442 nm diodes...

[DZ]

There is definitely a difference. You can't judge it by a picture displayed on a monitor though. Monitor reds are too broad, and their lowest wavelength is around 635 nm. Orange light there just means there's green in it.

If you make any red laser bright enough, eyes see it as shorter wave than it is, it's why the bright spot always looks almost orange due to saturation in the eye. The difference is in details and fades, so long as the eye isn't saturated, there IS a difference between the 660 and 635 nm reds regardless of relative power, and you don't need to put them beside each other to see it. On a monitor, we can kid ourselves that fading the red makes a deeper red, but only because it's not actually capable of a wavelength shift at all. A real wavelength difference is a very different effect. If you add the extra power to the longer wavelength to match apparent brightness of the shorter one, we can still sense the extra power, so the effect seems stronger and deeper, just as extending the bass in loudspeakers does even if the volume is equal, because even at equal volume, more air is moved. The analogy isn't physically exact, but the fact we can even analogise it at all proves that our brains process the different kinds of signals in similar ways.

I never said there wasn't a different between the two. But the photo is just about exactly the way it appeared on the wall, on my laptop display anyway. I'm sure (hope) that most of us here know the effects of saturation. There was no "fading" to create the above effect. Both lasers (660nm Marconi unit and a 635nm Lasever unit) are set to max output (5VDC on the input line) and fed side by side into the scan head. Sure to us we *may* be able to tell a difference between a scan head running 660nm or 635nm, but if you ask anyone watching a laser show if they can tell a difference, chances are the response will be "whats a nanometer?" Even so, at the upcoming SELEM, I think it would be a neat experiment to put up a random display (either 660 or 635nm) and see how many people can tell if its 660nm or 635nm. Then display both for compairison, I think the results might be surprising... With displaying one color and not having the other to compair to, I think some may be fooled...


David

[The_Doctor]

I mentioned details and fades. We perceive that the same, even if there is no actual difference in intensity. It's the same way that old newsprint photos worked, by the ratio of ink to uninked paper. That fine detail appears as a fade or gradient unless you look close. Your spirals do it by a change in density of pattern...

I agree than many people at a show might not know the difference, but experience is on various levels. People at rock concerts will equally go blank if you ask most "What's a phonon?", but they'll nearly all be able to tell you which of their recent nights out delivered the most awesome bass.

People might often be unable to tell 635 from 660 unless they're exposed to these wavelengths often enough. As laser shows become more common, that will happen. I know I can tell. I could even before I was familiar. I'd walk into Maplin to buy bits to make RIAA preamps or for power amp repairs, and I'd see the HeNe laser they put on display, and the light had an odd pinkish quality unlike anything else. Later when it was gone, and they had 67o nm diode modules, and later still, 650 nm, I had an easy time seeing the difference, and it wasn't related only to brightness, there's a real subjective feeling to it. Picking out the 635 nm module was dramatic because it had the same odd orangish/pinkish quality that I remembered from the HeNe that I'd not seen for months by that time. The simplest way I can describe the change is a sense of the red being heavy or light regardless of power.


The main reason I think the difference is important to shows is that only the light reds can be emulated on monitors and TV's. Heavy reds have a power that is transcribed as a light red. It's unfakeable. If you can get a strong heavy red into a show, you have something that can't be faked or copied, you have to be there, you have a spectacle that people will pay to see because there's no other way they can get it. That said, so is the specular effect, that can't be faked by anything either.


Edit: The main reason I can think of for using the shortwave reds and oranges or any other colour in visible range is that the specular effect of monochromatic light is special. It's unfakability is extreme, even mixing red and green monochrome lasers to get orange gets you something that can't have the striking purity and intensity of one monochrome orange. Even with LED's this is true, with lasers, the vividness of a show can depend on it. I think that there are people who are very unobservant, but I think most do see, even if not consciously, it's just a product of the wit we all need to survive activities like crossing roads, or detecting radiant heat sources. We're not always conscious of it, but it's there all the time.

