LED arrangement and LED driving method

A method of controlling an LED arrangement with a light output surface comprising an area of LED chips and an area between the LED chips, comprising:

• during a first portion of a mains input cycle below a first threshold voltage, keeping driving a first current through a first group of LEDs;
• and
• during a second portion of the rectified mains input cycle above the first threshold voltage, keeping driving a second current through a second group of LEDs and through the first group of LEDs, such that the second group of LEDs are turned on for a second duration less than a first duration for turning on the first group of LEDs in each cycle of the rectified mains input,
• wherein a total light output density for the LEDs of the second group per unit area of the light output surface is greater than a total light output density for the LEDs of the first group per unit area of the light output surface and a ratio of an area of LED chips of the second group of LEDs to a second area of the light output surface throughout which the second group of LEDs are distributed, is larger than a ratio of an area of LED chips of the first group of LEDs to a first area of the light output surface throughout which the first group of LEDs are distributed,
• wherein the total light output density for the LEDs of the first group per unit area of the light output surface and the total light output density for the LEDs of the second group per unit area of the light output surface are selected such that a total light output amount for the LEDs of the second group per unit area and per unit time is substantially equal to a total light output amount for the LEDs of the first group per unit area and per unit time.

A LED arrangement comprising:

• a first group of LEDs distributed on the light output surface;
• and
• a second group of LEDs distributed on the light output surface, the first group of LEDS being arranged in series with said second group of LEDs,
• wherein said first group of LEDs is adapted to be powered while the second group of LEDs is adapted to be bypassed in response to a rectified mains input being below a first threshold, and wherein the first group of LEDs and the second group of LEDs are adapted to be powered in response to the rectified mains input being above the first threshold such that the second group of LEDs are adapted to be powered for a shorter duration compared to the first group of LEDs for each cycle of the rectified mains input;
• and
• wherein a total light output density for the second group of LEDs per unit area of the light output surface is greater than a total light output density for the first group of LEDs per unit area of the light output surface, wherein a ratio of an area of LED chips of the second group of LEDs to a second area of the light output surface throughout which the second group of LEDs are distributed, is larger than a ratio of an area of LED chips of the first group of LEDs to a first area of the light output surface throughout which by the first group of LEDs are distributed,
• wherein the total light output density for the LEDs of the first group per unit area of the light output surface and the total light output density for the LEDs of the second group per unit area of the light output surface are selected such that a total light output amount for the LEDs of the second group per unit area and per unit time is substantially equal to a total light output amount for the LEDs of the first group per unit area and per unit time.