As the radiated output power of individual LED chips
and multi-chip LED arrays continues to increase, more and more people are beginning to pay attention to whether this is also causing more and more damage to the eyes. (Note 1) Of course, most LEDs are completely safe and do not cause any harm to the naked eye. However, there are also many people who are staring at the brake lights of the car in front, or when they are too close to the conference free gift - LED key ring, they will still be dazzled by LEDs. Andrew Dennington, who recently presented a series of optical design techniques at the LED seminar in the UK, warned: "The latest generation of LEDs is not safe, and high-power LED products can hurt people's eyes," he warned. â€œPlease check if the product meets the relevant standards when using it.â€ Another question that comes with LED safety is: Is LED classified as a laser or a luminaire? No matter which category you have, there are both advantages and disadvantages. See how LEDs are used.
First, the laser safety standard
So, what are the current standards for LEDs? The most important one should be IEC 60825-1 issued by the IEC (International Electrotechnical Commission), which is EN 60825-1 adopted in Europe. This standard is known as the laser safety standard, but it is extremely important that it also covers the LED (at least for now) and treats the LED as a laser. Until now, few people have realized that there is such a legal requirement (Note 2): According to 60825-1, LED products need to pass the test in Europe. However, as LED performance continues to increase, related awareness is also strengthening. In the United States, the situation is different. Laser products in the United States are subject to the Federal Decree 21 CFR 1040.10, and if they meet the 60825-1, they are also qualified, but LEDs are not included here. This is because the United States believes that all LEDs are safe, whether it is correct or not! The 60825-1 grades the AEL (Processable Radiation Limit), which is used to indicate the risk of laser or LED light. Level 1 is a safety definition and most LED products either belong to level 1 or do not have to be rated. LEDs and laser products are not subject to 60825-1 if they do not exceed the AEL Level 1 luminosity under all conditions of operation, maintenance, service and failure. The 60825-1 standard is generally quoted in the product itself, not as a packaged LED or as a module within the product. Robert Wells, a Lasermet test engineer at the Expert Test Board, said that additional focusing or parallel optical design of the LEDs would dramatically change the risk of a single LED, or it could define the final product at a completely different level than the LED. The product can be self-declared (that is, tested in the laboratory) or properly tested by companies such as Lasermet and Laser Optical Engineering, another specialized test room for LED testing in the UK. Although an inexperienced tester may make a great mistake, it is also possible to declare the product a level 1 if the product is indeed very dangerous. There are no external agencies that conduct legal compulsive testing of products in this regard.
Second, the LED is classified as a light fixture?
The International Standard Lighting Commission classifies LEDs as luminaires, defined as ductile (rather than point) sources that typically have a broad divergent beam. In general, the way CIE and IEC treat the same product (lamps or lasers) produces different results. TC6-55, Technical Committee 6 of the CIE (Photobio and Photochemistry), is considering different ways to assess the photobiosafety of LEDs.
3. What needs to be defined?
The optical output power of an LED source is indeed important, but it is also necessary to measure the external dimensions of the source rather than the beam diameter. "What matters is the size of the image on the retina, because the image size is inversely proportional to the power intensity," explains Robert Wells. â€œWe have to measure the external dimensions of the source and accurately calculate where it is located.â€ This can be done in a variety of ways, including building an optical system model and using a CCD imager. The classification of the light source is based on the most dangerous conditions that can be reasonably foreseen, although this may also represent a situation that is simply impossible. "For most LED products, using a magnifying glass can be the most dangerous situation," Wells said.
Note 1: What kind of damage does the LED bring? Lasers and LEDs produce a thermal heating effect that is proportional to the brightness of the illuminator, which can cause damage to the retinal tissue. Shorter wavelength radiation produces a photochemical reaction in the retina that changes the chemical composition of the cell. IEC 60825-1 has dual limits of 400 and 600 nm (thermal and actinic aspects). At shorter wavelengths below 400 nm, a large amount of UV light is absorbed by the cornea and/or lens, which in turn can cause damage.
Note 2: Legal requirements. In Europe, the low-voltage guidelines require products ranging from 50 to 1000 volts to meet the 60825-1 standard.
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