Basics of light reflection
- 1. www.micomlab.com www.micomlab.com Gloss Haze Distinctness of Image (DOI) Reflected Image Quality (RIQ) RSpec What is Gloss?
- 2. www.micomlab.com Basics of Light Reflection 3 categories of reflections: Specular / Scattered / Diffuse Specular reflection Mirrors, perfectly polished metals Incoming and outgoing beams have the exact same angle. 3 categories of reflections Scattered reflection Most materials fall into that category Even if most of the light is reflected in the specular angle, surface defects will scatter the ligh creating a bell curve deflection. The bell curve shape will depend on the microtopography of the surface. Diffuse reflection Best example; White paper. Also called Lambertian reflection. Extreme case of scattered reflection where light is reflected in all directions with an isotropic distribution. 1 2 3 O1 O1 O1 O1 O1 O1 O1 O1 O1 O1
- 3. www.micomlab.com Gloss First Glossmeter (Glarimeter): 1914 Well known and widely used Glossmeters measure the ‘shininess’, brightness (quantity of the light directly reflected from the surface) High gloss makes products visually appealing (Automotive, electronics, high end products) 20° 60° 85° Most used angles: 20° (70+ GU) 60° (10-70 GU) / 85°(10 GU) LIMITATIONS Not sensitive to effects which reduce appearance quality Unable to mimic the human eye perception of the surface! The human eye evaluates much more that the shininess of the surface…
- 4. www.micomlab.com Retina Lens Rods Rods Cones Optic Nerve What’s New? 2 products with similar gloss can look very different… why? Gloss is definitively part of the answer. However, 2 products with similar gloss can look very different…why? Distribution effect is the key In a glossmeter, the entering light is treated as one single value, the distribution effect (variation) is not taken into account (like it would be in the human eye). Beam is treated as a specular reflection. Nowadays, equipment with light sensor arrays allow us to take measurements that mimic the light reflection on the human eyes cones. Three Basic Forms of Reflection A - DIFFUSE B - MIXED C - SPECULAR Human eye Incorrect reading Correct reading Array of light sensors Array of light sensors
- 5. www.micomlab.com What’s New? What are the parameters this new technology allows us to quantify? Haze DOI (Distinctness Of Image) RIQ (Reflected Image Quality) RSpec (Smoothness quantification) Even more acurate Gloss values!
- 6. www.micomlab.com Haze Haze HazeGloss 20°-0.9°-2.7° +2.7°+0.9° Specular angle Haze is sometimes compared to “turbidity” Without Haze Surfaces without haze show a deep reflection and high reflected contrast. With Haze Surfaces with haze can be seen as “milky” or “blurry”. Haze is produced by imperfections/irregularities on the surface that affect the light distribution around the specular angle.
- 7. www.micomlab.com DOI DOI measures the Distinctness Of Image: how clearly an image appears on a reflective surface. A low DOI indicates image distorsion (perfect mirror has a DOI of 100) DOI quantifies the “sharpness of the image A low DOI can be seen as the result of a high haze Haze increases / DOI decreases Distinctness Of Image
- 8. www.micomlab.com RIQ Samples 5 to 10 above show similar DOI results but RIQ measurements provide discriminant data. Reflected Image Quality RIQ Reflected Image Quality is an improved version of the DOI RIQ provides a better response to orange peel effects on a wider range of materials and textures. For low gloss surfaces or on samples with low orange peel , RIQ provides results even more in accordance with our visual perception (compared to DOI)
- 9. www.micomlab.com RSpec RSpec is the Peak Specular Reflectance at ± 0.0991° around the specular angle. This very precise measurement quantifies the surface texture as any wave or ripple on the surface will create light diffraction and therefore affect the “light response’. Perfectly smooth surface: RSpec value = gloss value Uneven/textured surface: Rspec value drops RSpec value Gloss value Peak Specular Reflectance Same paint applied on 2 different surfaces Which one would you choose?
- 10. www.micomlab.com Case Study 4 “similar samples” 4 similar samples were evaluated against each other Identifications: Plate 1 / Plate 2 / Plate 3 / Plate 4 Gloss measurements on 24 specimens of each samples Similar values: Non discriminant parameter Plate 2 is less glossy: “rejected” Plate 1 Plate 2 Plate 3 Plate 4 Initial color measurements (similar)
- 11. 10 www.micomlab.com Case Study Haze measurements on 24 specimens of each samples Ideal value: 0 Best contrast DOI measurements on 24 specimens of each samples Ideal value: 100 Best reflection
- 12. 11 www.micomlab.com Case Study Samples performance: ++ : Excellent performance / results -- : Poor performance / results Gloss Haze DOI Sum Plate 1 + + -- 0 Plate 2 - - -- -4 Plate 3 + ++ ++ +5 Plate 4 + -- -- -3
- 13. 12 www.micomlab.com Gloss Haze DOI Sum Plate 1 + + -- 0 Plate 2 - - -- -4 Plate 3 + ++ ++ +5 Plate 4 + -- -- -3 Case Study Plate 3 Plate 4 Plate 1 Plate 2