[DZ]

The main reason I think the difference is important to shows is that only the light reds can be emulated on monitors and TV's. Heavy reds have a power that is transcribed as a light red. It's unfakeable. If you can get a strong heavy red into a show, you have something that can't be faked or copied, you have to be there, you have a spectacle that people will pay to see because there's no other way they can get it. That said, so is the specular effect, that can't be faked by anything either.

I'd have to say that I disagree. I really don't believe that more people would come to a show just because its a deeper red. To imply that using 635nm red is "fakeable" just doesn't make sense to me. I fail to see much difference between the 660nm Marconi unit that I've had, the 635nm Lasever unit that I currently have, a 632.8nm HeNe that I have and the 647nm from the Coherent that I've had. The main difference being the more aparent brightness per mW with 635. To be honest, what brings people to a laser show is content. I just went to a laser show at the local planetarium last night and overheard a group of people comment about how they didn't really care about the laser show so much as the 18,000 watt sound system that they use in the theater (which is amazingly loud). Going back to content, I'd put money on the fact that I could draw larger repeat crowds with a 3 color HeNe/60X argon combo with amazing AVI style laser graphics and a kickin sound system than anyone with a solid state white light using 671nm red running a simple home-made graphics show with a Radio Shack sound system....


David

[Dr Laser]

I see the points that all you make. But don't forget we are laser geeks. We see things that 99.9% people will never understand or see. I don't think that lasershows will become so common that more people will see the difference between 635 and 660. Other thing is the price of the lasers. To balance those non standart lasers you will have to give so much more power. for 420 and 660 it's about 4-1-9. ex. 800-Red 200-Green 1.8-Blue. Auch....

[The_Doctor]

Ok, go to the most basic experiment you can, if you've got analog mod and two beams of same thickness and divergence. Project around 50 to 100 mW of 660 and a few tens less mW of 635. Make them parallel, pointing to a white wall. Fill the air with a bit of fog and dim the lights. Adjust the 635 till it looks as near the same as possible. See if you can really make a beam you can't tell apart when looking at the beams, or the spots on the wall. The difference is obvious. It's also something people can pick out seperately in many cases, maybe most cases. I'm sure there are exceptions just as some can't hit the same note twice, not even close, when singing, but these are exceptions to the rule.

I agree about content actually. That's like people go to a gig because they like the music, and the sound system is a secondary thing. On the other hand, in recent demonstrations of the same image on a standard monitor, and on some kind of laser based display, I heard that people were impressed by the depth and brilliance of the colours. It might be that they'd not have noticed if different scenes were on each imager, but red is a broad, huge part of the spectrum, so unless one scene or both lacked reds, they probably would notice. If laser TV's ever take off, you can bet people will become deeply familiar with these effects, even if they limit the wavelength of the red to 635, as it's still deeper than a monitor shows well.

[The_Doctor]

To balance those non standart lasers you will have to give so much more power.

Sure, but that's the way it is. It's the same when balancing frequencies in audio, and just as hard to put precise values on for different powers needed.

With current tech, this is a problem, so that affects price a lot, but while that constraint means there's sense in restricting to brighter, lighter reds, it won't always remain that way. People used to settle for very narrowband speakers and still call them hi-fi, but as magnets got better, and polymers were introduced, people could have deep bass for small money, in their homes. I think lasers will follow the same course, largely driven by the development of laser based TV.


Edit: I went looking on alt.lasers to see if I could find any independent observation that described what I mean, and I found this:

Subject: Frequency vs. Temperature for viz LDs (~635 nm)
From: booatfractalfreakcom (address link neutered by me to stop spambots)
Newsgroups: alt.lasers


Anyone know what the minimum lasing frequency for 635-640 nm LDs is,
based on temperature?

I've got a few pointers based on the SDL-7501 LDs (~15 mW @ 635-640 nm)

I notice the rated frequency is @ 25C.

I recently had a a chance to use the pointer outdoors in very cold
conditions (-12 to -20C) (10 to -5F) and I thought the laser
looked 'orangier'. I left the pointer on for a couple of hours outdoors
in the frigid conditions to let it reach thermal eq. Looked beautiful
on the freshly fallen snow - a brilliant tangy orange. I wonder if it
was under 630 nm.

