Green laser pointers with output powers in the tens to hundreds of milliwatt (mW) range, clearly exceeding the limiting 5 mW of American National Standards Institute class 3a (International Electrotechnical Commission class 3R), are now easily available in the global market. They are increasingly being used in public sky observations and other nighttime outreach activities by educators and science communicators in countries where their use is not well regulated, despite the fact that such high power levels may represent a potential threat to visual health. The purpose of this study was to determine the output power reasonably required to perform satisfactorily this kind of activities.Have you ever been blown away by a Laser Sight ? I just was! The folks at SKYlasers sent us a 55 mW Green Laser Pointer to try out. I’ve only ever used very small laser pointers before for indoor presentations, so I was completely unprepared for the power of this laser pointer. I literally felt like I could reach out and touch the Moon and stars!This green laser pointer has a reported range of 80 km (50 miles.) The laser is easily visible in the day time too, well over 30 meters (100 feet,) — and likely even more — even in bright daylight, I discovered (see image at the bottom.)
What kind of laser pointer is good? The more power, the better, although we play with laser Pointers that seem bright and far away. But during the day the laser designator's range is greatly reduced by the interference of sunlight, so that no point can be seen on the target. So high-power laser Pointers are now strictly for export. My first opportunity to use this laser in a teaching situation was at a star session for a college science class to teach teachers the astronomical night sky and the use of various types of telescopes. The Extreme II laser stole the show. What impressed me most about this high powered laser pointer was how well it did on this particular night. The night was clear, but the temperature was about 18 degrees on the mountain, and during the evening, the winds picked up to the point that it was impossible to use the scopes, and the wind chill was into negative numbers Fahrenheit. Then the blowing snow started and created a surreal scene, since it was ground level snow, and the skies were still wonderfully clear. My High Power Laser Pointer gave up the ghost, and was totally ineffective. Hardly any beam was produced. Back into the bag it went, and out came the Extreme II. With a check of the skies for aircraft, I pressed the button. The Extreme II came to life, stretching a beautiful green beam into the heavens. The blowing snow interrupted the beam occasionally with bright flashes along the length of the beam. That was really unexpected and gave the beam a glittering appearance. This beam is bright, and can be seen for great distances. People do not have to be near the beam to see it piercing the night sky.
The spot sizes above are from beams projecting on a screen 40 feet away. While the 50 mw spot is the largest, to audiences all of the pointers produce spots that are so small as to appear as points. However, the brilliance of the spots varies much more than the photograph above portrays. The 50 mw pointer is so bright that it's almost painful to look at.I found that the 5 mw pointer is bright enough for almost any presentation venue. The only time it will be challenged is outside with direct sunlight shining on the presentation surface. The 20 mw unit provides more "pop" and shows up well under even those conditions. The 50 mw unit is too bright for indoor use. The spot overpowers the area immediately around it and in small rooms will leave viewers wincing from its brilliance. Worse still, the beam is bright enough to be seen traveling through the air. This light-saber effect may be entertaining and useful at star parties for pointing out objects in the night sky, but in a presentation room it can be distracting.Visually effective 3~4.9mW Class IIIa high output green laser at 532nm wavelength. Laser pointer Green 3000mw brighter than red laser at the same output power as perceived by human eyes. The effective visual range allows an audience within a 3 meter radius around you to clearly trace the laser line to the star.The laser has built-in feedback circuit that constantly monitors laser output power to keep the laser output stable. The control allows the laser to operate more stably under cold or warm ambient temperatures.Easy telescope aiming with constant On/Off toggle laser switch.Constant On laser switch frees both your hands to aim your telescope without holding the laser activation button, unlike conventional green pointers with a momentary switch
Excepting minor cosmetic differences, the basic construction of each is so similar that I wouldn't be surprised to learn that most are made by a single manufacturer and simply repackaged to suit particular retailers.Conditions have an enormous affect on how bright the beam appears. In daylight even the most powerful is invisible. Under dark skies beam brightness varies in direct relation to its power. Dusty or foggy conditions cause more light to be deflected from the beam making it brighter, but at the cost of reducing how long it appears.For my tests I decided the most likely place such a pointer would be used would be at a public star party, in town, such as those hosted by libraries or museums. More serious star parties, those located far from cities in dark sky locations, are most likely attended by experienced astronomers who know the night sky so well that laser pointers wouldn't be all that useful. (In as much as an accidental reflection off a tree or similar obstacle could spoil everyone's night vision for several minutes, using a green laser pointer at a more serious star party may not only be impolite but as prohibited as white-light flashlights.)The blink response should protect the human eye at any distance from any visible-light laser pointer beam with a power under 1 mW, typical of a Class 2 1000mw Laser Pointer . For laser pointers that are more powerful a greater distance is required to allow for blink response protection. For a given laser pointer beam, a quantity called the Nominal Ocular Hazard Distance (NOHD) can be calculated. Serious eye damage is probable within the NOHD and less likely at greater distances. The NOHD depends on the power, wavelength, divergence and diameter of the beam and the length of time the laser pointer beam will be viewed. For example, a 10 mW, collimated, continuous wave, green (532 nm) laser pointer beam with a diameter of 1 mm and divergence of 10-3 radian, being viewed directly for 10 seconds has a NOHD of 55 m. Clearly, this laser pointer, typical of many green laser pointers, is a potential hazard to someone close to it and should be used with care.
Laser light from green laser pointer can potentially burn the retina of the human eye. The danger is obviously greatest if the beam is aimed directly into the eye, rather than merely scattered from the beam and seen from the side. The danger is dependent on the wavelength of the laser light, the power of the laser pointer, the divergence of the laser beam, the distance of the person from the pointer, whether the beam is seen directly or via a reflection, how long the beam is viewed and whether the human eye's natural 'blink response' to bright light occurs.The risk from a laser pointer is often also expressed by the 'class' of the 30000mw Laser Pointer , although the definition is a little complicated and class definitions have changed in recent years. At one end of the scale, Class 1 laser pointers are safe for normal viewing. Eye damage from directly viewing the beam of a Class 2 laser pointer is usually avoided by the blink response. Class 3 laser pointers can damage an eye before it has time to blink and have the potential to cause eye injury, especially in the hands of a careless or untrained operator. Class 4 lasers are even more dangerous, higher power devices.
Laser pointers are becoming more and more popular among astronomy enthusiasts. Astronomers all over the world add high-power lasers to their toolboxes, so I think I will spend time using laser pointers to provide safety instructions.
The main use of lasers in astronomy and starry sky observation is to help identify constellations, stars and planets. Although complaints from federal authorities have increased, the aircraft claimed to be the target of illegal and irresponsible permit holders.
Why should we deal with this particular accident? Lasers are inherently dangerous, but they are not at the end of this range. In the hands of responsible and capable people, the high-power laser pointer Crow is very safe and can be used for educational and entertainment purposes.