Spot size and visibilty - noob question(s)

[Ian]

Hi all,

Just found this great site and this is my first post so please go easy on me :yh:

I have spent ages going through the posts and alsready found tons of info so thanks.

Back to my question(s)

Dot (or is it spot) size:

I realise that there are many different lasers so there will be many different sizes but is there a standard formula i.e if you have a 2mm dot at the laser will it be say 10mm at 10m, 20mm at 20m. 30mm at 30m , etc or are there many variations in the lens setups ? and you have to be specific during purchase or have one custom made

Visibilty:

I am reading here that the green laser seems to be brightest for the power output, but is it possible to have seperate red, green + one other colour
all appear of similar brightness and easily visible in daylight (only dot not beam) out to say 60m.

If this is possible what would be the lowest output available to achieve this (I realise you may need different power outputs to achieve)

Many thanks,

Ian

 

[RA_pierce]

Google "Beam divergence" and "Photopic vision."

 

[Ash]

1. Dot (or is it spot) size:

2. I realise that there are many different lasers so there will be many different sizes but is there a standard formula i.e if you have a 2mm dot at the laser will it be say 10mm at 10m, 20mm at 20m. 30mm at 30m , etc or are there many variations in the lens setups ? and you have to be specific during purchase or have one custom made

Visibilty:

I am reading here that the green laser seems to be brightest for the power output, but is it possible to have seperate red, green + one other colour
all appear of similar brightness and easily visible in daylight (only dot not beam) out to say 60m.

3. If this is possible what would be the lowest output available to achieve this (I realise you may need different power outputs to achieve)

Many thanks,

Ian

1. Dot, Spot, whatever you want. I say "dot" myself.
2. What you are describing is laser "divergence"... with the measurements you gave (ie: 30mm @ 30m) the divergence is around 1.03mRad. Usually laser manufacturers will state the lasers divergence in the product specs. A lower divergence is always better because the laser stays thin for a longer distance and the laser "dot" is as small as it can be at a distance.
Most (non-focusable) lasers are set with very low divergence (<1mRad) by the factory. This is not something that you would have an option of changing, unless you buy (or have made) a laser with focusing ability (which is the most common way for DIY lasers).
3. I'm not sure about the exact ratios, but a 100mW 532nm is about equal to a 300mW 660nm, a 500mW 445nm, and an 800mW 405nm laser.
If you want the lowest output to still be able to see at 60m in daylight, you may be able to get away with 50mW, 150mW, 250mW, and 400mW. :beer:

 

[RA_pierce]

3. I'm not sure about the exact ratios, but a 100mW 532nm is about equal to a 300mW 660nm, a 500mW 445nm, and an 800mW 405nm laser.
If you want the lowest output to still be able to see at 60m in daylight, you may be able to get away with 50mW, 150mW, 250mW, and 400mW. :beer:

Not quite.
The way I see it, 40mW of 532nm is as bright as 300mW of ~655nm. 800mW of 405nm is not even close to as bright as 100mW of 532, maybe more like 30-40mW.
445nm is tricky. The human eye is very sensitive to this wavelength in certain conditions.
200mW of 532 and 300mW of 445 makes a nice balance cyan and appear to be about equal brightness at a short distance, indoors.

Outside in daylight, you can forget about 405nm and 445nm being visible for more than 60 feet. Even 1000mW of 445nm gets washed out over a short distance.

60 meters is a long way to go, especially in daylight. For those conditions nothing less than 200mW of green will work.
Don't forget that the Sun is the brightest thing in our solar system.

Again, the terms you are looking to define are "divergence" and "photopic vision."
Also relevant is "scotopic vision" and "myopia" (when talking about short wavelengths like 445nm and 405nm.

 

[qumefox]

800mW of 405nm isn't going to be visible for more than 30' or so outdoors in daylight.. much less 60m

532nm would be your best option. Probably would need greater than 500mW

 

[Ian]

Wow , thanks for all the great replies so far.

I was wondering wether or not to "stretch" to a 5mW pointer to test but I guess you guys
have blown that one out of the water !

Opinion seems to be varied though between 50mW - 200mW in green

I am in the UK though so bright sunlight is quite rare !

If you viewed the dot through a filter held to your eye would that help make the dot more visible ?