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# math equasion converting the brightness of green laser to blue

#### ldrago125

##### New member
if a green laser was 50mW, how many mW would a blue one have to be to have the same brightness.

I would guess 50mW green = 75mW blue..

thanks

#### diachi

##### Well-known member
if a green laser was 50mW, how many mW would a blue one have to be to have the same brightness.

I would guess 50mW green = 75mW blue..

thanks

You need to be more specific than just "blue" or "green" too, there are a whole range of wavelengths that can be considered blue and green.

#### hakzaw1

##### Well-known member
You need to be more specific than just "blue" or "green" too, there are a whole range of wavelengths that can be considered blue and green.
Member 'Astrail' has an awesome one in his sig- best I have ever seen. And while you are there dwnld his divergence tool.. again its the best one out there.

As Diachi noted just blue or red wont work at all.

EXAMPLE... one might assume that 660-650 red looks as bright as 635, 638 or 640 BUT you would be wrong-- 1000mW of the best thin beam 640 is as bright to our eyes as 3 or 4000mW of 660 red.
Its a fairly common mistake to buy hi power green only to find you must spend a LOT to get a good white in the end.... best to match the green's power to your existing R &/or B.

100mW of 520 of 532 green laser is a LOT of brightness ...punch in the numbers-- 100mW 520 takes like 5000mW of 405 violet. Also 'white' does not look the same to everyone. Black laser on the other hand is safe and cheap, not requiring eyeware. jk

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#### Cyparagon

##### Well-known member
There are also several distinct ways to measure the colloquial "brightness." Do you want power, luminous flux, luminous energy, illuminance, power density, or luminous efficacy?

#### hakzaw1

##### Well-known member
There are also several distinct ways to measure the colloquial "brightness." Do you want power, luminous flux, luminous energy, illuminance, power density, or luminous efficacy?

^^^ great point!!! :thanks:+rep when sys allows.

#### Encap

##### Well-known member
There are also several distinct ways to measure the colloquial "brightness." Do you want power, luminous flux, luminous energy, illuminance, power density, or luminous efficacy?
Exactly--it helps if you have at least a slight clue concerning what you are talking or asking about :crackup:

idrago125 --- Keep in mind, visual perception are varies. No two people see exactly the same. Color is not a physical property; it is merely the brain’s interpretation of different wavelengths of light. Brightness is a similar situation---not a physical property.

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