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# NEW TOOL: Calculate Relative Brightness (of Wavelengths in nm)

##### Well-known member
LPF Site Supporter
This post is adding to the subject, the link recently quit working, can you fix it or know where another one is? I thought this information so useful, I added it to my signature but didn't realize it was yours until I found this googling for another one.

Thanks.

#### rhd

##### New member
This post is adding to the subject, the link recently quit working, can you fix it or know where another one is? I thought this information so useful, I added it to my signature but didn't realize it was yours until I found this googling for another one.

Thanks.
Can you point me to a free ASP hosting provider? Jabry seems to have quit working.

##### Well-known member
LPF Site Supporter
I will need to google what ASP means, sorry. If I figure it out and find something, I will be sure to do that.

#### Teej

##### New member
I'm just pointing out that there a lot of questions are about how many lumens are brighter, etc..and, you can't SEE lumens...its the wrong unit.

Essentially, lumens are what are sent out...but the intensity of the dot is a function of the light that bounces back to your eyes.

THAT is measured as lux typically.

As the human eye is a LOUSY light meter, we're terrible at judging how bright a dot of light is.

There are devices that can measure lux (lux meters), but you'd need to get one that will read a laser accurately.

The other issue to consider is that lux is lumens per square meter.

So if you know the lumens, the cd, and the size of the dot, you can calculate the lux...but you won't.

The useful part revolves more around the idea that if you have the same sized dot, and, get it with more lumens in the same surface area....doubling the lumens doubles the lux...its a one to one ratio if the dot size is constant.

When you add in what nm, you run into yet another issue...Lumens (And therefore lux) are weighted by the eye's response to various nm ranges...so some wavelengths "count more or less than others".

So, if you use a lightly weighted wavelength, a measured lux would be low, etc.

As discussed, when completely night adapted for example, you are essentially seeing in black and white anyway. The less adapted you are, the more color you might be able to distinguish.

Its all a question of degree after that.

Some people will see red better than others for example, and, that will impact their perception of that nm range, and so forth.

#### rhd

##### New member
I'm just pointing out that there a lot of questions are about how many lumens are brighter, etc..and, you can't SEE lumens...its the wrong unit.

Essentially, lumens are what are sent out...but the intensity of the dot is a function of the light that bounces back to your eyes.

THAT is measured as lux typically.

As the human eye is a LOUSY light meter, we're terrible at judging how bright a dot of light is.

There are devices that can measure lux (lux meters), but you'd need to get one that will read a laser accurately.

The other issue to consider is that lux is lumens per square meter.

So if you know the lumens, the cd, and the size of the dot, you can calculate the lux...but you won't.

The useful part revolves more around the idea that if you have the same sized dot, and, get it with more lumens in the same surface area....doubling the lumens doubles the lux...its a one to one ratio if the dot size is constant.

When you add in what nm, you run into yet another issue...Lumens (And therefore lux) are weighted by the eye's response to various nm ranges...so some wavelengths "count more or less than others".

So, if you use a lightly weighted wavelength, a measured lux would be low, etc.

As discussed, when completely night adapted for example, you are essentially seeing in black and white anyway. The less adapted you are, the more color you might be able to distinguish.

Its all a question of degree after that.

Some people will see red better than others for example, and, that will impact their perception of that nm range, and so forth.
I don't think I've ever spoken about lumens.

In terms of this whole light vs dark adapted, if you see a bright colored laser light when your eyes are dark adapted, you're not suddenly seeing that beam in black and white. People keep bringing up variations on that theme, and people keep pointing out that it's nonsense.

Anyway, it is what it is. This tool is basically ONLY a tool for easily applying relative sensitivity curves, with optional Raleigh scattering. Nothing more. Leave it at that. The headache of this never ending debate about accuracy is why I initially took the tool down. I don't know why it's down now. I'll try to find a free ASP host to put it back online. If anyone has suggestions, let me know.

#### Teej

##### New member
The lumen is a weighted scale to the response of the human eye, and that's what those charts are aligned to. Other posts, such as "is 2 lumens twice as bright as 1 lumen", (Not by you) etc, referred more directly.

So, its an incredibly complicated process.

The primary thrust was simply to point out that lux is the normal unit used to describe the intensity of a viewed dot of light...and that as lux is based upon lumens per square meter, and, lumens are already a weighted unit relative to the eye's response, that makes lux include the intensity relative to the eye's response to that wavelength.

If you are looking for how to express the intensity of a dot of light by wavelength, lux would therefore be a logical candidate, as that's its primary job.

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#### Atomicrox

##### Well-known member
The link is working for me but it gives an error when I click on Calculate:

Code:
``````Microsoft JET Database Engine error '80004005'

Unspecified error

/lsrtools/RelativeBrightness/index.asp, line 342``````
Looks like it's just a database error, might not be hard to fix without going to another host.

#### clansley

##### Active member
Hi rhd - are you open to the idea of giving the source to me - I'll see if can get it running on some small device I have (I presume the traffic isn't huge). Whilst it isn't perfect it is the best we have until somebody does something better.

#### rhd

##### New member
Hi rhd - are you open to the idea of giving the source to me - I'll see if can get it running on some small device I have (I presume the traffic isn't huge). Whilst it isn't perfect it is the best we have until somebody does something better.
If someone can just find a free hosting provider that runs on Windows and allows ms access dbs, I'm just reupload it. I just haven't had time to go looking.

Found these:

Hope they help,
Chris.

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rhd

#### Phased Array

##### New member
I could use this program right now!
I just tore down a Laser Genetics ND3 laser flashlight with a 18mw 532nm green laser, and swapped it out to more 'pleasing to the wildlife' 170mw 638nm red laser. There seems to be no perceived increase in illumination @ 10X the power. How much more power do I need to get an increased illumination level based on my human vision? Relative to the green.
The green laser (flash)light gives a lot more useful illumination because humans are more sensitive to it, thats why Laser Genetics uses it.

#### Phased Array

##### New member
:gj:
Thx, That helps a lot!

#### beamjunkie7

##### Member
Sorry to resurrect old threads, but the tool has stopped working -- please let me know if there is anything I can do to help get it back up! It was very useful to me, and I miss having it already. Is it the ASP hosting again? Or is it just me that is having this issue?

If it is ASP or hosting that is causing the problem, this tool seems pretty solid:
http://ultidev.com/products/UWS-Cassini-Pro/Default.aspx

#### Anthony P

##### Active member
LPF Site Supporter
Sorry to resurrect old threads, but the tool has stopped working -- please let me know if there is anything I can do to help get it back up! It was very useful to me, and I miss having it already. Is it the ASP hosting again? Or is it just me that is having this issue?

If it is ASP or hosting that is causing the problem, this tool seems pretty solid:
http://ultidev.com/products/UWS-Cassini-Pro/Default.aspx
The link from the original post still works.http://lsrtools.1apps.com/relativebrightness

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