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638nm as dim as a 405?

grainde

grainde

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Cyparagon said:
I think you are reading the wrong graph.
Click to expand...

No I took the info from the table.

Peak wavelength Max - 644 nm

This was measured at 220 mW according to the data. So going from their (table) max min mW/mA this could be between 170 - 270 mA.

So if at 270 mA the max poss wavelength is 644 nm, why should it be hard to believe that at twice the max recommended current and more, the wavelength wont shift a further 6 nm?

Cyparagon said:
Have you tested it, or is that a wild guess?
Click to expand...

I dont have a spectrometer. Qualitatively not quantitatively, my 1 W 638 looks similar to, if not a slightly deeper red hue than, my 650 dual and its not much brighter visually.

On my LPM the dual gives exactly 250 mW and the 638 gives 1025 mW. :beer:


Edit: the ML501P73 gives a max wavelength of 644 nm at 500 mW. So thats given between 400 - 700 mA (mW/mA from spec sheet below).

http://www.mitsubishielectric.com/s.../laserdevice/ldindis/638nm/ml501p73_p1245.pdf

So same situation here too.
 
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EpicHam

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grainde said:
No I took the info from the table.

Peak wavelength Max - 644 nm
Current Max - 400 mA

These were measured at 220 mW according to the data. So going from their (table) max min mW/mA this could be between 170 - 270 mA.

So if at 270 mA the max poss wavelength is 644 nm, why should it be hard to believe that at twice the max recommended current and more, the wavelength wont shift a further 6 nm?



I dont have a spectrometer. Qualitatively not quantitatively, my 1 W 638 looks similar to, if not a slightly deeper red hue than, my 650 dual and its not much brighter visually.

On my LPM the dual gives exactly 250 mW and the 638 gives 1025 mW. :beer:


Edit: the ML501P73 gives a max wavelength of 644 nm at 500 mW. So thats given between 400 - 700 mA (mW/mA from spec sheet below).

http://www.mitsubishielectric.com/s.../laserdevice/ldindis/638nm/ml501p73_p1245.pdf

So same situation here too.
Click to expand...

So does that mean that we are better off buying 660nm lasers at higher power than high powered 638nm for the reason that .

1: 660nm lasers have a circular beam profile
2: Lower divergence at 1.5mRad as compared to almost 4.5mRad
3: Lower chance of "red shifting
4: The price difference between a 638nm diode and a 660nm doesn't justify the visibility and color difference

Am I correct?
 
grainde

grainde

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EpicHam said:
So does that mean that we are better off buying 660nm lasers at higher power than high powered 638nm for the reason that .

1: 660nm lasers have a circular beam profile
2: Lower divergence at 1.5mRad as compared to almost 4.5mRad
3: Lower chance of "red shifting
4: The price difference between a 638nm diode and a 660nm doesn't justify the visibility and color difference

Am I correct?
Click to expand...

1 and 2 yes. 3 and 4 not really.

If you over drive the 650's Im sure they will shift too, Im just not sure by how much.

There arent many 1 W red diodes and most 650's are around 250 - 300 mW excluding C-mounts, which are expensive anyway. If you keep the 638 at a low temp and drive it at its recommended current then you will still have more power than most 650's and the beam will be much more visible. Depends what you want; WOW factor, bragging rights and/or burning ability. However, the latter is probably mute these days with the 445's. :beer:
 
Cyparagon

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grainde said:
So if at 270 mA the max poss wavelength is 644 nm, why should it be hard to believe that at twice the max recommended current and more, the wavelength wont shift a further 6 nm?
Click to expand...

You said it yourself. It is the maximum possible wavelength. It is not a typical value.

Look at the bottom graphs here instead for a better estimate of wavelength.

data%20sheet%203.jpg
 
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grainde

grainde

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Cyparagon said:
You said it yourself. It is the maximum possible wavelength. It is not a typical value.
Click to expand...

Yeah max poss at 220 mW or 270 mA. Thats what they measured the max value at. We'd have to get values at higher powers to confirm it is the absolute max and no longer dependent on input current. Having said that, the graph current vs wavelength does seem rather flat... I give you that.

