Maya Ellison
The transmission of light through plastic depends on various factors, including the type of plastic, its thickness, and the wavelength of the light. Different plastics have varying abilities to transmit light, with some blocking or absorbing certain wavelengths while allowing others to pass through. For example, UV light, which has a wavelength of 365-400 nm, can be blocked or transmitted by specific plastics, whereas shorter wavelengths of around 300 nm or below are typically absorbed by most plastics. The surface texture of plastic also influences light transmission, with rough surfaces scattering light in all directions and smooth surfaces internally reflecting light at grazing angles.
| Characteristics | Values |
|---|---|
| Does plastic let all light through? | No, it depends on the wavelength of light. UV light of ~350-400 nm passes through most plastics, but light of less than ~300 nm is absorbed. |
| How does plastic block UV light? | Thin pieces of plastic are often sufficient for blocking UV light. The energy from UV light may be absorbed and re-emitted as light with a safer energy level. |
| How does plastic reflect light? | Rough plastic scatters light in all directions, while smooth plastic reflects light that strikes at a grazing angle back inside. |
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What You'll Learn
Rough plastic scatters light
The scattering of light by rough surfaces is a well-known phenomenon. When light hits a rough surface, it bounces off in multiple directions, creating what is known as diffused reflection. This is in contrast to specular reflection, where light reflects off a smooth surface at a single angle, creating a clear and defined reflection.
Rough plastic exhibits this phenomenon of light scattering. When light strikes rough plastic, it scatters in all directions, including towards the eye, making the plastic appear illuminated. This is because the light rays strike the rough surface at various points and angles, resulting in diffused reflection.
The scattering of light by rough surfaces allows objects to be seen from various angles without forming a clear image. For example, when light hits a sheet of paper, which has a rough surface, the light scatters, allowing us to see the paper from different angles. This is why we can read text on a page from different angles due to the scattering of light.
In contrast, specular reflection occurs on smooth surfaces, such as mirrors, where the angle of incidence (the angle at which light hits the surface) equals the angle of reflection (the angle at which light bounces off). This results in a clear and defined image, as seen in mirrors or still water.
The scattering of light by rough surfaces can be undesirable in certain situations, especially in optical systems where controlled reflection or refraction is required. In such cases, the surface roughness needs to be limited to control the scattering of light and achieve the desired optical effect.
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Smooth plastic reflects light
The transmission of light through plastic depends on several factors, including the type of plastic, the thickness of the material, and the presence of UV absorbers. Different types of plastic have different transmission spectra, and the formulation of the plastic, including the addition of UV absorbers, can also affect light transmission.
However, when it comes to smooth plastic specifically, it is important to understand how it interacts with light. Smooth plastic has a unique property where it reflects light that strikes its surface at a grazing angle back inside the material. This phenomenon is in contrast to rough plastic, which scatters light in all directions, causing some light to be visible to the human eye.
The behaviour of light reflection in smooth plastics can be observed when light strikes the edge of the plastic at a right angle and escapes, becoming visible. This is why you may see light at the edges of a smooth plastic surface. The reflection and refraction of light in plastics can be manipulated by modifying the surface, particularly the backside of the plastic, to reflect and refract light in specific ways.
While smooth plastic reflects light internally at certain angles, it is important to note that it does not mean that all light is reflected. The transmission of light through plastic also depends on factors such as the wavelength and intensity of the incident light, as well as the refractive index of the plastic material. Different types of plastic have varying abilities to transmit light, and factors like colourants, additives, and impurities can influence their transparency or translucency.
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UV light and plastic
The transmission of light through plastic depends on the type of plastic, its thickness, and the wavelength of the light. UV light, which has a shorter wavelength than visible light, can be blocked by some plastics. However, not all plastics are created equal when it comes to their ability to block UV rays.
UV light can cause significant degradation to many materials, including plastics. This degradation can lead to discoloration, a loss of gloss, and mechanical issues such as cracking. Polystyrene, for example, undergoes rapid yellowing and gradual embrittlement when exposed to UV irradiation in the presence of air. This is due to the production of radicals by oxidation, which cause the polymer chains to break down. Other plastics, such as polypropylene, have a high degradation rate when exposed to UV light.
