Haze (optics)

Key takeaways

Haze (optics) belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Haze (optics) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Haze (optics) from memory before moving on to harder problems.

Reference excerpt

There are two different types of haze that can occur in materials:

Reflection haze occurs when light is reflected from a material. Transmission haze occurs when light passes through a material. The measurement and control of both types during manufacture is essential to ensure optimum quality, acceptability and suitability for purpose of the product. For instance, in automotive manufacturing, a high quality reflective appearance is desirable with low reflection haze and high contrast whilst in packaging clear, low haze, highly transmissive films are required so that the contents, foods etc., can be clearly observed.

Reflection Haze Reflection Haze is an optical phenomenon usually associated with high gloss surfaces, it is a common surface problem that can affect appearance quality. The reflection from an ideal high gloss surface should be clear and radiant, however, due to scattering at imperfections in the surface caused by microscopic structures or textures (≈ 0.01 mm wavelength) the reflection can appear milky or hazy reducing the quality of its overall visual appearance. Causes of this could be due to a number of factors –

Poor dispersion Method of applying the coating Variations in drying, curing or baking Types of materials used in the formulation Polishing or abrasion A high gloss surface with haze exhibits a milky finish with low reflective contrast- reflected highlights and lowlights are less pronounced. On surfaces with haze, halos are visible around the reflections of strong light sources.

Measurement Measurement of reflection haze is primarily defined under three International test standards:

ASTM E430 ASTM E430 comprises three test methods: Test method A specifies a 30° angle for specular gloss measurement, 28° or 32° for narrow-angle reflection haze measurement and 25° or 35° for wide-angle reflection haze measurement. Test method B specifies a 20° angle for specular gloss measurement and 18.1° and 21.9° for narrow-angle reflection haze measurement. Test method C specifies a 30° angle for specular gloss measurement, 28° or 32° for narrow-angle reflection haze measurement and 15° wide-angle reflection haze measurement.

ASTM D4039 Test method specifies gloss measurements to be made at 20° and 60°, the haze index is then calculated as the difference between the 60° and 20° measurements.

ISO 13803 Source: Test method specifies a 20° angle for specular gloss measurement and 18.1° and 21.9° for narrow-angle reflection haze measurement. All test methods specify that measurements should be made with visible light according to CIE spectral luminous efficiency function V(λ) in the CIE 1931 standard observer and CIE standard illuminant C. As most commercially available glossmeters have gloss measurement angles of 20°, 60° and 85° haze measurement is incorporated at either 20° (ISO 13803 / ASTM E430 method B) or at 20° and 60° ( ASTM D4039). There are however some manufacturers that offer glossmeters with measurement angles of 30° and haze measurement in accordance with ASTM E430 Method A and C but are fewer in number, therefore for the purposes of detailing haze measurement theory only the first three methods will be included.

ISO 13803 / ASTM E430 method B Both test methods measure specular gloss and haze together at 20° that means light is transmitted and received at an equal but opposite angle of 20°. Specular gloss is measured over an angular range that is limited by aperture dimensions as defined in ASTM Test Method D523. The angular measurement range for this at 20° is ±0.9° (19.1° - 20.9°). For haze measurement additional sensors are used either side of this range at 18.1° and 21.9° to measure the intensity of the scattered light. Both solid colours and those containing metallics can be measured using this method provided haze compensation is used (as detailed later).

ASTM D4039 This method can only be used on nonmetallic materials having a 60° specular gloss value greater than 70 in accordance with ASTM Test Method D523 / ISO 2813. Haze Index is calculated from gloss measurements made at 20 and 60 degrees as the difference between the two measurements (HI = G60-G20). As measurements of specular gloss depend largely on the refractive index of the material being measured 20° gloss will change more noticeably than 60° gloss, therefore as haze index is calculated using these two measurements it too will be affected by the refractive index of the material. Evaluations of reflection haze using this test method are therefore confined to samples of roughly the same refractive index.

Haze compensation The colour (luminous reflectance) of a material can greatly influence the measurement of reflection haze. As colour and haze are both components of scattered light (diffuse reflectance) they must be separated so that only the haze value is quantified; this is also true for metallics or coatings containing metallic pigments where a higher scattering exists. As test method ASTM D4039 is only suitable for nonmetallic materials of more or less the same refractive index separation of the colour and haze components is not detailed. Haze index calculations and measurements using this test method will therefore produce higher haze results on brighter coloured materials than darker with the same level of haze present. The chart below shows these differences for various colours:-

Both ISO 13803 and ASTM E430 method B require a separate measurement of luminous reflectance, Y, to calculate compensated haze. The tri-stimulus value Y gives a measure of the lightness of the material as defined in ISO 7724-2 requiring a 45°/0° geometry to be used with standard illuminant C and 2° observer (although it is mentioned that slightly different conditions will not result in significant errors). Luminous reflectance measurements, Y, are required on both the sample material and a reference white; ISO 13803 details the use of a BaSO4 standard - barium sulphate, a white crystalline solid having a white opaque appearance and high density as this material is a good substitute for a perfectly reflecting diffusor as defined under ISO 7724-2. Compensated haze can then be calculated as - H Comp = H Linear – Y Sample / Y BaSO4 Using the ISO / ASTM method therefore to measure luminous reflectance produces a reliable measurement of Y for non-metallic surfaces as the diffuse component is lambertian, i.e. it is equal in amplitude at all angles in relation to the sample surface.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Haze (optics)

Start with the simplest possible case. Write down what Haze (optics) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Haze (optics) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Haze (optics) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Haze (optics)

In research: Haze (optics) appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Haze (optics) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Haze (optics) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Optical phenomena, so understanding it makes those chapters shorter.
In everyday life: Look for Haze (optics) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Haze (optics) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Haze (optics) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Haze (optics) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Haze (optics) in simple terms?

There are two different types of haze that can occur in materials: Reflection haze occurs when light is reflected from a material. Transmission haze occurs when light passes through a material.

Why does Haze (optics) matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Haze (optics)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Haze (optics).