The other one for T vs wavelength isnt though. Maybe there is localised heating of the dye and heat cant be removed quickly enough through the emitter surface/diode base interface and thats why they recommend a much lower current?

We all know the efficiency drops to the point of diminishing returns when pushing these diodes. This is probably due to heat and if so, could explain why at much higher currents we see such a large shift in the wavelength.:thinking: :beer:

Edit: Ill cool my 1 W 635 tonight, measure the output and have a look to see if its blue shifted wrt my 650.
 
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grainde

grainde

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Cyparagon said:
You have a really hard time admitting when you're wrong, don't you?
Click to expand...

:thinking: I didnt realise it was some sort of competition...I thought we were trying to find out why it shifts so far?

Either way I dont see how Im wrong? Ive compared 650 to my over driven 638 and the colour is, for all intents and purposes, the same. I dont have one here, but I have seen a 635 and it was very orange in comparison. Anyway I was trying to find answers...You quoted some figures from a spec sheet under very specific conditions and without a full data set. What you want to extrapolate is your business. ;)
 
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EpicHam

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norbyx said:
I think that those programs that compare the brightness of one color to another are mostly wrong in their calculations.
As for every individual sees light and colors in a different way.
A good way to check your laser is to take a picture of both lasers side by side with a digital camera. Cameras don´t lie so you will see if the brightness in the picture is actually what you are seeing or not.
When I do this type of tests I realize that most times my 1W red lasers are much more bright that what I can actually see. Sometimes they have a highly dominant color red in the picture.

Try it it might help.
Click to expand...

I did , but cameras lies about the laser's beam brightness.
In the end, the photos should reflect what people will see under the circumstances when the photo was taken.
You can go click a few of the reviews I've taken , and the beamshots I've taken is WAAAY brighter on camera then perceived.

grainde said:
:thinking: I didnt realise it was some sort of competition...I thought we were trying to find out why it shifts so far?

Either way I dont see how Im wrong? Ive compared 650 to my over driven 638 and the colour is, for all intents and purposes, the same. I dont have one here, but I have seen a 635 and it was very orange in comparison. Anyway I was trying to find answers...You quoted some figures from a spec sheet under very specific conditions and without a full data set. What you want to extrapolate is your business. ;)
Click to expand...
39795876.jpg


I do have a question tho.
How did you come with the conclusion that the 638 diode would be pumping 650nm at 450mW?
Cos when I look at the graph , the nm to current driven-power relationship is pretty flat at 25C.
Shouldn't it be more in the line of 640nm under typical operation as stated on the datasheet?
 
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Cyparagon

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grainde said:
I thought we were trying to find out why it shifts so far?
Click to expand...

You're claiming a 638 diode will be 650nm+ in practice. You have no evidence for this besides "my two red lasers look the same color to me." Surely you must realize how absurd this is. Eyeballs are not any better at measuring wavelength than they are at measuring power. Your "650" is actually 660nm or higher, anyway. And that number is from a spectrometer, not from your ass.
 
hwang21

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Alright let's try to avoid flaming here... just keep calm and explain slowly, surely there's some kind of misunderstanding somewhere...
 
Leodahsan

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Actually, cyp has a spectrometer. He can test himself ;)

The values indicates what a manufacturer guarantees of a product. Typ indicates that most of tested samples are on that value, where max. is the maximum the sample will go.

If you look the typical characteristics closely, you will see
~636nm @ 220mW and 220mW @ 330mA. TYPICAL. You can get 632nm there, or 644. No more, No less.

Stop fighting.
 
EpicHam

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Leodahsan said:
Actually, cyp has a spectrometer. He can test himself ;)

The values indicates what a manufacturer guarantees of a product. Typ indicates that most of tested samples are on that value, where max. is the maximum the sample will go.

If you look the typical characteristics closely, you will see
~636nm @ 220mW and 220mW @ 330mA. TYPICAL. You can get 632nm there, or 644. No more, No less.

Stop fighting.
Click to expand...

If you think this is still a fight about saying who's right and who's wrong .
You are judging things FAAARRRR too simply.
 
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