General > General Technical Chat
Tricks of the Trade - knowledge for every day life
Cerebus:
--- Quote from: Kasper on November 01, 2020, 05:52:34 pm ---Pumping hot glue into heat shrink works too.
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Oy! Keep it clean, this is a family friendly forum. :)
Berni:
Oh one more simple one:
PCB cleaner is really good at removing permanent marker marks (The solvent used in permanent markers in generally alcohol based, so no wonder it works so well)
sandalcandal:
--- Quote from: jogri on October 31, 2020, 11:15:19 am ---
--- Quote from: KE5FX on October 31, 2020, 04:50:05 am ---Pro Tip #2: Wear a good pair of sunglasses when performing Pro Tip #1.
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Please don't do this unless you want to experience what permanent blindness feels like. You have no idea if and by how much sunglasses reduce the intensity, and with 405nm being visible i don't think that sunglasses will block it. If you are stupid enough to stare at the spot long enough you will probably fry your cornea, and for what? A faster way of curing epoxy that sucks because you can only hit a tiny spot? If you want it to cure faster get a UV lamp... More power, and it isn't nearly as stupid as using a laser.
Btw, you can get decent laser goggles for 60-70 bucks, and with those you know excatly which part of the spectrum they block to what extend. Using sunglasses because they "block light" is just beyond stupid, those things are absolutely NOT designed to handle extremely strong, collimated light.
PS: Rule No.1 of laser safety: If you can see the laser, you done f**ed up.
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Sunglasses are required by law to block UV, in Australia at least. Even most untinted safety glasses (with "O" outdoor marking) have UV blocking in Australia. Another option cheaper than laser googles are welding googles/lenses which are good enough for low power lasers due to their need to block intense UV radiation and visible light from welding.
Even the lowest shade 1.2 to only allow 0.0003% 313nm UV but 50% 365nm. A shade 5 typical for gas welding only allows a maximum transmittance of 0.0003% 313nm and 0.3% 365nm. Outdoor untinted safety glasses are a maximum transmittance of 0.25% >380nm. Some spectrums for US ANSI welding googles here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5000543/
Edit: For reference 0.3% transmittance is an OD of 2.5. The recommended minimum OD For 200mW 380nm continuous is 2.32 = 0.47% transmittance. https://www.lia.org/evaluator/od.php That's shade 10 and over for visible.
Also not trying to say you shouldn't use appropriate safety gear where required but people are often ignoring readily available and adequate options e.g. using welding googles and instead putting themselves at greater risk. Safety needs to be both accessible and adequate.
KE5FX:
--- Quote from: sandalcandal on November 02, 2020, 10:26:57 am ---Sunglasses are required by law to block UV, in Australia at least. Even most untinted safety glasses (with "O" outdoor marking) have UV blocking in Australia. Another option cheaper than laser googles are welding googles/lenses which are good enough for low power lasers due to their need to block intense UV radiation and visible light from welding.
Even the lowest shade 1.2 to only allow 0.0003% 313nm UV but 50% 365nm. A shade 5 typical for gas welding only allows a maximum transmittance of 0.0003% 313nm and 0.3% 365nm. Outdoor untinted safety glasses are a maximum transmittance of 0.25% >380nm. Some spectrums for US ANSI welding googles here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5000543/
Edit: For reference 0.3% transmittance is an OD of 2.5. The recommended minimum OD For 200mW 380nm continuous is 2.32 = 0.47% transmittance. https://www.lia.org/evaluator/od.php That's shade 10 and over for visible.
Also not trying to say you shouldn't use appropriate safety gear where required but people are often ignoring readily available and adequate options e.g. using welding googles and instead putting themselves at greater risk. Safety needs to be both accessible and adequate.
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I measured a couple of pairs of sunglasses against the ~405 nm LED that comes with the Bondic adhesive kit.
