Welding Lens Shade Numbers

[MintJulep]

Conceptually I'd like to watch the Venus transit of the Sun on Tuesday.

Practically it seems like the weather will be crappy.

At any rate, various credible-seeming sources on the web suggest a Number 14 shade welding lens as an acceptable filter for staring directly at the sun.

Number 14 shade lenses seem to be difficult to come by.

Are shade numbers additive? That is would an 8 and a 6 together equal 14?

 

[Eltron]

They aren't additive. Amazon sells eclipse viewing goggles and welding goggles that would suffice. Might be too late to get them now, though.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[IRstuff]

Are these numbers supposed to be the equivalent of optical density? If so, they are additive, since they represent the negative logarithm of the absorbance. Since the absorbances are multiplicative, the optical densities are additive.

TTFN
faq731-376

 

[IRstuff]

oops those should have be transmissivities.

TTFN
faq731-376

 

[Ron]

They are additive.