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Why we need them?

A Light Diffuser scatters the collimated light from the source to transmit a soft and sober light. While the advent of LEDs has brought about excellent energy efficiency and superior light controls, the point sources present in the LED chip boards pose a challenge for general illuminations in the form of glare. So, the LED light fixtures use specially designed covers that are optimized to offer light diffusion properties. Additionally, these covers serve the purpose of shielding the light source as well. While most LED light diffusers serve the same purpose, they differ in the key materials that they are made of. And, this is where their quality comes into the picture.

Which one is better?

The lighting industry has long been dependant on glass and transparent plastics like acrylic resins for optics design to serve both functional and aesthetic purposes. However, with the advent of LED lighting technology, the necessity for a higher degree of light diffusion has required the development of suitable plastic solutions that do a much better job.

The most commonly found diffusers in the market are made of PMMA- Poly(methyl methacrylate), PS -Polystyrene, PC- Polycarbonate and PP- Polypropylene. Light manufacturers rank the priorities of the properties of these materials to make the best decision.

PS- Polystyrene

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Translucent PS diffuser sheet

Highlights

  • It has good optical characteristics.
  • It is adequately resistant to wear and tear from surface scrubbing while cleaning.
  • It has good chemical and thermal stability.
  • It has high radiation resistance.
  • It resists moisture absorption, making it ideal for humid environments.

Cons

  • It has a low impact strength.
  • It has low weather resistance. Long exposure in outdoor environments makes PS diffusers go yellow and get slightly brittle.
  • Its heat resistance is poor. The deformation temperature for PS is 70-90 °F, making it ideal for environments under 70 °F.
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Prismatic PS diffuser panel

In conclusion, PS has many shortcomings, but for its use in the light guide plate of LED panel lights, its advantages stand out due to its low cost factor. LED panel lights are generally used in indoor environments with a working temperature of about 20-60 °F, thus limiting its climatic influence. Furthermore, it's low cost and a decent light transmission rate of 88%, (less than that of acrylic diffusers) makes it an ideal diffuser for indoor lights.

PMMA- Poly(methyl methacrylate) / Acrylic 

prismatic acrylic diffuser sheet Luxury Photographs Light Diffuser K12 Clear Prismatic Acrylic Light Diffuser
PMMA / Acrylic Light Guide Plate
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Cross-section of a PMMA Light Guide Plate

 Highlights

  • It has a high heat tolerance and strong resistance to UV light, making them yellow-proof.
  • With a light transmittance rate of 92%, it allows for more light to pass through while requiring less power, resulting in higher lumens per watt for the fixtures that use it.
  • Given that lights with PMMA diffusers use less power to achieve higher efficacy, the LED chips don't get overworked.

Cons

  • Its impact resistance is worse than PC but much higher than PS diffusers.
  • PMMA is a slightly costly material in comparison to PS, which drives up the cost of the fixture.

In conclusion, PMMA / Acrylic diffusers offer great performance. Using PMMA as the material for the light guide plate in a flat panel ceiling light means a premium luminaire that is designed to be trouble-free. Its high cost is evened-up by its durability and efficacy.

PC- Polycarbonate

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LED tube light showing its PC diffuser

Highlights

  • It has a high impact strength.
  • It has a high heat distortion temperature.
  • It is resistant to weathering.

Cons

  • It has a relatively low light transmittance relative to PMMA light diffusers.
  • It is an expensive material relative to PS but priced similar to PMMA.

In conclusion, when it comes to durability and stability, PC diffusers are one of the best polymers to rely on, given its high fire-rating and good safety certifications.

PP- Polypropylene

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A pendant lamp with PP diffuser shade

Highlights

  • It is much cheaper as compared to PMMA, PC and PS.
  • Its soft shape allows it to be molded into intricate patterns.
  • It's light transmittance is about 85-90%.
  • Its surface doesn't require filming hence, easier to produce.
  • It possesses good fatigue resistance and impact strength.
  • It has good resistance to electricity and is thus a good electrical insulator.
  • It is more easily repaired from damage.

Cons

  • It is susceptible to UV degradation. Long exposure in outdoor environments makes PP diffusers go yellow.
  • It has high flammability.

In conclusion, PP light diffusers have poor resistance to weathering and are suited more for indoor lights. Given its low cost and PC like optical properties, it is an ideal replacement for PS diffusers.