6 ms·
If it's a 1-micron wavelength laser with a 60 micron radius spot, the divergence can't be much less than about 5.7 mrad half angle. What makes eye safety tricky
by oh_my_goodness 2y ago
If it's a 1-micron wavelength laser with a 60 micron radius spot, the divergence can't be much less than about 5.7 mrad half angle. What makes eye safety tricky is just that 2.5 million milliwatts is a lot of power. Even when you spread it out some.
- cwillu 2y ago‹twitches in metric prefix› 2.5 kilowatts. It's called 2.5 kilowatts. ‹calms down› 2.5 kilowatts is how much power a tea kettle in the UK draws. It's an insane amount of power to pump into a 60 micron point.
- oh_my_goodness 2y ago2.5 billion microwatts.
- TaylorAlexander 2y agoSure but how many millijoules per day is that?
- schoen 2y ago216 billion.
- sebastiennight 2y agoThis seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow.
- maldie 2y agoInteresting what power do microwaves in US deliver. In EU the regular micros are about 900W range give or take 200W (that is 1500W from wall because microwaves are not efficient machines) but kettles have usually range 2200..3000. So it is obvious why everyone uses kettles. I myselft have 3kW one and it heats 0.35 litres to boiling in 51 seconds. To have similar microwave it would have to be 3000W micro that is 4500W from wall and have not seen that kind of monsters, also regular 1 phase EU socket delivers max 3600W so that limits it also.
- cwillu 2y agoStandard wall outlet in the US is 15 amps, so a maximum of 1800 watts. 20 amp outlets (which can supply 2400 watts) are getting common, but I've seen very few home appliances that actually use the extra amperage (as determined by having a plug keyed for such an outlet).
- yencabulator 2y agoA typical US microwave draws 900-1100 watts too. I can't even find a 2000-watt microwave listed for sale in the usual consumer places. That'd be like a "pro chef" level luxury item, likely needing beefier electrical wiring and so on. US electric code requires a dedicated 20-amp circuit for microwave, which isn't supposed to serve a 2000-watt load.
- ClumsyPilot 2y ago> it is obvious why everyone uses kettles. I myselft have 3kW one and it heats 0.35 litres to boiling in 51 seconds. Wh? It’s definitely less hassle, and maybe faster, to fill a cup/mug and stick that in the microwave Than it is to fill a cup, pour that into the kettle, boil it, then pour it back in the cup. Or you have to put more water into the kettle than you need, because you can’t measure it accurateLet, and then it takes longer to boil
- porknubbins 2y agoBrits don’t mess around with tea I guess. I believe they’re mostly on 240v even for residential there. Correct me if I’m wrong but I don’t think it would even be possible to heat water that fast in the US on 120v.
- edscho 2y agoCorrect, it takes about twice as long to boil a kettle in the US. But the US is the anomaly here. Most countries use 220-240V mains like Britain [1]. [1] https://en.wikipedia.org/wiki/Mains_electricity_by_country#Table_of_mains_voltages,_frequencies,_and_plugs https://en.wikipedia.org/wiki/Mains_electricity_by_country#T...
- donw 2y agoTechnically, the US does as well. You have 240 V at the panel, but you only run half for each common circuit.
- grundrausch3n 2y agoTechnically basically all buildings in Germany (residential and commercial) run on 400V 3 phase power. But access to it via sockets is only common in residential homes via sockets in a garage. It gets more common with car charging although they rather use 3 x 230V as far as I am aware of.
- viernullvier 2y agoFun fact: 400V 3-phase and 3x 230V are the very same thing. You'll get 230V AC between Neutral and each of the three phases, but the AC voltage between two of the phases will actually be 400V.
- ponector 2y agoI'm living in apartment block built in 2016 in eastern EU and here every apartment has a separate 3 phase(5 pin) socket for the stove. It is a 7kw beast, it can easily destroy regular aluminum-steel pan if you put it on max heat. Steel part will fall apart.
- ruined 2y agobritish household AC is wild, it's like they've got a full-power american range plug for every outlet
- gambiting 2y agoAnd because nearly every single house in UK is wired for single phase only, your connection to the grid is usually rated at 80-100amps(so a regular British home can draw around ~20kW on a single phase).
- beAbU 2y agoNot just UK, the whole world except North America and Japan. South african plugs are rated 16A @240V. Thats a safe 3.5kW at each and every plug socket in the house.
- cesarb 2y ago> Not just UK, the whole world except North America and Japan. Brazil is also an exception. The standard socket is only 10A (with a 20A alternative for things like air conditioners), and the voltages vary depending on the city (and the building, and location within the building); you might have 110V, 115V, 127V, 220V, 230V, and perhaps others I have missed (I went in more detail about it at https://news.ycombinator.com/item?id=40385851 https://news.ycombinator.com/item?id=40385851). I live in a 127V/220V area, so my single-phase sockets are 10A @ 127V, for a total of only 1.3kW each.
- beAbU 2y agoSo it's pretty normal for a "230v" plug to actually be anything between 220v and 240v. Voltages fluctuated pretty wide depending on location. It's all down to the loca transformers. But mixing 100s of volts with 200s of volts sounds mad. I presume you had the special plug for your 200 range outlets? Does Brazil also have split phase AC like the US?
- cesarb 2y ago
- brianpan 2y agoThe back of the envelope comparison isn't difficult. The energy in different forms are doing the same thing. Doesn't your microwave heat a cup of water in about the same amount of time as a tea kettle? And most tea kettles are bigger than one cup. Now, think about concentrating the same amount of energy to heat up your eyeball. Or worse, concentrated into a tiny point on your eyeball.
