Mike Murphy's Blog

Laser safety glasses must show some information on what they are supposed to protect your eyes against. This must include the wavelength(s) and the protection levels. These are to ensure that your eyes are fully and properly protected during laser procedures.

This post will explain the markings you should see on our laser safety glasses.

The information in this post can be found in more detail in the European Standard EN207 which conforms to the CE’s Personal Protective Equipment Directive (PPE). All laser safety eyewear must conform with this Directive and must be CE marked in Europe, and UKCA marked in the UK (this Mark will replace the CE Mark).

On most glasses you will find two sets of marking:

1. One set will usually describe the wavelength and optical density ranges;
2. The other set will describe the protection according to the pulsewidths and material damage thresholds.

The photo above shows the wavelength range on the left, with the optical densities (OD) on the right.

The top line – “3199-21108SY” – is a reference number by the manufacturers. It has nothing to do with the safety information.

The next line – “9000-11,100NM   OD>5” – shows that the range of wavelengths from 9000 to 11,100 nanometres is protected to an optical density exceeding 5. This means that the protection level is 10⁵ which is 100,000  (i.e. 1 with five zeroes after it!).

So, what this means is that if you were to fire 100,000 Watts of laser power, within this range of wavelengths, into the filter part, then only 1 Watt would emerge from the other side, towards the eye. In other words, the reduction in power transmission is 100,000 to 1. (Actually, since the specification states OD>5 this indicates that the protection level is higher than 100,000 to 1).

Lasers in this range of wavelengths include the carbon monoxide and the carbon dioxide lasers.

The third line – “10600NM   OD>7” – show a specific wavelength – that of the carbon dioxide laser. The optical density of these glasses at this wavelength is greater than 7. So, this provides a safety margin of 10⁷ which is 10,000,000 to 1.

Now, the more observant of you will have noticed that the line above includes 10,600nm in its range. This is quite typical in many safety glasses. They can have a broad range with a ‘background’ protection OD, with a more specific OD for some particular wavelength, such as here with the CO₂ laser.

The fourth line is – “1064NM OD>10” – the 1064nm wavelength is the fundamental line of the Nd:YAG laser, often used in tattoo removal. These glasses protect to a level of OD greater than 10. That is high!! This is a 10¹⁰ protection level, or 10,000,000,000 to 1. For most commercial Q-switched and picosecond lasers used in tattoo removal, an OD of 7 is quite sufficient.

The next line is – “810-1100NM  OD>7” – this is similar to the second line. It indicates the OD for a range of wavelengths, which includes 1064nm, which is already indicated as OD>10 in the line above. This range covers the diode lasers which typically deliver 800 to 900nm, in the aesthetic field. However, it does not cover the 808nm wavelength, which many aesthetic diode lasers deliver. That is found in the next line…

This is – “770-810NM  OD>5” – which obviously protects the eyes in this range to an OD of greater than 5.

The final line is – “190-420NM  OD>9” – this range of wavelengths is in the ultra-violet part of the spectrum. These glasses have a very high optical density in this range, since ultraviolet light can be hazardous to our eyes. These would be used with excimer lasers.

In summary, this information is relatively simple. It shows the wavelength(s) and the corresponding optical densities.

The information in the second photo gives us more useful information.

The data above conform to the EN207 standard. They use various letters to denote pulsewidths and the maximum energy/power densities which these glasses can withstand.

To explain these markings, I will first describe the meanings of the letters:

D – continuous wave beam (CW) – these are NOT pulsed lasers,

I – Pulsed laser with a pulsewidth greater than 1 microsecond and less than 250 milliseconds,

R – Pulsed laser with a pulsewidth greater than 1 nanosecond and less than 1 microsecond,

M – Pulsed laser with a pulsewidth less than 1 nanosecond

The DIRM letters describe the pulsewidth of the laser. Note that the information in the top photo makes no reference to the pulsewidths, only the optical densities.

LB – this refers to the maximum energy or power density that these glasses can withstand if hit directly with a beam of laser energy. They do not refer to the damage to the laser user.

The numbers after the ‘LB’ are similar to the optical density (OD) numbers above, but they don’t mean the same thing. The numbers against the LB rating must be found from a table in the EN 207 standard.

The optical density of the glasses does not take into account the damage threshold of the filter (and the frame), whereas the LB number does. EN207 dictates that the filter and frame must be able to maintain sufficient eye protection for 5 seconds of continuous power or 50 pulses of energy from a pulsed laser.

The optical density will always be higher than the LB number for any given wavelength range. So, safety glasses with an LB of 6, means that the optical density (which protects the user’s eyes) is greater than 6.

In the above photo, the first line is – “770-1100 D LB 5” – this means that these glasses offer a protection, in the wavelength range 770 to 1100nm, from continuous wave beams (D) with an LB of 5, indicating an optical density greater than 5.

If we look back at the first photo, we see that the range 770-810nm has an OD>5, and in the range 810-1100nm the OD is greater than 7. This corresponds to the LB5 rating (since they are both greater than OD5).

The next line states – “770-810 IR LB 5” – this is more specific than the first line. It tells us that in the range 770-810nm the LB rating is 5 for pulsed lasers with pulsewidths between 1 nanosecond and 250 milliseconds (the pulsewidth ranges for both I and R). Once again, the optical density for this range and pulsewidths is greater than 5.

Next, we have – “>810-1080 I LB 7 + R LB 5” – this is a lot of information for this range of wavelengths. Firstly, in the pulsewidth range between 1 microsecond and 250 ms, the LB rating is 7, indicating that the OD is greater than 7 (which is confirmed in the first photo, with a slight discrepancy in the range 1080 to 1100nm!).

The second part (R LB 5) tells us that for pulsewidths in the range 1 ns to 1 microsecond (typically found in Q-switched lasers) the LB rating is only 5.

So, the full statement tells us that these glasses offer a higher optical density rating for the longer pulses, greater than 1 microsecond up to 250 ms, but a lower OD for pulses shorter than 1 microsecond – for these wavelengths.

The next line – “9000-11000 DI LB 3” – informs us that for continuous beams and in the pulsewidth range between 1 microsecond and 250 ms, the LB rating is quite low – only 3. The OD in this range is greater than 5, as indicated in the first photo. The reason for this is that the OD does not take into account the damage threshold of these glasses – merely its attenuation. The LB3 rating indicates that they would be damaged if subjected to multiple pulses or 5 seconds of continuous power, above that rating. This is where the LB rating differs from the optical density – the latter is protection of the user while the former determines the damage to the glasses.

It should be noted that the OD and the LB ratings are defined in the European Standard EN207, whilst the American ANSI Standard (Z136.1) only discusses the OD (not the LB damage threshold energy/power densities).

“GPT” refers to the manufacturer.

I have no idea what that “S” means here!!

CE is the European conformity mark, which is a legal requirement for all laser safety glasses in Europe.

“1950414” is a big number! It is probably a ‘batch’ or a ‘lot’ number.

The “VLT” refers visible light transmission which is the amount of visible light that passes through the filter. In this case it is 32% which means that 32% of the room’s ambient light can pass through. The higher this number is the more ‘background’ light is available for you to see the patient. If this number is low, then you might need additional lighting to see your patient’s skin and reactions properly.

Summary

Understanding this information will keep you safe, in particular, your eyes. You only have one pair of eyes – look after them!!!

Hope this helps,

Mike.