The BPI® Blue Light Filter 400 Vision Tester is a hand-held, battery-operated blue/violet light source that demonstrates the effectiveness of a blue/violet light blocking lens. Simply place a lens to be tested between the LED lights and your eye, and push the button. The intense violet light beams produced by the source are greatly attenuated by some lenses and the effect is readily observed when the lenses are placed between the source and your eye. You can see for yourself how well each of the three LED's, whose wavelengths peak at 400 nm, is blocked. Compare this with the BPI Blue Light Filter Vision Tester (#109519), whose three LED's peak at 470 nm.

Recently there has been increased interest in protecting the eye from harmful violet and blue light. Anti reflective coatings formulas have been altered to be less effective in this spectral region, reflecting back about 20 percent of the light there rather than allowing its full passage.
BPI® has recognized the need to protect the eye from short wavelength light for many years. Our Blue Barrier / Filter-Vision / Designed Spectrum 450, 500 and 540 absorptive tints were available in the last century. These tints absorb all (not just reflecting back 20%) of the harmful light of wavelengths shorter than 450nm, 500nm and 540nm, respectively, including UV light.
Blue/Violet light in general is a problem for the eye since it scatters more than other wavelengths, causing unwanted light “noise” within the eye. Reducing the spectral range of light entering the eye lens also cuts down on lens chromatic aberration. Age-related macular degeneration problems, which may be exacerbated by blue/violet light, have been mentioned more recently by Dr. Janet Sparrow, et al. in Optom Vis Sci. Jun 2011; 88(6): 759–765.