Laser safety calculations for a 1W Blue Laser Pointer
The laser safety calculations and hazard distances reported below were performed with our industry respected LaserBee laser safety software package.
For general laser safety information on laser pointers click here.
For some thoughts on control measures and laser pointer hazards see our laser pointer debate page.
Laser Pointer Specification for Safety Calculations
Technical specifications from a 1W blue laser pointer manufacturer website (the manufacturer is Wicked Lasers in Hong Kong, and the product is their Spyder III Pro Actic Laser):
- Wavelength: 445 nm
- Output power: < 1W
- Beam diameter at aperture: 1.5 mm
- Beam divergence: <1.5 mrad
- NOHD for 0.25sec: 211m
- Required eyewear OD: 4.4+
- Classification: Class 4
Lucid laser safety calculations below are based on the following assumptions:
- Wavelength: 445 nm
- Output power: 1W (this is the maximum value claimed on the manufacturer website, and worst case if the < 1W is believed)
- Beam diameter at aperture: 1.5 mm this is used as the d63 source diameter - a simple approximation.
- Beam divergence: 1 mrad (this is based on typical laser pointer divergence and the manufacturer website claiming less than 1.5 mrad)
Laser Safety Calculation Results:
The Nominal Ocular Hazard Distance (NOHD) is the distance within which, direct exposure to the laser beam is likely to exceed the Maximum Permissible Exposure (MPE). The MPE is the exposure level below which the majority of people should be safe from injury, but if exceeded there is a possiblity of injury which will increase as the exposure level or duration increases.
The NOHD is normally calculated for a 100 second exposure to the most hazardous part of the laser beam. In the case of lasers where the beam is a highly visible laser wavelength, then an accidentally exposed person may be expected to blink and turn away (aversion reflex), with the laser safety standards typically taking 0.25 seconds as a time in which people might be expected to respond. Below we have calculated the NOHD for both the full 100s exposure and the much shorter 0.25s exposure the manufacturer has used:
- NOHD (std 100 sec exposure) = 1.1 km
- NOHD (10 sec exposure) = 355 m
- NOHD (0.25 sec exposure) = 222 m (-this value compares well with that quoted by the manufacturer above)
Extended NOHD
The Extended NOHD is a measure of the distance within which somebody using binoculars or a telescope may be at risk. This may appear an odd parameter, but clearly at some events or in some passtimes and professions binoculars are used.
- ENOHD (100 sec exposure) = 8 km
- ENOHD (10 sec exposure) = 2.55 km
- ENOHD (0.25 sec exposure) = 1.6 km
In the case that a laser is accidentally activated and the beam passes into a persons eye, the exposure duration could, in some cases, be a small fraction of a second, so what would the NOHD be for an exposure of just 1/1000 of a second (1 ms)? The answer is 110 m. The ENOHD for this 1 ms exposure is calculated to be around 800 m.
Distance where 1 ms laser exposure could be 10 times the Maximum Permissible Exposure (MPE)
Some people might argue that not all people are injured as soon as the MPE is exceeded, so what if we take an exposure level of ten times the MPE as a value at which we might expect many people, if exposed to the beam, to suffer an eye injury? In this case we can state:
- Distance within which the laser could exceed the MPE by a factor of 10 with just a 1 millisecond exposure = 32 m.
Clearly, if it is as powerful as claimed, then it is not a trivial laser. Perhaps the biggest problem however is for drivers and pilots. Although Blue lasers are much less visible that Green lasers of the same power (since the eye is far more sensitive to Green in its visible 'photopic' response), when the laser is this powerful it is still capable of delivering significant 'glare' or 'dazzle' effects that can reduce vision. This is similar to on-coming car headlights on main beam, but in the case of powerful visible lasers can be more dramatic with the potential for longer times until the exposed person can see properly again. As with car headlights, this effect is most pronounced at night
Visual Impairment Distances:
The US ANSI Z136.6 standard is currently the only standard we know of that deals with visual impairment, and is explained in the Laser Pointer study. Below we have calculated the Sensitive Zone Exposure Distance (SZED), and the Critical Zone Exposure Distance (CZED) as:
- SZED = 194 m
- CZED = 873 m
These values are corrected for the Photopic Luminous Efficiency of the eye at 445 nm (the laser wavelength), but are not corrected for atmospheric absorption which is a very small correction for distances of less than a km (on most days you can see clearly over a distance of a km, although over much longer distances the view may be hazy due to atmospheric scattering).
Discussion of the Sensitive Zone Exposure Distance
The Sensitive Zone exposure distance (SZED) for this laser is actaully shorter than the NOHD, with this situation occuring because the eye is less efficient at 445 nm, and so there is a the possibility of permanent retinal eye injury at distances greater than the SZED. This is essentially because the eye does not see blue very well, so blue is not a good colour for a laser pointer when the user wants to be able to see the laser beam or incident spot. A green laser of similar specification (power and divergence) would have a shorter NOHD and a significantly longer Sensitive Zone exposure distance.
Skin hazard evaluation:
Skin MPE exceeded in 0.1 second at 2 m. For many people a higher exposure may be required to burn the skin, particularly if the exposed area of skin is not still but is moving (similar to the fact that you would not want to hold your finger in a flame for seconds, but could pass it through a small flame quickly without it burning). It should also be considered that there are quite different skin types, so injury times will be quite dependent on the skin exposed.
Generally we are less concerned with the skin since it can normally recover well from minor burns or injuries, wheras the retina at the back of the eye has much less ability to mend itself and serious retinal burns normally lead to permanent eye damage.
Projector Hazard?
These compact, hand-held, blue lasers are taken out of a home theatre or office projector and re-packaged as a cool toy. Whilst projectors can emit power light levels, the beam is spreading out quickly with distance, so they are only likely to be hazardous to those looking into the projector lens from close range.
By way of contrast, the calculations above show that this compact, toy-like, laser pointer can be extremely hazardous to human eyes over distances of at least tens of metres, or hundreds of feet. Being battery powered it can be used anywhere by anybody.
These calculations are provided for information only and should not be used for other purposes. Lucid Optical Services Ltd does not warrant the accuracy of the values provided.
More general laser pointer safety information can be found here...
These calculations were done efficiently using Lucid's LaserBee laser safety software. LaserBee is an advanced, but user-friendly, software package that helps the novice laser safety user through tips, illustrations and detailed explanations of laser safety issues. For more information and free software downloads click here.