Since the eye's sensitivity is rapidly increasing in this part of
the visual spectrum, it's possible that relatively small changes
in the lasing frequency are discernable.

Eric

He suggests it's due to a rapid change in the eye's sensitivity in that range of wavelengths, but it's not that. If it were, the difference would be more apparent between deeper reds. In this case it's the increasing change in colour with wavelength, but even so, he's talking about a distinct change in colour that he did not expect to see, without any references to compare with. He also detected it when the wavelength difference could not have exceeded 13 nm, assuming the 0.3 nm per °C, which in the case of the material in red diodes is less; 'Redbelly' answering that post later said it was around 0.15 to 0.2 nm per °C. As the difference between 635 and 660 is 25 nm, we should expect to be able to detect it without difficulty.

[Dr Laser]

If laser TV's ever take off, you can bet people will become deeply familiar with these effects, even if they limit the wavelength of the red to 635, as it's still deeper than a monitor shows well.

You giving the humanity a huge credit. There are not so many people who will see the difference. I work in many clubs and banquette halls. People are there to have fun. Most of them are drunk. If someone there thinking about nanometers and milliwatts my recommendation for him to get some more drinks and talk to the girls. Only place for milliwatts and nanometers is here or on ILDA Awards.... Ohh look at those nanometers they are so beautiful)

[marconi]

Something I have noticed is this:

The ones that just dont care either way

There are those who dont care about the range of colors they could get only that its bright and close enough, or dont or cant notice the difference.

And those who can see the difference dramatically..and care very much about the color gamut.

27nm IS to me a great big difference and I like very much hue–saturation
so I fall in this catagory.

I gave up trying to explain the difference to the first two, sorry

[The_Doctor]

You giving the humanity a huge credit. There are not so many people who will see the difference. I work in many clubs and banquette halls. People are there to have fun. Most of them are drunk. If someone there thinking about nanometers and milliwatts my recommendation for him to get some more drinks and talk to the girls. Only place for milliwatts and nanometers is here or on ILDA Awards.... Ohh look at those nanometers they are so beautiful)

You've missed the point. It's not the geeks with the numbers who see it and the majority who don't, it's the other way round. That's why I saw it before I knew anything much of lasers. That's why the guy who wrote that post in alt.lasers saw it, and went to a source of likely explanations. That's why ordinary people are wowed by the deep reds and sharp blues of a laser-based TV in a tech show.

There's nothing like a bit of knowledge to allow a person to rationalise what they see, to tell themselves what they think is a reason why they should or should not see. Ordinary people do see, though, because they haven't got the same level of stuff in their heads to tell them what they think they should see. And the only reason that the public isn't used to deep reds is that making them in strength for display purposes is expensive, and they don't see many, they mostly compare with TV's and monitors.

Dimiss it all you like, but hiding your eyes behind your hands doesn't make the changing world vanish, it just stops you seeing that it notices your strange self-imposed restrictions. I'm with Marconi, and the rest of the world on this, once you've given your best shot trying to explain, you move on. Can't force a horse to drink...

[DZ]

That's why ordinary people are wowed by the deep reds and sharp blues of a laser-based TV in a tech show.

Ok, this converstion has gotten a bit rediculous... "Laser TV's" and a vector based laser projector are two different things.

There's nothing like a bit of knowledge to allow a person to rationalise what they see, to tell themselves what they think is a reason why they should or should not see. Ordinary people do see, though, because they haven't got the same level of stuff in their heads to tell them what they think they should see. And the only reason that the public isn't used to deep reds is that making them in strength for display purposes is expensive, and they don't see many, they mostly compare with TV's and monitors.

The people who attend laser shows at planetariums or raves or whatever just wanted to be entertained, not educated and really could care less what you are using, so long as it is entertaining.

Dimiss it all you like, but hiding your eyes behind your hands doesn't make the changing world vanish, it just stops you seeing that it notices your strange self-imposed restrictions. I'm with Marconi, and the rest of the world on this, once you've given your best shot trying to explain, you move on. Can't force a horse to drink...

I take this as an offense. To imply that I am somehow close-minded and cut off from reality while using inferior components is upsetting to me. It is clear to me that you seem to lack an understanding of what a good laser show is...

David