I just got a pair of glasses to use for computer use (astigmatism correction plus add for reading distance). I decided to give the blue blocker option a try. They included a blue laser pointer as a promotion.
When I point the laser pointer through the lenses you can’t see it on a surface. That is supposed to prove the efficacy of the lens. However, if I put the glasses on, I can still see the dot on whatever I point the laser at. (I have not tried pointing the laser at my eyes for obvious reasons.)
Why do the lenses filter direct blue light from a light source, but they don’t filter reflected blue light from the same source?
If the glasses filter blue light, why don’t they have a yellow tint?
Interesting question. It would be easier if I knew what the spectral transmission of the lenses were. It could be that the blue blocking is so narrow that it mainly affects the laser line and allows other blue through. In that case, you’re not completely elimination the blue and color would look more normal.
Yellow is the complementary color of blue. Most blue laser pointers are around 405 or 450 nm, and if you go through the white point of a CIE diagram it takes you pretty close to yellow, so you’re right there.
as for why you completely block the laser pointer if you pass it through the glasses onto a white surface, but you don’t block it when you put the glasses on and look at the spot on a white surface, I cannot say. I would thin that sending the laser directly through the glasses would be a more severe test. If the laser actually had some admixture of another line that was not blocked so well by the glasses, I would expect this to produce a visible spot under either set of circumstances.
Could what you see when pointing the laser at a surface be light reflected at a frequency just far enough off blue that it can be seen? Is that possible?
Back when I flew RC sailplanes I spent hours looking up into a blue sky. I found a set of glasses that were tinted with Diamond Dye 550. They pretty much blocked anything remotely blue. Blue cars looked grey etc. Never had a blue laser to try out back then.
They’re reading glasses. When you point the laser through them, the beam is diffused/spread out. When you look through them at the spot, the spot is focused / sharpened.
They also block blue light, but not entirely.
Reflection doesn’t change frequency, but florescence does. White paper may contain fluorescers, to make it more white, they may well be energised by blue light, and if so, the frequency will be different.
Just what I was coming back to suggest. The color might be shifted slightly by the fluorescence, but maybe not enough to notice. Especially through a colored filter