Red Beam

[ZRTMWA]

First off if any of you have been watching the Blu Ray section you've probably seen a similar thread. I'm wandering the same question. How many mW's of red would equal the visibility of a 200mW green (what is the ratio) ? I searched but only went a few pages back, plus this question is kind of specific. Thanks.

Edit: 100th post!! woot!

 

[NathanF]

First off if any of you have been watching the Blu Ray section you've probably seen a similar thread. I'm wandering the same question. How many mW's of red would equal the visibility of a 200mW green (what is the ratio) ? I searched but only went a few pages back, plus this question is kind of specific. Thanks.

Edit: 100th post!! woot!

Amusingly enough, I came to this forum and just registered to ask this very same question.

I currently own a 50mw cheapie laser that I got off of Amazon marketplace. I use it for astronomical pointing, and it works great, trouncing just about every other green laser that I've ever come across.

My question is this: How powerful of a red laser do I need to get to equal the beam visibility of my 50mw green laser when star pointing at night? (Keeping in mind that the green laser is probably more like 35mw given its price.)

Thanks.

 

[jeffd]

You pretty much arent going to be able to find a red pointer that is comparable in brightness to that power green. I have a 300mw red and it is about as bright as a 5mw green.

 

[ZRTMWA]

But is there at least a ratio so I know? The answer in the blu ray section was 1 green: 4 blu ray, so 200mW of green is about 800mW of blu ray which also would be very hard (or impossible at least now) to find.

 

[Doofus]

I've been told it's about 8x. 8 times the power of a red to equivalent green in visibility. This might be myth, but it's what I've heard for a while :S

I've also heard 60 times, but that's kinda crazy.

 

[nikokapo]

I've been told it's about 8x. 8 times the power of a red to equivalent green in visibility. This might be myth, but it's what I've heard for a while :S

I've also heard 60 times, but that's kinda crazy.

False.

I now have a >200mW red and it's in no way as bright as a 30mW green.

 

[ElektroFreak]

It would take at least several watts of short wavelength red laser light (635nm or less) to equal a 50mW green, and I'm not even completely sure about that. Rayleigh scattering has no effect on longer wavelengths (500nm and up).. 60 times sounds about right, maybe even a little low.

 

[Doofus]

nikokapo I'm just going to assume you meant >200mw RED not green.

Yeah elektro, I started really lookin at it, 60 actually sounds more correct now, haha.

 

[ZRTMWA]

Wow, I thought blu ray was harder to see than red. Thinking of that thread about what colors seem more visible to you.

 

[ElektroFreak]

Referring to a chart of human sensitivity will lead you to believe that, but those charts don't take into account Rayleigh scattering of laser beams..

 

[RA_pierce]

Asking about BEAM visibility is different than asking about SPOT visibility.
Like ElektroFreak said, Rayleigh scattering should be taken into account at shorter wavelengths. Longer wavelengths are not scattered by the air as much.

I have a 300mW 650ish. The spot is about equal in brightness to a 25mW green.
With a beam diameter of about 1.5mm for both, beam is also about equal brightness. The green is a little brighter.
The spot of a 150mW violet is slightly dimmer than both, but not by much.
The beam is brighter than the red beam in darkness.

You also have to take into account that everyone sees these colors slightly differently and not all laser diodes produce the same wavelength. It could be possible that a blu-ray or red diode could output a slightly longer or shorter wavelength.
In the blu-ray's case, shorter would be dimmer and longer would be brighter (vice-versa for red).

Also, our eyes can't focus on ~405nm which makes the beam seem fatter and fuzzy...

But I have made a pretty good white with 20mW Green, 290mW red, and 160mW violet.

 

[NathanF]

You pretty much arent going to be able to find a red pointer that is comparable in brightness to that power green. I have a 300mw red and it is about as bright as a 5mw green.

Well, thanks for the info. At least I know now, rather than wasting my money futilely.

 

[millirad]

And it takes a kilo-watt of 808 IR to equal the brightness of a 50mw green, but that's the last thing you'll ever see.

 

[ZRTMWA]

I have a 300mW 650ish. The spot is about equal in brightness to a 25mW green. With a beam diameter of about 1.5mm for both, beam is also about equal brightness. The green is a little brighter.

Are you saying that the beam of you're 25mW green is equal to or a little brighter than your 300mW Red? That would mean about 2400mW of red or a little bit more would be needed (if my math is right) to match a 200mW green? If so, then matching the beam is totally feasible.

 

[RA_pierce]

Are you saying that the beam of you're 25mW green is equal to or a little brighter than your 300mW Red? That would mean about 2400mW of red or a little bit more would be needed (if my math is right) to match a 200mW green? If so, then matching the beam is totally feasible.

Both the spot and beam seem close to equal with beam diameter of 1.5mm.
To my eyes at least...

I found this:
http://www.cnilaser.com/PDF/RGB_mix_for_laser_show.pdf

 

[jeffd]

Well, thanks for the info. At least I know now, rather than wasting my money futilely.

Its still pretty cool, i wouldnt call it a waste of money for less than $50 you can get yourself a nice <250mw red. And you can have a visible beam in very dark conditions.