HSDP2110S, HSDP2111S, HSDP2112S, HSDP2113S, HSDP2114S, HSDP2115S

2006-01-23

15

Optical Considerations

The .200" high character of the HDSP211XS gives readability up to eight feet. Proper filter selection enhances readability over this dis-

tance.

Using filters emphasizes the contrast ratio between a lit LED and the character background. This will increase the discrimination of differ-

ent characters. The only limitation is cost. Take into consideration the ambient lighting environment for the best cost/benefit ratio for filters.

Incandescent (with almost no green) or fluorescent (with almost no red) lights do not have the flat spectral response of sunlight. Plastic

band-pass filters are an inexpensive and effective way to strengthen contrast ratios. The HDSP2110/2112S are red/high efficiency red dis-

plays and should be matched with long wavelength pass filter in the 570 nm to 590 nm range. The HDSP2113S should be matched with a

yellow-green band-pass filter that peaks at 565 nm. For displays of multiple colors, neutral density grey filters offer the best compromise.

Additional contrast enhancement is gained by shading the displays. Plastic band-pass filters with built-in louvers offer the next step up in

contrast improvement. Plastic filters can be improved further with anti-reflective coatings to reduce glare. The trade-off is fuzzy characters.

Mounting the filters close to the display reduces this effect. Take care not to overheat the plastic filter by allowing for proper air flow.

Optimal filter enhancements are gained by using circular polarized, anti-reflective, band-pass filters. The circular polarizing further

enhances contrast by reducing the light that travels through the filter and reflects back off the display to less than 1%.

Several filter manufacturers supply quality filter materials. Some of them are: Panelgraphic Corporation, W. Caldwell, NJ; SGL Homalite,

Wilmington, DE; 3M Company, Visual Products Division, St. Paul, MN; Polaroid Corporation, Polarizer Division, Cambridge, MA; Marks

Polarized Corporation, Deer Park, NY, Hoya Optics, Inc., Fremont, CA.

One last note on mounting filters: recessing displays and bezel assemblies is an inexpensive way to provide a shading effect in overhead

lighting situations. Several bezel manufacturers are: R.M.F. Products, Baklava, IL; Nobody Components, Griffith Plastic Corp., Burningly,

CA; Photo Chemical Products of California, Santa Monica, CA; I.E.E.-Atlas, Van Nuys, CA.