Glass Lens vs. Silicone Lens in Street Light

What is the difference between a lens made from optical glass and the lens made from silicon, when used in street light application?

In this blog post, I will explain the pros and cons of both lenses. I will also use a case example to showcase the differences.

The Basics

First let me explain few basic terms related to optics in street light:

Light Pollution

Light that doesn’t go to desired direction and causes harm of anykind. It is wasted light, that isn’t used to its primary purpose. Light pollution can be divided to three different categories:

• Glare

Discomfort glare results in an instinctive desire to look away from a bright light source or difficulty in seeing a task. So as told by its name, discomfort glare causes discomfort.

• Uplight

Uplight can be seen especially in cities: it makes sky glow and stars disappear.

• Light tresspass

Light trespass is found in the vicinity of streets: it can prevent you from sleeping or disturb your garden lighting.

Optical glass

Pros:

• Cheap to manufacture
• Very high temperature range, sensitive also to stress

Cons:

• • Complex optical shapes can’t be done accurately or if the complex shapes are needed, it is expensive
  • Non-optimal light distribution in street light
  • Heavier than silicone (freight costs are more expensive)
  • Lower light transmission than in silicone lenses

 

Silicone

Pros:

• Enables high precision manufacturing of complex optical shapes
• High integration level in luminaire
• Material weighs less than in case of glass lens

Cons:

• Cost is higher than for glass lens

• Lower temperature range
• Lower fire rating

Glass Lens

In the image you can see the light distribution image taken from above. This application uses Glass lens.

• • • Boom angle 15 deg
    • 10880 LED lm, eff 88%
    • Eav 9.0 lx (>9.0 lx)
    • Eav/Emin 2.2 (<4.0)
    • Lv max/Lav 0.3 (<0.4)

Silicone Lens

In the image you can see the light distribution image taken from above. This application uses Stella DWC2 Silicone lens.

• • • Boom angle 10 deg
    • 8400 LED lm, eff 92%
    • Eav 9.0 lx (>9.0 lx)
    • Eav/Emin 2.3 (<4.0)
    • Lv max/Lav 0.3 (<0.4)

Results

Glass lens needs more lumens for the same application. In this case, around 20% more. This means that you generally speaking need more power to get the same amount of light out from the luminaire.

The reason behind the lumen need is the fact that glass lens generates more light pollution. You can see that the trespass light area is much larger in glass lens image (the red box). And on top of this, glass lens distributes light 10 meters away from road. In comparison, silicone lens only distributes 7 meters.

So I think I can end this blog post by stating that the silicone lens gives a lot of advantages over glass lens in street light application.