[Study] Optimization of Streetlamps

Yep , that sounds weird. I did not know how to put this study on rails but it comes from a simple observation : a streetlamp look like huge messy light .

In fact, many are optimized for a role-based lighting (parks, roads,city,etc..) but the cost and the city rules seems to constrain the light distribution between strict numbers.

Even if this equipment bring a lot of advantage to our life (like…light.. which is one of the most important thing since 200 years) it bring some problems too. Like light-pollution (well-known by the astronomers) and sleeping disturbance. It’s one of the reason that make spotlight very directional (and the residual light comes from indirect reverberation). [1]

The goal is to define a smart “light-distribution” and find a way to build an optical environment for it. I haven’t any possibilities to test with a real streetlamp or equivalent, so the “concept” part will be simulated on a 3D render software (on a second article).

For now let’s go outside :

A quick observation of streetlamp highlight two things :

  • Although the LED is going to replace the majority of street lightning , a lot of streetlamps are based on multi-directional and monochromatic bulbs.
  • Lighting the road AND the sidewalk , request a highly placed source.

When i observe the city environment (like big city not town), i can say that the most important part of the street are the sidewalk (it’s my personal observation, which is absolutely not scientific). It allow the safety of pedestrian and make a “side guide” for drivers. Even if the cars have headlight, the law (in France), forbid to drive with full headlights (danger of dazzle) so the road need to be lightened too (but lesser than sidewalks). And it exactly the point where , i think, we can work in this study. [2]


Which bring us on the light-dispersion problematic. The draw [3] show the tree configuration of lighting (heterogeneous / road-centered / thrifty) and, on the bottom-right, the ideal distribution (again, just my opinion).

All the challenge will be to build a optical system who enhance the light propagation on the sidewalk , with a noticeable limit near the road and , in the same time, put some light on the road.

All that i will do now , could be simplified if i use a “LED – based” streetlamp, because LED are already directional so all the optical work is useless.

But the complex we do , the interesting it is, so i will use an old good multi-directional light .

With Optogeo-Software (Free) i put a multi-directional light (monochromatic because it’s easier).


My first view will be on the back of the bulb. The goal is to spread the light on the side with the maximum amplitude , without creating an “horizon” (ray > parallel of the ground), which is responsible for light-pollution.

So i put a concave mirror on the top.


We can see that i choose a very wide mirror with a very far focal point.

If the same time, this mirror need to be shaped for managing the side ray. So i go on side view and try with a planar mirror.


Huh..bad idea. The ray are going all over, but i need a directional light on the sidewalk (just under the bulb for example). So i will make it concave (but less wider than in bottom view).


(The shape on the right is the electrical junction of the light-bulb)

We can notice that i add a slight shift between the optical axis and the bulb. It create a ray concentration near the road side. I also add a planar mirror for protecting houses from parasite-lights and improve the sidewalk illumination.

Basically i just need to put a planar mirror on the “road side” for finishing the first template.



(This one have a step before the “road” mirror, but it’s just a test).

My first reaction was : “Hey ..but.. it looks like the actual optical system of street lamps.. ”

Quite true for the side view but the crossing between the “bell” shape of the side and the wide arch of the bottom create an unique shape that i’m exited to try.

But it’s for an another time 😉

(if you work is this domain , i’ll be happy if you can bring your experience and your point of view. I’m totally aware of the savagery of my work , and it’s why outsiders experiences are welcomes)


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