To prevent UV damage, anti-UV chemicals can be added to plastics during the manufacturing process. These chemicals act similarly to those used in sunscreen, protecting the plastic from the harmful effects of UV rays. This is particularly important for products that will be used outdoors or exposed to sunlight, as prolonged UV exposure can cause the plastic to fail altogether.
The transmission edge for different plastics varies, but it generally falls within the range of 365-400 nm. This means that some plastics may block UV-A rays, which have a wavelength range of 320-400 nm, while others may only block a portion of this spectrum. However, it's important to note that the formulation of the plastic can also affect its UV-blocking abilities, as some plastics may have UV absorbers added to improve longevity.
Overall, while some plastics can block UV light to varying degrees, it is not a universal property of all plastics. The specific type of plastic, its thickness, and the presence of UV stabilizers all play a role in determining its ability to block UV rays.
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Plastic screen protectors
However, one of the drawbacks of plastic screen protectors is their lack of flexibility, making them tricky to install on certain phones. They may also be less durable than tempered glass, leaving devices vulnerable to damage. It is worth noting that low-quality plastic screen protectors can be less environmentally friendly. For those concerned about sustainability, plant-based plastic options, such as the Ultra Eco, are available.
When compared to tempered glass, plastic screen protectors are thinner, lighter, and more affordable. Tempered glass undergoes a unique manufacturing process, involving extreme heating and rapid cooling, resulting in enhanced strength and scratch resistance. This added toughness provides a more secure feel, and its rigidity makes it easier to apply to most phones. However, the increased thickness of tempered glass may be a drawback for some users.
While both options offer impact and scratch protection, the choice between a plastic or tempered glass screen protector ultimately depends on individual preferences and priorities. Factors such as cost, durability, ease of installation, and environmental impact should be considered when making a decision. It is worth exploring the various options and manufacturers, such as ZAGG, to find the best solution for your specific needs.
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Plastic's transmission spectra
The transmission spectra of plastics refer to how plastics interact with light, specifically their ability to transmit, absorb, and scatter light. This property is influenced by factors such as the type of plastic, additives, thickness, and surface roughness.
Different plastics exhibit varying transmission properties in the ultraviolet (UV) range of the electromagnetic spectrum. The transmission edge for common plastics falls between 365 and 400 nanometres (nm). This means that plastics generally start to transmit light in this wavelength range, with some absorbing and blocking UV rays. However, it's important to note that the formulation of plastics, including the presence of UV absorbers, can significantly impact their UV transmission characteristics.
In the visible light range, plastics can also vary in their transmission properties. Some plastics are transparent, allowing a significant portion of visible light to pass through, while others are translucent or opaque, transmitting light to varying degrees. The dispersion, absorption, and scattering properties of light by plastic sheets in this range can be studied to identify and classify different types of plastics, especially in aquatic environments.
Additionally, the transmission spectra of plastics extend into the near-infrared (NIR) region of the spectrum. This region is utilised for studying the optical properties of plastics, such as dispersion, absorption, transmission, and scattering, as well as calculating sample thickness. By analysing the transmission spectrum and refractive index of plastics in this range, it is possible to estimate the average surface roughness of plastic samples.
Overall, the transmission spectra of plastics encompass a wide range of the electromagnetic spectrum, from the UV to the NIR region, with varying degrees of light transmission, absorption, and scattering depending on the specific characteristics of the plastic material.
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Frequently asked questions
No, it depends on the type of light and the type and thickness of the plastic. Rough plastic scatters light that strikes it in all directions, while smooth plastic reflects light that strikes at a grazing angle back inside. UV light of ~350-400nm will pass through most plastics, but light of less than ~300nm would be absorbed.
UV light can degrade plastic and turn it yellow.
PET blocks UV light under 300nm, similar to glass.
If the plastic is designed for sustained outdoor use, it may have UV absorbers in it. If it's single-use plastic, it probably doesn't. You can also look up the material safety data sheet (MSDS) for the specific type of plastic.
Yes, the energy may be absorbed and re-emitted at a safer level in the light spectrum, so it may appear that the UV light passed through the plastic.
