Warm dimming LED-filaments and LED-filament lamps
An embodiment of an LED lamp that generates light of a color temperature that decreases with decreasing power applied to the LED lamp may include at least one lighting arrangement that may include a first LED array of serially connected first LED chips, a second LED array of serially connected second LED chips; a first photoluminescence layer covering the first LED array for generating light of a first color temperature; a second photoluminescence layer covering the second LED array for generating light of a second different color temperature; and a linear resistor serially connected to the first LED array, wherein the first LED array and second LED array are connected in parallel.
1. An LED lamp for generating light of a color temperature that decreases with decreasing power applied to the LED lamp, the LED lamp comprising:
a first LED string of serially connected first LED chips,
a second LED string of serially connected second LED chips,
a first photoluminescence arrangement for covering the first LED string for generating light of a first color temperature,
a second photoluminescence arrangement for covering the second LED string for generating light of a second different color temperature, and
a linear resistor serially connected with the first LED string;
wherein the first LED string and second LED string are connected in parallel; and
wherein a current/voltage characteristic (I-V) of the first LED string increases substantially linearly with increasing voltage and a current/voltage characteristic (I-V) of the second LED string increases generally exponentially with increasing voltage.
2. The LED lamp of claim 1 , wherein a proportion of current flowing through the first LED string compared with a proportion of current flowing through the second LED string depends on the power applied to the LED lamp.
3. The LED lamp of claim 1 , wherein at a maximum operating power, current passes through both the first and second LED strings and a color temperature of light generated by the LED lamp is between the first and second color temperatures; and
wherein at a minimum operating power, a majority of current flows through the first LED string and a color temperature of light generated by the LED lamp is substantially the first color temperature.
4. The LED lamp of claim 3 , wherein at the maximum operating power, at least 50% of the current flows through the second LED string.
5. The LED lamp of claim 1 , wherein the first LED string comprises fewer LED chips than the second LED string.
6. The LED lamp of claim 1 , wherein the second photoluminescence arrangement additionally covers the first photoluminescence arrangement.
7. The LED lamp of claim 1 , wherein the first photoluminescence arrangement comprises a narrowband red phosphor 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+ .
8. The LED lamp of claim 1 , wherein the first color temperature is from 1800K to 2500K, and the second color temperature is from 3000K to 4000K.
9. The LED lamp of claim 1 , comprising a connector base.
10. The LED lamp of claim 1 , comprising a light transmissive envelope.
11. The LED lamp of claim 1 , comprising an at least partially light transmissive substrate on which the first LED string and the second LED string are mounted.
12. The LED lamp of claim 1 , wherein the linear resistor is in the first LED string.