema-based testing, reducing volunteer exposure and enabling more frequent, precise SPF/UVA-PF verification across product lifecycles, improving consumer protection.

Limitations

• Initial reproducibility and inter-laboratory variability were suboptimal and required method refinement.
• Small number of volunteers (n=10) in re-evaluation; broader skin types and product categories warrant testing.

Future Directions

Standardize HDRS protocols across devices, expand validation to water resistance and diverse product groups, and pursue regulatory qualification as an alternative to ISO 24444/24443.