Optical light diffuser and method for measurement thereof
The invention relates to optical light diffusers for use with point light sources, such as LED lighting. The optical diffusers achieve an optimum balance of light transmission and hiding power. The optical light diffuser is a transparent plastic matrix, such as Plexiglas® resin from Arkema Inc., having organic particles dispersed within the matrix. The particles are crosslinked beads having specific particle sizes and loading. Different beads can be combined to provide added properties such as a textured surface, and to optimize hiding power and light transmission. The invention also relates to a luminous device containing at least one light-emitting diode and a cover made of the optical light diffuser. The invention further relates to a method for assessing hiding power.
1. A cover for a point light source having a composition comprising a transparent thermoplastic or thermoset plastic matrix having dispersed therein a blend of from 1 to 10 equivalent loading weight percent of small cross-linked diffusing particles having a mean particle size of from 2 to 20 microns, and from 2 to 10 equivalent loading percent by weight of large cross-linked diffusing particles having a mean particle size of from 40 to 80 microns, the weight percent based on the polymer matrix, and wherein the optical transmission is greater than 75 percent and the hiding power is greater than 40 percent, and wherein said cover has a surface roughness of from 0.5 to 4 microns.
2. The cover of claim 1 , comprising from 6 to 10 weight percent of said small cross-linked diffusing particles and wherein said optical transmission is greater than 85% and said hiding power is greater than 85%.
3. The cover of claim 1 , wherein said cover has a surface roughness of from 1 to 3 microns.
4. The cover of claim 1 wherein the diffusing cross-linked particles are a blend of 2 to 6 weight percent of said small cross-linked diffusing particles, and from 4 to 6 weight percent of large cross-linked diffusing particles.
5. The cover of claim 1 , wherein said transparent polymer comprises a polymethyl methacrylate (PMMA) homopolymer or copolymer.
6. The cover of claim 1 , wherein said cross-linked diffusing particles have a narrow particle size distribution, wherein 90 percent by weight of the particles are within 50% of the mean particle size.
7. The cover of claim 1 , wherein the refractive index difference between the transparent polymer matrix and said cross-linked diffusing particles is between 0.015 and 1.
8. The cover of claim 1 , wherein said transparent polymer matrix further comprises one or more additives selected from the group consisting of impact modifiers, and other additives typically present in polymer formulations, including but not limited to, stabilizers, plasticizers, tillers, coloring agents, pigments, dyes, antioxidants, antistatic agents, surfactants, toner, refractive index matching additives, additives with specific light diffraction, light absorbing, or light reflection characteristics, and dispersing aids.
9. The cover of claim 1 , wherein said cross-linked particles are essentially spherical.
10. The cover of claim 1 , wherein said cross-linked particles are irregular in shape.
11. A luminous device comprising at least one point light source, and said cover of claim 1 .
12. The cover of claim 2 , wherein said small cross-linked diffusing particles have a mean average of from 3 to 15 microns.
13. The cover of claim 1 , wherein said transparent polymer is an alloy of PMMA with polylactic acid and/or polyvinylidene fluoride.
14. The luminous device of claim 9 , wherein the point light source comprises one or more LEDs.