PS52 LASERS, LASER DEVICES and LEDs (revised 2013)
1. Introduction
This leaflet updates CLEAPSS guidance on lasers and LEDs and reflects the widespread retail
availability of semiconductor-based devices.
Optical light from gas lasers and semiconductor light devices is categorised as non-ionising and it
ranges in wavelength from ultra-violet (100 – 400 nm), visible (400 – 700 nm), to infrared (700 – 1000
nm). This guidance note is restricted to devices emitting visible light (400 – 700 nm). See the
separate guidance for devices emitting ultra-violet light.
Lasers and bright LEDs emitting visible light can cause eye and skin damage, depending on the
wavelengths emitted, the intensity of the light and duration of exposure. Light sources that can
cause injury are regulated by The Control of Artificial Optical Radiation at Work Regulations. These
regulations require employers to protect the eyes and skin of employees and others (eg pupils)
from exposure to hazardous sources of artificial optical radiation.
2. Laser safety
All users of lasers in school science should ensure that they are familiar with the guidance given in
the CLEAPSS Laboratory Handbook, section 12.12. The Handbook provides details of practical
activities which are not repeated in this update.
School technology departments now use high–power laser cutters. CLEAPSS publishes a separate
model risk assessment for these devices1 .
Most lasers supplied for school use are now of the semiconductor type. Good-quality devices perform
just as well as their helium-neon predecessors, with the added advantages that they are more robust,
compact and lightweight. They have a longer operational life and their low power consumption means
that some units are battery-powered, avoiding the need for trailing mains leads or portable-appliance
testing.
Lasers are classified to indicate the level of hazard. Lasers sold in the UK should be marked with their
classification according to the current British Standard, BS EN 60825-1:2007 (which is based on the
international standard IEC 60825-1:2007). There are seven classes in this standard, Class 1, 1M, 2,
2M, 3R, 3B, 4. Class 1 is the lowest risk, Class 4 the highest. You may see lasers marked Class 3A,
this is a coding under the older IEC 60825 which is now obsolete and should not be used on new
lasers.
1
Model Risk Assessments for Design and Technology, Laser Cutters, sheet no 1.032, CLEAPSS 2009.
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The USA has a different classification system using Roman numerals instead of numbers: Class I, II,
IIa, IIIa, IIIb and IV. There is no straightforward correspondence between the two systems, but a USA
Class II is equivalent to BS EN 60825 Class 2. Confusingly, in some publications the USA system is
given as Arabic numbers 1, 2, etc. instead of Roman numerals.
CLEAPSS strongly advises that school science departments only use lasers of BS EN 60825
Class 1 or 2. We believe other classes, including 1M and 2M, present an unacceptable risk in the
context of school science.
3. Class 1 laser equipment
Devices which incorporate a laser with beam interlocks and covers, such that accidental exposure is
highly unlikely, are normally referred to as Class 1 laser equipment. A common example is the laser in
a CD player; when the lid or drawer is open, the laser cannot be energised. No attempt should be
made to use lasers previously forming part of other equipment for experimental work. The output
power may be outside the range suitable for safe working in the open laboratory. Also the wavelength
may be beyond the visible spectrum, meaning that the natural aversion responses of the eye do not
function.
4. Class 2 laser
Class 2 lasers have a wavelength between 400 and 700 nm (400 mm is violet, 700 nm is red) and are
limited to a maximum output power of 1 mW. A person receiving a direct eye exposure from a Class 2
laser beam, accidentally or otherwise, is unlikely to be injured because of their natural aversion
response – i.e. blinking and/or looking away. Therefore laser goggles are not required when
operating Class 2 lasers. However, extended direct viewing of the beam may cause harm, so take
precautions to ensure that laser light cannot shine into anyone’s eyes, either directly or by reflection.
Some suppliers cause confusion by advertising laser goggles adjacent to Class 2 lasers in their
catalogues. There is also concern that a few suppliers are offering lasers for school science
investigations with output powers higher than 1 mW. We recommend that schools check catalogue
specifications carefully and that they should not purchase these higher-power devices. You should
specify when buying the laser that it is labelled with the IEC classification, and the supplier supplies
documentation to state the laser is IEC Class 1 or 2.
5. Laser specifications and features for educational use
For reasons explained in section 4, we only recommend the purchase of fully-assembled Class 1 or
Class 2 lasers, from reputable suppliers.
When purchasing a new laser for use in school science, we advise the following.
•
•
•
1
Check that the device (not just the box) is labelled BS EN 60825 Class 1 or 2, as appropriate.
For Class 2 lasers, think carefully before acquiring lasers with wavelengths less than 590 nm
(yellow). 1
For Class 2 lasers, the beam should be narrow, typically 1 mm in diameter when it leaves the
laser, and no more than 5 mm in diameter 4 m away.
The retinal hazard spectral weightings become greater for smaller wavelengths .
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To make the Class 2 laser easier to use or more versatile, the following features/options should be
considered.
•
•
•
•
•
Levelling feet.
A physical means of preventing unauthorised operation should be present. This is usually by
means of a switch with a removable key.
Mounting facility for adjustable slits, diffraction grating, etc.
Modulation facilities - to demonstrate communication techniques and to determine the speed of
light, but a suitable receiver will also need to be purchased. A dual-trace oscilloscope is also
required to determine the speed of light in this way.
