LED-filaments and LED-filament lamps
An LED-filament includes first and second connectors for receiving a variable power; an at least partially light-transmissive substrate; a first LED array of serially connected first LED chips on a front face of the substrate; a second LED array of serially connected second LED chips on the front face of the substrate; a first photoluminescence layer covering the first LED array for generating a first color temperature; a second photoluminescence layer covering the second LED array for generating a second different color temperature; and at least one resistor serially connected to one of the first LED chips, where the first LED array and second LED array are connected in parallel to the first and second connectors, and where current flowing through the first LED and second LED arrays depends on the power applied to the first and second connectors and where the final color temperature of light generated by the LED-filament depends on the power applied to the first and second connectors.
1. An LED-filament comprising:
first and second connectors for receiving a variable power;
an at least partially light-transmissive substrate;
a first LED array of serially connected first LED chips on a front face of the substrate;
a second LED array of serially connected second LED chips on the front face of the substrate;
a first photoluminescence layer covering the first LED array for generating light of a first warmer color temperature;
a second photoluminescence layer covering the second LED array for generating light of a second different and cooler color temperature; and
a linear resistor serially connected to one of the first LED chips,
wherein the first LED array and second LED array are connected in parallel to the first and second connectors,
wherein current flowing through the first LED and second LED arrays depends on the power applied to the first and second connectors and wherein the color temperature of light generated by the LED-filament depends on the power applied to the first and second connectors; and
wherein a current/voltage characteristic (I-V) of the first LED array increases predominantly linearly with voltage and a current/voltage characteristic (I-V) of the second LED array increases generally exponentially with voltage.
2. The LED-filament of claim 1 , wherein a number of LED chips in the first and second LED arrays and the linear resistor are selected such that:
at maximum power applied to the first and second connectors, current flows through the first and second LED arrays and the color temperature of light generated by the LED-filament is a combination of the first and second color temperatures; and
at minimum power applied to the first and second connectors, a majority proportion of current flows through the first LED array and the color temperature of light generated by the LED-filament is predominantly the first color temperature.
3. The LED-filament of claim 2 , wherein, at maximum power, at least 50% of the current flows through the second LED array.
4. The LED-filament of claim 1 , wherein the first array of LED chips comprises fewer LED chips than the second array of LED chips.
5. The LED-filament of claim 1 , wherein the first photoluminescence layer comprises a strip that is in direct contact with and encapsulates each first LED chip of the first LED array, and wherein the second photoluminescence layer comprises a strip that is in direct contact with and encapsulates each second LED chip of the second LED array.
6. The LED-filament of claim 1 , wherein the second photoluminescence layer additionally covers the first photoluminescence layer.
7. The LED-filament of claim 6 , wherein the first photoluminescence layer is in direct contact with each first LED chip of the first LED array, and the second photoluminescence layer is in direct contact with each second LED chip of the second LED array and is also in direct contact with the first photoluminescence layer.
8. The LED-filament of claim 7 , wherein the first photoluminescence layer comprises a strip that is in direct contact and encapsulates each first LED chip of the first LED array and wherein the second photoluminescence layer comprises a strip that is in direct contact and encapsulates each second LED chip of the second LED array and is in direct contact and encapsulates the first photoluminescence layer.
9. The LED-filament of claim 1 , wherein the first photoluminescence layer comprises at least a manganese-activated fluoride narrowband red photoluminescence material selected from the group consisting of: K 2 SiF 6 :Mn 4+ , K 2 GeF 6 :Mn 4+ , and K 2 TiF 6 :Mn 4+ .
10. The LED-filament of claim 9 , wherein the photoluminescence material content of the first photoluminescence layer comprises 70 wt % to 100 wt % of manganese-activated fluoride narrowband red photoluminescence material.
11. The LED-filament of claim 9 , wherein the first photoluminescence layer further comprises at least one selected from the group consisting of: a green to yellow photoluminescence material, and a broadband red photoluminescence material.
12. The LED-filament of claim 1 , wherein the second photoluminescence layer comprises at least one selected from the group consisting of: a green to yellow photoluminescence material, and a broadband red photoluminescence material.
13. The LED-filament of claim 1 , wherein the substrate is elongated in a direction of elongation, and wherein the first and second arrays of LED chips comprise linear arrays that are arranged in parallel in the direction of elongation of the substrate.
14. The LED-filament of claim 1 , wherein the first color temperature is from 1500K to 3500K, and the second color temperature is from 3500K to 7500K.
15. The LED-filament of claim 1 , wherein the first color temperature is from 1800K to 2500K and the second color temperature is from 3000K to 4000K.
16. The LED-filament of claim 1 , wherein the first color temperature is from 1800K to 2500K and the second color temperature is from 2700K to 4000K.
17. The LED-filament of claim 1 , wherein a chromaticity of light generated by the LED-filament depends on the power applied to the first and second connectors.
18. The LED-filament of claim 17 , wherein the chromaticity CIE x,y of light generated by the LED-filament is within three MacAdam ellipses of ANSI standard coordinates on a CIE 1931 chromaticity diagram.
19. The LED-filament of claim 1 , wherein a chromaticity CIE x,y of light of the first and second color temperatures lies above a black body locus on a CIE 1931 chromaticity diagram.
20. The LED-filament of claim 1 , wherein the linear resistor is incorporated in the first LED array.