Recently, the blue/violet wavelengths between 400nm and 500nm have been implicated in the development of macular degeneration. BPI® has developed a simple meter that is designed to check the transmittance of lenses for these wavelengths and provide a figure of merit to use in comparing and producing lenses that protect patients from radiations in this wavelength range.

The BPI® UV & Blue Light Analyzer uses LED light sources centered at 400nm, 430nm, 470nm and 505nm to evaluate lens transmission in these regions. The transmission percentage at each range is displayed along with the Wertheim Protection Factor, a figure of merit based on a comparison of the lens’ photopic transmission with its blocking ability for high-energy (blue/violet) wavelengths.

The meter also has caution indicating LEDs which indicate if the lens transmission is higher than that which would be provided by a linear drop in transmission with wavelength from its tV value down to zero in the UVA.

Air (no lens) lights all caution LEDs and has a Wertheim Protection Factor of “0”. A lens with high luminous transmission but minimal high energy blue/violet transmission such as BPI® Total Day has a Wertheim Protection Factor of “43”.

 

BPI® UV/Visible Mini Photometer™
The first portable, hand-held photometer!

• Reads UV or visible light transmission percentage.
• Test lenses in or out of frames.
• Powered by a standard 9 volt battery.
• Battery life is about 40 hours with the display on.
• Easy to use. Calibrate, left button for visible, right button for UV.
• It can be calibrated for either 380 or 400nm UV standards.
• A compensation table for lens power is on the back of the unit.
• The unit automatically shuts down after either button release.
• 5.625" long x 3.25" wide x 3.375" high.
• 14.3 cm long x 8.2 cm wide x 8.6 cm high.
• 8.7 oz (with battery).
• 0.25 kg (with battery).

Set-up kit: Calibration lens. Manual. Patient brochures and stand.

UL listed components. Meets/exceeds CE standards

Set-up kit: Calibration lens. Manual. Patient brochures and stand.

UL listed components. Meets/exceeds CE standards

BPI® Photometers are sold with a calibration lens that is traceable back to the National Institute of Standards and Technology. (NIST). Users should regularly check the performance of their meters with these lenses to ensure continuing accuracy.

Our photometers accurately assess the upper portion of the UVA band between 350 and 400nm. All known lens materials when treated with a UV absorber move the natural cut-off of UV light up to 400nm for commercially available lenses made from CR-39® monomer. No UV light is passed in the lower portions of the UVA or UVB range.

BPI® Photometers can be expected to make an accurate assessment of UV transmission because of the characteristics of UV lenses and UV absorbers. When treated with a UV absorber the natural cut-off point is moved into the region of the UVA that the photometer reads best. In an untreated CR-39™ lens, the error of a photometer could be 10% of the UV transmission reading. (A range of 3 to 4%).

This may seem like a large range of error, however it is insignificant because of the amount of UV that is being passed by the lens. The UV transmission is clearly in the ‘Danger’ zone and the actual percentage of transmission is immaterial.

After the lens has been treated with a UV absorber and the UV transmission reading of the photometer is 1, the same error factor applies. Now however, the error may be 10% of a 1% transmission reading. Again the error is insignificant. The lens is clearly in the ‘Safe’ zone. It can be seen that the accuracy of a BPI® photometer improves as the lens being tested approaches 100% UV blocking.

For customers who require photometers that read to the ANSI standard, BPI® also sells units that read lenses to 380nm and gives a percentage transmission reading based on 315nm to 380nm.