LED filament with colored off state masking
An LED filament includes an underlying layer exhibiting a first appearance at a first temperature, and an over-coated layer comprising a thermochromic material that exhibits at the first temperature, a preselected appearance other than the first appearance, and at a second temperature, a transparent or translucent appearance.
1. An LED filament comprising:
an underlying layer encapsulating a series of LED dies of the LED filament exhibiting a first appearance at a first temperature; and
an over-coated layer comprising a thermochromic material that exhibits at the first temperature, a preselected appearance other than the first appearance, and at a second temperature, a transparent or translucent appearance,
wherein the thermochromic material comprises a composite thermochromic pigment loaded in a substrate, the thermochromic pigment comprising a leuco dye, and
wherein the over-coated layer encapsulates the underlying layer such that at the first temperature the color of the LED filament is the preselected appearance as determined by the thermochromic material.
2. The LED filament of claim 1 , wherein the underlying layer comprises a phosphor material.
3. The LED filament of claim 1 , wherein the underlying layer comprises a phosphor material with a doped phosphor and a fluoride host.
4. The LED filament of claim 1 , wherein the underlying layer comprises PFS phosphor (K 2 SiF 6 :Mn 4+ ).
5. The LED filament of claim 1 , wherein the underlying layer comprises a garnet phosphor.
6. The LED filament of claim 1 , wherein the underlying layer comprises an Europium-doped red nitride phosphor.
7. The LED filament of claim 1 , wherein the underlying layer comprises a phosphor material with an absorbing agent.
8. The LED filament of claim 1 , wherein the first appearance includes a yellow, orange, or red color.
9. The LED filament of claim 1 , wherein the first temperature is a non-operating temperature of the LED filament.
10. The LED filament of claim 1 , wherein the composite thermochromic pigment is loaded in a silicone substrate.
11. The LED filament of claim 1 , wherein the leuco dye is microencapsulated with a polymer material.
12. The LED filament of claim 1 , wherein the preselected appearance comprises a preselected color.
13. The LED filament of claim 12 , wherein the preselected color comprises a black, gray, red, yellow, green, blue, or purple color.
14. The LED filament of claim 1 , wherein the preselected appearance comprises a pattern.
15. The LED filament of claim 1 , wherein the second temperature is above the first temperature.
16. The LED filament of claim 1 , wherein the second temperature is an operating temperature of the LED filament.
17. A lighting apparatus comprising the overcoated LED filament of claim 1 .
18. An LED filament comprising:
a layer encapsulating a series of LED dies of the LED filament comprising a mixture of phosphor and thermochromic material that causes the LED filament to exhibit a preselected appearance at a first temperature, and to become transparent or translucent to light at a second temperature,
wherein the thermochromic material comprises a composite thermochromic pigment loaded in a substrate, the thermochromic pigment comprising a leuco dye, and
wherein at the first temperature, the preselected appearance of the LED filament is determined by the thermochromic material.
19. The LED filament of claim 18 , wherein the phosphor material comprises a doped phosphor and a fluoride host.
20. The LED filament of claim 18 , wherein the phosphor material comprises PFS phosphor (K 2 SiF 6 :Mn 4+ ).
21. The LED filament of claim 18 , wherein the phosphor material comprises a garnet phosphor.
22. The LED filament of claim 18 , wherein the phosphor material comprises an Eu + red nitride phosphor.
23. The LED filament of claim 18 , wherein the phosphor material comprises an absorbing agent.
24. The LED filament of claim 18 , wherein the first temperature is a non-operating temperature of the LED filament.
25. The LED filament of claim 18 , wherein the composite thermochromic pigment is loaded in a silicone substrate.
26. The LED filament of claim 18 , wherein the leuco dye is microencapsulated with a polymer material.
27. The LED filament of claim 18 , wherein the preselected appearance comprises a preselected color.
28. The LED filament of claim 27 , wherein the preselected color comprises a black, gray, red, yellow, green, blue, or purple color.
29. The LED filament of claim 18 , wherein the preselected appearance comprises a pattern.
30. The LED filament of claim 18 , wherein the second temperature is above the first temperature.
31. The LED filament of claim 18 , wherein the second temperature is an operating temperature of the LED filament.
32. A lighting apparatus comprising the LED filament of claim 18 .