Reference plot (no attenuation):
Ray Ban 8301:
Serengeti Drivers, sadly no longer sold but probably about 1995 vintage:
Normal polycarbonate eyeglasses for comparison:
The Ray Bans exhibit about 3% transmittance at 405 nm, good enough for use with a blue laser pointer IMO unless you plan to aim it directly at your eyes. The Serengetis are OK, too. They have the effect of simulating a pointer that actually meets the rated 5 mW limit.
Bottom line, if you wouldn't use eye protection with a properly-manufactured and marketed laser pointer -- not saying you shouldn't, but I somehow doubt that many people do -- then you don't need to use anything beyond sunglasses with these overclocked Shenzhen specials.
That being said, I'm not crazy about the lack of IR filtering on these lasers. The sunglasses do a good job of cutting down on UV and near-UV transmission, but they aren't as effective at 800 nm. A big chunk of the power output from these pointers is invisible IR, which is arguably more optically-hazardous than the blue light:
Not enough to make me reach for a welding helmet, but it is a bit sobering.
jogri:
--- Quote from: sandalcandal on November 02, 2020, 10:26:57 am ---Sunglasses are required by law to block UV, in Australia at least. Even most untinted safety glasses (with "O" outdoor marking) have UV blocking in Australia. Another option cheaper than laser googles are welding googles/lenses which are good enough for low power lasers due to their need to block intense UV radiation and visible light from welding.
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The problem is that 405 nm doesn't really count as UV, it is just a deep purple... You really have to look at the wavelength, you can't just assume that just because it says UV it will block a laser (and are we talking about UV-A, B or C?). I'm willing to bet that sunglasses don't provide protection against 405nm, just because that would distort the colours. As you have already mentioned, the transmittance increases quite a bit with the wavelength, if you have 50%@365nm, then what do you have at 405? And let me just quote the product safety page of the australian government regarding UV blocking sunglasses:
--- Quote ---The mandatory standard requires that sunglasses must protect users from ultraviolet radiation (UV) within the range of 280 and 400 nanometres.
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405 > 400 nm... And 5 nm can make quite the difference for laser goggles as they tend to have rather sharp absorption edges.
But let's tackle the most important reason why both sunglasses and welding goggles are NOT suitable for lasers: LASERS EMIT COHERENT LIGHT
Both the sun and the arc from a welder won't do that and thus won't even come near the obscene photon/energy densities of a "small" 100-500 mW laser. Combine that with the fact that blue (and probably 405nm) light is by far the most dangerous wavelength for your eyes as it will instantly boil the blood in your retina -> not great. Just to really pronounce the difference between a laser and a "normal lightsource": If i project the full output of my 300 W 30 mm mrad laser at a wall 10m away i will get a spot with a power density of 240 kW/m^2. If i switch on a 300 W lightbulb i will get 1 W/m^2... Same power, yet the laser provides a spot with 10^5 times the power density. The intensity of non-coherent sources correlate with the distance cubed, but lasers don't follow that rule... In that example, the 40mm spot from 10m away just becomes a 130mm spot at 100m.
Blue 445 and 405 nm are just on the edge where the lens of the eye is transparent and where light will get focused on the retina-> tiny spot (the diameter is in the um range as the incoming light is coherent [nature never expected such light in the first place]) with extreme energy density that can already be in the kW/cm^2 range with a 5mW laser.
UV-A to C (380-100 nm) get blocked by the lens, so they don't get focused and can dispense their energy over a wider area (still NOT recommended) as exposure will lead to cataracts.
So should you use welding goggles or sunglasses that where never designed to block neither coherent light nor light over 400 nm to look at a 405 nm laser? Absolutely effing not.
--- Quote from: KE5FX on November 02, 2020, 12:54:17 pm ---The Ray Bans exhibit about 3% transmittance at 405 nm, good enough for use with a blue laser pointer IMO unless you plan to aim it directly at your eyes. The Serengetis are OK, too. They have the effect
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That's a OD rating of 1.something... Aka: A joke, especially with unknown 100+ mW diodes. You really shouldn't go below 4 or 5.
(Sorry for the rant, but saying that it is safe to look at a laser with anything other than proper laser goggles just doesn't sit well with me)
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