# Has the physics of lasers changed or... **URL:** \ **Category:** Factual Questions\ **Created:** [September 3, 2004, 12:16am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868 "2004-09-03T00:16:02Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [September 3, 2004, 12:16am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/1 "2004-09-03T00:16:02Z")
are they just plain lying? (I think I know the answer to this). Not sure which forum this goes in, so I’ll just start it here. I just saw a commercial for Laser-Straight. Nothing special really. Take a look [here](https://www.drdynamics.com/products/laser/default.asp). They show an extended version of the commercial. In it they say “laser straight even goes around corners” :eek: 😕😕😕 . Since when… In the commercial, they clearly show the laser not only going around a corner, but if you watch, up and over a border on the next wall. There was some small print that said “laser must go corner to corner” but I’m not really sure what that meant. Any ideas on this, or like I said, are they just plain making stuff up? ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [September 3, 2004, 12:22am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/2 "2004-09-03T00:22:50Z")
You hang it on the opposite wall, shining over to the corner. It’s not really going around it. ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [September 3, 2004, 12:53am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/3 "2004-09-03T00:53:37Z")
The thing that cracks me up is they say they use, _ **REFRACTIVE LENS TECHNOLOGY!!!** _ As far as I can tell, that that means is they’re using a lens (_all_ lenses work by refraction) to diverge the laser so that it is less colimated, i.e. less like a laser light and more like any other beam of light. That’s how it seems to climb up the moulding (at least in the commercial I saw.) ---
**Author:** ![bughunter](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bughunter](https://boards.straightdope.com/u/bughunter)\ **Post date:** [September 3, 2004, 1:01am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/4 "2004-09-03T01:01:03Z")
I got a Black and Decker laser “level” as a wedding gift. (Yes, I registered for tools. And camping gear… She let me have the scanner!) Anyway, that laser “level” was a piece of utter crapola. The laser beam emitted was sent thru a cylindrical lens, so that it fanned out in a plane. This was good. But the angle of this plane relative to the level plane was adjustable by rotating the lens. Also good. But there was no way to ensure that the plane of dispersion was aligned with the level plane. Bad. There was also no way to ensure that the plane of dispersion was repeated, even if you could make it level. Very Bad. And, on my “level” at least, the range of adjustment _did not include the level plane_. Extremely Bad. In other words, it was a cheap piece of _merde_. I returned it for some glassware. ---
**Author:** ![beltbuckle](https://avatars.discourse-cdn.com/v4/letter/b/3da27b/32.png) [@beltbuckle](https://boards.straightdope.com/u/beltbuckle)\ **Post date:** [September 3, 2004, 1:13am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/5 "2004-09-03T01:13:03Z")
Yes, most of the consumer laser levels are nothing more than glorified laser pointers. The good ones we used in construction are built much better, and self-level. ---
**Author:** ![theckhd](https://avatars.discourse-cdn.com/v4/letter/t/cdc98d/32.png) [@theckhd](https://boards.straightdope.com/u/theckhd)\ **Post date:** [September 3, 2004, 1:19am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/6 "2004-09-03T01:19:26Z")
I remember seeing that commercial last year sometime and having the exact same reaction **Podkayne**. Though it might’ve irked me more (i complained about it on the phone to a friend for at least 10 minutes) since i’m a Physics/Optics guy. They usually work exactly as **bughunter** stated, using a cylindrical lens to expand the beam in one dimension, making a line. As a side note, most semiconductor lasers (which is probably what’s used in these levels due to their low cost and power consumption) diverge to make a line-like beam because they have asymmetric cavities. Usually a diode laser needs a cylindrical lens to collimate the beam. Most likely the natural divergence isn’t enough to make a useful line, so they include a cylindrical lens to further spread the beam so that you can get a line that fits on an entire wall. If the beam diverges enough, one could hang it on the wall and have a line running “along” the hanging wall and “around the corner” just because the beam diverges in that dimension. ---
**Author:** ![Fr0sty](https://avatars.discourse-cdn.com/v4/letter/f/c67d28/32.png) [@Fr0sty](https://boards.straightdope.com/u/Fr0sty)\ **Post date:** [September 3, 2004, 1:27am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/7 "2004-09-03T01:27:28Z")
Eh, I’m not exactly sure how relevant this is, but I had laser tag guns that bounced off walls and hit each other, unless they really weren’t lasers? I’m not really exactly sure how this works… so I’ll let y’all ponder upon that. ---
**Author:** ![Alan\_Smithee](https://avatars.discourse-cdn.com/v4/letter/a/2acd7d/32.png) [@Alan\_Smithee](https://boards.straightdope.com/u/Alan_Smithee)\ **Post date:** [September 3, 2004, 5:27am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/8 "2004-09-03T05:27:42Z")
As soon as I saw the ad, I wondered how you make the line level. If you can’t do it automatically, it still isn’t necessarily a _total_ piece of crap: you just have to use a regular old bubble level to make sure that your laser level is, well, level. It would still be handy as a replacement for a chalk line, if it otherwise works as well is it appears (which I frankly doubt.) ---
**Author:** ![Alan\_Smithee](https://avatars.discourse-cdn.com/v4/letter/a/2acd7d/32.png) [@Alan\_Smithee](https://boards.straightdope.com/u/Alan_Smithee)\ **Post date:** [September 3, 2004, 5:31am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/9 "2004-09-03T05:31:59Z")
Oh yeah, I almost forgot– > [@theckhd](#): > > If the beam diverges enough, one could hang it on the wall and have a line running “along” the hanging wall and “around the corner” just because the beam diverges in that dimension. I assume you mean that it could go around an _interior_ corner and not, as the ad appeared to demonstrate, an _exterior_ corner (which would require hanging on the opposite wall). ---
**Author:** ![vinniepaz](https://avatars.discourse-cdn.com/v4/letter/v/b4bc9f/32.png) [@vinniepaz](https://boards.straightdope.com/u/vinniepaz)\ **Post date:** [September 3, 2004, 5:36am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/10 "2004-09-03T05:36:27Z")
i remember seeing this commercial and wondering exactly how you are supposed to make it level. its cool and all that its a laser but that doesnt give it some magical properties of levelness… ---
**Author:** ![Jenaroph](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Jenaroph](https://boards.straightdope.com/u/Jenaroph)\ **Post date:** [September 3, 2004, 6:41am UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/11 "2004-09-03T06:41:07Z")
> [@vinniepaz](#): > > i remember seeing this commercial and wondering exactly how you are supposed to make it level. its cool and all that its a laser but that doesnt give it some magical properties of levelness… There are a couple of level bubbles built into it. As **bughunter** explained, if the level and the laser are aligned, you’re golden. If they’re not, you have a shiny toy. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [September 3, 2004, 1:20pm UTC](https://boards.straightdope.com/t/has-the-physics-of-lasers-changed-or/262868/12 "2004-09-03T13:20:33Z")
I have a cheap Black and Decker laser level – it works absolutely perfectly. It auto-levels, so there’s no having to fool around with a bubble level, which seems to defeat the point. It even self levels vertically, too (same beam, just split). One thing that does suck, though, is that the beam doesn’t go in all four directions, so if I need the beam to go left or down, I’m screwed. Or I have to put it in non-auto-level mode, put it upside down, and grab the bubble level. All in all, it was $30 well, well spent!