- swiftcoder 2y agoI recently bought a 3500 watt electric kettle out of the bargain bin in LIDL, for around 20 euros. Europeans do not mess around when it comes to hot beverages
- nottorp 2y agoYeah funny, i was going to say 2.5 kW kettles are a britishism and the ones on continental europe are weaker... ... but then i checked my eastern european kettle and guess what, it's ... 2.4 kW.
- sho 2y agoIt's actually only americans who unaccountably make do with these horribly underpowered kettles. The rest of the world wants their tea and they want it now...
- gcanyon 2y agoTechnology Connections did an excellent video on this: https://www.youtube.com/watch?v=_yMMTVVJI4c https://www.youtube.com/watch?v=_yMMTVVJI4c tl;dw -- kettles in the U.S. only take about 4+ minutes to boil a liter of water. So when you say "now" you really mean it.
- lupusreal 2y agoI just nuke a mug of water for a minute or two when I'm making instant coffee. I never understood the big deal about electric kettles.
- subpub47 2y agoElectric kettles make it easy to pour for pour over.
- harshreality 2y agoA water kettle lets you consistently heat water to the same temperature (not just boiling, high-end kettles have additional temperature options), regardless of: - Amount of water - Initial temperature of water - Position of water container They also prevent superheated water accidents.
- specialist 2y agoYes and: Kettles are much easier to clean than microwave (interiors).
- Dylan16807 2y agoBoiling water in a microwave does not make the microwave dirtier.
- OJFord 2y agoHigher, that would be quite an extraordinary microwave (probably too high) - 800W to 1kW at maximum typically. (I use mine mostly on the 90W or 180W settings, for defrosting.)
- eru 2y ago> This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow. Almost all household appliances that heat (and specifically heat food or water) will operate at the limit of what your house can supply. So that's about 1800 Watt in the US and about 3500 Watt in most of the rest of the world. It's only natural that you see almost any (heating) appliance cluster around these numbers. (I'm actually not quite sure where you would see 2500 Watt kettles. Perhaps some are deliberately neutered a bit, so that you don't blow a fuse in case you have anything else on that circuit? Keep in mind that in the UK, but not in eg France or Germany, every plug also has its own fuse.)
- ljf 2y agoI found it odd that in the US most home brewers don't use electric, but as you say they are limited by the elements they can use. Here in the UK, my home brew beer set up has a 3000w option - great for boiling 25 litres of water/wort - that said it came with a EU plug with some sort of 'fancy' UK plug convertor. After about 4 years the plug started to get so hot that it melted a socket or two - I found that inside the convertor the connection between the EU plug and the UK was really thin, which was causing it to heat up. I cut off the end of the cable and rewired it to a heavy duty UK plug - it has been perfect since then - and no longer over heats.
- eru 2y ago> I found it odd that in the US most home brewers don't use electric, but as you say they are limited by the elements they can use. Yes, but you still see electric space heaters. And they essentially all also have the same wattage: the limit of what they can get.
- sgarland 2y agoElectric is growing in popularity. It’s not overly expensive (compared to the cost of the gear, anyway) to get a dedicated 30A or 50A 240V circuit installed; or you can brew next to your washer/dryer, since there is nearly always a 240V circuit available there.
- nayuki 2y ago<twitches in metric prefix> 60 micrometres. "micron" is a deprecated irregular word that is unlike every other scaling of the metre.
- subpub47 2y agoEh. At least this one is just a name. I don't know how precise we have to be in a blog post, you know? They're the exact same unit.
- Incipient 2y agoCorrect me if I'm wrong "micron" IS metric (decimal based system) but it's NOT an SI unit?
- sgarland 2y agoListen, our shoe sizes are measured in barleycorns, so we’re doing the best we can to adopt metric in places.
- lightedman 2y agoWhen we discuss laser power, damage begins in the milliwatts range, so those of us in the hobby prefer to state it like that so we can easily give people an idea of how fucked they can be if they treat a laser like a toy.
- amluto 2y agoOn the other hand, 2.5kW of light is not outrageous. It’s not drastically higher than some of the larger theatrical lights. (Not that being in a spotlight is pleasant, but it does not permanently blind the actors.) A lot of this comes down to wavelength. Some wavelengths get focused by one’s eye and can concentrate their power in a small spot on the retina. Other wavelengths will be absorbed before they get to the retina and will therefore deposit their power over a larger area and in less sensitive tissue. It can also make a difference if the light is pulsed.
- ponector 2y agoBut isn't stage light labeled for consumed power, not emitted power?
- jaystraw 2y agothat's what i was going to say. and while you can use barn doors and lenses to hone the throw (the size of the beam on stage) -- it's not collimated like a laser is. even with parabolic reflectors like par cans. we're talking magnifying glass and the energy at the focal point (minus what the air absorbs for a given wavelength etc)
- zettabomb 2y agoAre you sure that's actually 2.5kW of optical power? Non-scientific lights aren't usually rated by optical power, but by electrical power.
- deleted 2y ago[deleted]
- tlb 2y agoI'm not an expert here. But according to https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system (see last paragraph of the intro) the diameter of a laser beam doesn't impose a diffraction limit on the optics it goes through. You still get the angular resolution you'd expect given the entire aperture of the lens even though the beam is only going through a small area of it.