Battery - or mains-power supply. Some lasers offer both facilities.
6. Types of lasers NOT recommended for school science use
Class 1M, 2M, 3R, 3B or 4 lasers, or any of the USA classes except Class II.
Laser diode modules.
Any laser that has no classification marked on it.
A laser with no CE mark on it.
7. Laser pointers
Laser pointers are small, pocket-sized, battery-powered, semiconductor lasers, usually operated by a
single push button.
Originally intended for responsible use by lecturers as screen pointers, many products are now
available as novelty items for attachment to key rings or to project amusing images. These have
become widely available very cheaply. Many of the devices have incorrect or no classification labelling
and may have power outputs of well above 1 mW. If you obtain a laser pointer, obtain it from an
established supplier of office/IT equipment, not an unknown supplier on Ebay, etc, and make sure it
has a CE marking and a classification BS EN 60825 Class 2.
Laser pointers are commonly red beams, but pointers are available with green beams and blue
beams. Blue light in particular poses a higher photochemical risk to the eye than longer wavelength
red light. These are a particular cause for concern. Some are arguably not even suitable for use by
presenters because they cause after-images when people view the reflected beam from a projection
screen.
Some laser pointers produce beams that consist of high frequency pulsed light with high peak powers
in each pulse. The manufacturers often quote average power, which can give a misleading indication
of the risk.
8. ‘Home-made’ lasers using laser diode modules
Class 2 semiconductor laser-diode modules can be purchased from various well-known electronic
component suppliers. However, if misused (eg, by connecting the leads to a higher voltage than
specified), the output power of such a module may rise above 1 mW. These devices should therefore
not be used without additional components to prevent misuse. The extra cost, including a case,
dedicated power supply and the amount of time and effort required to design, make and test the
product will be considerable. After construction, the finished unit would need to be checked with a
specialist, calibrated, laser power meter, which is unlikely to be readily available.
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Tel: 01895 251496; Fax: 01895 814372; E-mail: science@cleapss.org.uk; Web site: www.cleapss.org.uk
9. D-I-Y tools incorporating lasers
D-i-y tools with lasers are now commonly available. Package labelling should indicate that these are
class 2 lasers. Most popular are spirit levels, which are able to project lines onto walls etc, saving time
with pencil marking. These tools are designed for building use and are not intended for school
laboratory investigations, however with care they could be used for science activities. If you plan to
purchase such tools, make sure they have a CE marking and a marked classification BS EN 60825
Class 2. We recommend you purchase them from established tool merchants such as B&Q,
Homebase and Wickes etc. We recommend you avoid purchasing them from unknown suppliers
advertising on Ebay, etc.
10.Bright LEDs
In contrast to lasers, LEDs (Light Emitting Diodes) emit divergent, incoherent light. Low output LEDs
(eg a few millicandela) used as indicators on equipment pose no optical risk.
LEDs are now being produced with much greater brightness, particularly for illumination applications.
These LEDs are often called superbright or ultabright, although there is no defined naming
convention. These can cause harm if they are misused. LEDs are classified to indicate the level of
hazard, but with a different classification system to lasers. The classification is defined by British
Standard BS EN 62471 according to the intended use of the LED. There are 4 classes, called
groups:
Group
Hazard
Exempt group
No photobiological hazard
Risk Group 1 (Low-Risk)
No photobiological hazard under normal behavioural limitations
Risk Group 2 (Moderate-Risk)
Does not pose a hazard due to aversion response to bright light or
thermal discomfort
Risk Group 3 (High-Risk)
Hazardous even for momentary exposure
A particular classification may be inappropriate if you use the equipment in different way than for
which it was intended, or use additional optical components to increase the intensity of the light.
Manufacturers of equipment using LEDs in Risk Groups 1 to 3 should label the device accordingly
with product information, eg a notice, caution or warning depending on the risk, but this doesn’t
always happen. For Risk Group 2, you will need to use further safety precautions to avoid exceeding
exposure limits. Risk Group 3 means the device is an eye hazard even for momentary exposure these devices should not be used in school science.
Whatever the risk group, users should not stare at bright LEDs. Note that the Risk Groups 1 and 2
assume reasonable behaviour and that users will have taken note of any warning labels; ie it assumes
that they will look away quickly if the glare is uncomfortable.
If you buy LEDs as components, the risk classification is not always obvious and it may not be
relevant anyway because the proposed use of the LED is not known by the manufacturer. Red, yellow
and green 5 mm and 3 mm LEDs rated less than 5 cd luminous intensity and used at no more than
the recommended forward current are very unlikely to exceed exposure limits values with sensible
use, although if bright enough, they may cause dazzle and after-images if stared at. Particular care is
needed with blue LEDs because blue light has a greater photochemical retinal hazard weighting than
red, yellow or green light. Blue LEDs with a rated luminous intensity under 50 mcd (1000mcd = 1cd)
are very unlikely to exceed exposure limit values with sensible use. Note that white LEDs emit some
blue light. Be wary of buying specialised very high intensity LEDs, LED modules and arrays because
these may exceed exposure limit values without the use of additional precautions.
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© CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ
Tel: 01895 251496; Fax: 01895 814372; E-mail: science@cleapss.org.uk; Web site: www.cleapss.org.uk