Tuesday, October 11, 2011

Comparing Sunglasses to Laser Safety Glasses

I recently posted about the absorption properties of sunglasses, and Jonathan Livengood asked about how sunglasses compare to laser safety glasses. Since I had three pairs of laser safety glasses sitting around in the lab I decided to scan them and show how they compare here.
This image contains the three sunglasses that I showed in my previous post (the black, red and pink lines) and with it I have included the three laser safety glasses (dark, medium and light blue lines). The first thing to note here is that the sunglasses block out light across the visible spectrum (from ~400 to ~720 nm).

For example, the sunglasses that block the most light (the black line, and picture 4 below), and in particular absorb a lot in the blue part of the spectrum (400-500 nm) and therefore they appear to have a slight green tint to them. They also let in less than 10% of the total light. The other pair of good sunglasses (picture 5) also let through less than 10% of the total light. Even the little kid's sunglasses (picture 6) only let through ~30% of the total visible light. Compare this with the laser safety glasses which may allow between 10-80% of the light through depending on the type. Of the three kinds here they let through approximately 30%, 50% and 80% of the visible light. So if you are looking to use laser safety glasses as sunglasses, I would advise against it, they aren't made for it.

The purpose of laser safety glasses is to block out specific wavelengths but allow in as much light as possible in other wavelengths so that you can still see and work in a dark room. The three pairs of glasses here are mostly designed to work with HeNe lasers which have their strongest visible peak at 633 nm, or other red lasers (the lightest colored glasses have a very strong absorption peak further into the infrared, which corresponds to another mode of the HeNe laser).

As for cost, I have no idea what the three pairs of sunglasses cost that I have shown here but I would venture a guess that the two good ones cost between $20-$30, while the kid's sunglasses run about $6-$10 per dozen. So cheap and dangerous. I don't know how much these pairs of laser safety glasses cost, but they typically run from $140 to $300. The reason for this is seen in the tight peaks of absorption around specific wavelengths while letting in as much light as possible in other wavelengths so that you can still see to work. Also you have to buy a different pair for each type laser you are working with since what works for one type of laser will not work for another. This is why science is not cheap.
Pic. 1: Darkest laser safety glasses. Dark blue line in graph.
Pic. 2: Medium laser safety glasses. Medium blue line in graph.
Pic. 3: Lightest laser safety glasses. Light blue line in graph.
Pic. 4: Dark Sunglasses. Black line in graph. I found these in the lab. I have no idea how much they cost, probably about $25.
Pic. 5: Biker Sunglasses. Red line in graph. These belonged to my brother. He bought them in high school. I don't know how much they cost, probably about $25. 
Pic. 6: Kid's sunglasses. These cost about $6/dozen.


  1. So that's where those sunglasses went. :) I don't remember how much they cost either but they were definitely less than $20; probably closer to $10.

  2. Hey! I have your sunglasses! Just so you know...


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