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FrozenGate by Avery

638nm as dim as a 405?

EpicHam

EpicHam

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Hello there folks.
I just got myself a 638nm 450mW from Survival Laser and I'm just wondering.

When we take a look at the relative brightness chart.
twna.jpg

The beam of a 638nm at around 450mW should be about as bright as a 445nm at around 750mW.

However,in reality that is most certainly not the case.
It appears that a 638nm is MUCH MUCH dimmer . So dim in fact ,the beam is almost on a 5mW 532nm or a 700mW 405 .

I LPMed it so, it is pumping at least 480mW on peak cycles.
However, it just doesn't look the part.


Now here is the question.​

What is causing this?
Is it because of the divergence of 638nm diodes?
Is it because of our scotopic vision spectral sensitivity?
Or is it because of something else entirely?

Would really appreciate some insight into this topic.

:thanks:
 
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The 400-700nm range of visible light is only a guideline, it varies depending on the individual. There are a number of threads about this. I'm saying this based on the fact that you lpm'd it and it was up to snuff. I have a 700mw 638nm and it seems about as bright as my ~1.2W 445nm to me. But if you really want to know, get a second pair of eyes on that beam.
 
bdgreenb said:
The 400-700nm range of visible light is only a guideline, it varies depending on the individual. There are a number of threads about this. I'm saying this based on the fact that you lpm'd it and it was up to snuff. I have a 700mw 638nm and it seems about as bright as my ~1.2W 445nm to me. But if you really want to know, get a second pair of eyes on that beam.
Click to expand...

I did.
Almost 15 pairs of eyes in fact.
My stroll by the beach with my lasers last night started a spontaneous county laser fair.
One of the most common comment I've had on the 638 was.
"Well ,its a bit dim isn't it?"

Do you thing the 4.5mrad divergence has something to do about this or maybe its just out eyes ?
 
Yeah try getting a bunch of people to look at it, each person sees the brightness differently.

Also, the tools used to calculate these brightness comparisons are VERY general/basic, they may not be quite accurate

EDIT: what's the beam diameter and beam divergence of each laser? Beam specs make a difference in brightness too
 
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Beam diameter makes a huge difference in perceived brightness. Send a laser through a BE and it looks dimmer than before the BE.
 
to me, my 1500mW 445 is much brighter than my 1000mW 638. however, my 638's beam has much worse divergence (g2 lens), so it's beam is much wider. they're both really bright. BTW the title says 405, not 445 or 450, so people coming in are thinking violet, not blue-violet
 
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Maybe the diode is being over driven and has shifted towards 650. I have a mits 500 running at 1520 mA and its putting out 1015 mW. It is not excessively bright however and the dot and beam actually look identical in colour to my 650 nm red dual diode. :beer:
 
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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.
 
Well, from the specs sheet ,
DATA%20SHEET%201.jpg

data%20sheet%203.jpg


It appears that a Mitsubishi ML520G71 has a 5.6mm diameter . Not really sure I'm reading it correctly.
As oppose to my 445's spec sheet which didn't state its beam diameter at all. Only at a divergence 0.43mRad.

502885033_621.jpg


That's a pretty big difference.
However, even at range as short as a few meters , the beam intensity difference is still VERY noticeable....

Awkward...
 
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Well from your spec sheet it gives 644 nm @ 400 mA. If you drive it harder (ie have a bad or inefficient diode and must use more current to get the power you want) it could hit 650 nm or more.

Lets say it was at the lower end of the efficiency range from the spec sheet ie 0.8 mW/ mA so if you wanted 450 mW youd have to pump in 562 mA which is way over the recommended current and could easily shift the output wavelength to 650 or higher. :beer:
 
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grainde said:
Well from your spec sheet it gives 644 nm @ 400 mA. If you drive it harder (ie have a bad or inefficient diode and must use more current to get the power you want) it could hit 650 nm or more.

Lets say it was at the lower end of the efficiency range from the spec sheet ie 0.8 mW/ mA so if you wanted 450 mW youd have to pump in 562 mA which is way over the recommended current and could easily shift the output wavelength to 650 or higher. :beer:
Click to expand...

Well, crap.
So you are saying I paid almost $50 extra for a 638nm laser which in the end is just pumping 650nm ??:undecided:
 
grainde said:
Well from your spec sheet it gives 644 nm @ 400 mA. If you drive it harder (ie have a bad or inefficient diode and must use more current to get the power you want) it could hit 650 nm or more.
Click to expand...

I think you are reading the wrong graph.

grainde said:
Probably! My 638 @ 1520 mA is also 650 or higher...;) :beer:
Click to expand...

Have you tested it, or is that a wild guess?
 
I'm no expert here, but I wouldn't think the diode would be driven >15nm away from the advertised spec... I could easily be wrong though
 
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