# Safe Laser displays

I hope this is in the right stack exchange. Here's my question, assuming that all blue lasers are too risky to the eye to risk [using], is it possible to use only low-energy red and green lasers and: blue; green; blue; photo-phosphore-painted transparent diffuse screens; to create a CMYK laser-spirograph based display, that is safe to look [directly] at?

Blue[paint]+Green[laser] = Cyan[dot], Red[laser]+Blue[paint] = Magenta[dot], Red[laser]+Green[paint] = Yellow[dot], background = Key.

I want to experiment with low latency display tech, and need to know how to measure the diffuseness and dangerousness of lasers. Please note: I am an autodidact, so I'm not as smart as a proffesor, but not as dumb as a newb. There are some weird patches in my knowledge gap. After this very important question is answered, I also need to know how to approximately convert RGB color channel signals into their corresponding CMY signals to best reproduce the RGB image.

• Related on EE.SE: Laser - damaging to your eyes? Dec 21, 2017 at 6:40
• It could also be refrased as: "Can an additive CMYK system be realistically used? and what are the maths for converting additive RGB to it?" I know that the light is still behaving like RGB, because its... light. But with CMY light sources, would I still be able represent a broad range of colors? My one question wasn't vague, but it was about 2 things: eye-safety & color/light math (specifically as it relates to: RGB to CMY conversions). Dec 21, 2017 at 10:31
• Cos most questions about "RGB to CMYK" realize that RGB is additive while CMYK is subtractive, but in this case: they are both additive (as the are both a collection of 3 overlapping channels of produced light in this instance). So many of the answers to the usually framing of this question, are unhelpful seeming to me, since they do not address the context of this specific scenario. Dec 21, 2017 at 10:33
• I apologize if there's something in the rules against twofers; I'll try not to do it again, but in this case: I felt it was necessary as an intrinsic supplement to the context. I would rather not break this into 2 seperate questions, but if I am breaking a hard rule: then I am willing to [begrudgenly] do so Dec 21, 2017 at 10:39
• There's also the laser safety thing, but once I can safelylook at my display without [risking the result of] hurting myself [from doing so]; I still need help with: knowing if-and/or-how-to: get the images to display their intended colors (a way to get a reasonably close approximate of their intended [RGB] colors is all I am expecting/hoping-for [from the CMY display device]). Dec 21, 2017 at 10:49

You must consult someone who has a full understanding of ISO/IEC60825-1 2014 and has had training in its implementation as a "Laser Safety Officer". If you work at a university, school or government department, such places employ or have access to the time of a Laser Safety Officer. Only such people are qualified to advise on laser safety.

So my questiom could be clarified/re-phrased as: "what are my options for measuring the 'safeness' of a light-source, in relation to the tolerances of the average human eye?"

Read and understand the specification of IEC60825 "Class 1" in detail; there are no shortcuts and no short answers. The light source must fall within Class 1 if it gets into peoples' eyes, which it clearly does as this is a "display" application, or, if a scanning or wide beam display, Class 1M. If Class 1M, then you must take steps to make sure that only naked laser light reaches peoples' eyes and no viewing instruments are used. Thus a public display rules out Class 1M and only Class 1 is going to be acceptable. IEC60825 gives you details on the measurements you must make. You're going to make a calculation of the level of power and duty cycle (if it's a pulsed source) that reaches peoples' eyes in each wavelength range specified and check that these are within the allowed thresholds of IEC60825.

• I don't work for anybody. I was thinking of doing it DIY with modded consumer laser pointers. I'm not in a hurry however, because I understand that there is a lot that I do not understand. I do not want to break any laws, nor do I want to endanger myself or others; I just to build a cool contraption with a practical purpose Dec 21, 2017 at 5:50
• I was planning on using one of these: " instructables.com/id/Four-Motor-Laser-Spirograph " [ see link about building a four-motor laser spirograph generator ], for every color, and then using a "layered periscope" ("layered periscopes" are an idea I independantly discovered, I'm not sure if they work yet or not) to combine them [into a single "full color" image]. I was planning on using arduino to program ways of converting the color channels into laser intensity and position data, once I knew my display device was: safe to look at. Dec 21, 2017 at 6:00
• So my questiom could be clarified/re-phrased as: "what are my options for measuring the 'safeness' of a light-source, in relation to the tolerances of the average human eye?" Dec 21, 2017 at 6:02
• @user179283 Read and understand the specification of IEC60825 "Class 1" in detail; there are no shortcuts and no short answers. The light source must fall within Class 1 if it gets into peoples' eyes, which it clearly does as this is a "display" application, or, if a scanning or wide beam display, Class 1M. IEC60825 gives you details on the measurements you must make. You're going to make a calculation of the level of power and duty cycle (if it's a pulsed source) that reaches peoples' eyes in each wavelength range specified and check that these are within the allowed thresholds of IEC60825. Dec 21, 2017 at 8:44
• The laser itself, will pass through a screen ( the "painted screen" discussed in the original question posted above) which will ideally act as a "frosted lense" turning that portion of the beam diffuse and no longer specular/coherent; ideally making it safe to put your eye in the direct path of the laser beam. I am just adding clarification, incase this detail changes anything, or increases the ammount of stuff I need to look into. Dec 21, 2017 at 9:39

Generally, laser safety depends on the laser's output power, beam diameter, and wavelength. All of these things are measurable.

But it also depends on what kind of controls are in place to keep the user out of the path of the beam, to ensure the laser power doesn't exceed its normal value, to shut the laser off in case of a fault, how the user is trained, etc. These can not be measured, they simply have to be designed correctly.

• I want it to be idiot-proof, like a television, and to only allow power/amplitude/brightness levels at and/or below the highest safe setting that I am comfortable with, but for it to be capable of modulating the brightness from that value all the way to zero power. I also want it to be reasonably safe for prolonged use. I was thinking I could use/sell/patent it for competitive gaming and other fields if anything came of it. Maybe slap a frenel lense on top of the final-most output, to make a small screen with miniscule beam diameter seem larger, to optimize speed. Dec 21, 2017 at 9:48
• I figure: I could have the beam travel vertically to the side; skip a line on the way down, and repeat until it reached bottom [of the display screen], and then not skip the first line on the way up, travel to the opposite side, skip a line on the way up, and repeat [the last 2 steps] until it reached the top, then: not skip a line on the way down, and then repeat all steps. Like an interlaced video format. A "line" in this case: is defined as: a beam diameter. Dec 21, 2017 at 9:57
• When I say "zero" I mean: "off"/"no power". I feel like clarifying, since sometimes signals are PNP rather than NPN, and I know one is more intuitive than the other. But I still feel the need to clarify that "zero = beam is off" in this instance, since I didn't clarify 10 minutes ago when I originally made my peace. I was refering to the power going into the laser; not the data signal, since the two should usually correlate, but don't neccessarily match (or atleast, that's what intuition tells me, in layman's terms: I am a newb). Dec 21, 2017 at 10:08
• By: "optimize speed", I meant: "optimize the rate at which an interlaced image frame can be drawn, and optimize the rate at which it can be refreshed". It relies [or theoretically relies] on the persistence of vision effect, so it has to be pretty fast, and a smaller draw-screen means less area to cover which means less elapsed time per frame, but perhaps the benefit is miniscule; I plan on researching that after finding the correct safety perameters/guidelines/rules. Better safe than sorry. Safety is always the first step. Dec 21, 2017 at 10:16