LEDs

Question 1

Haitz law

Answer 1

LEDs have increased in brightness by a factor of 20 every ten years since they were introduced (in 2000)

Question 2

Pulse-width modulation power supply

Answer 2

power supply converts AC to low voltage DC.
within fixed window of time, it switches the current on for a percentage of the window and off for the remaining duration. resulting current is a square wave-form with variable duty cycle.
the wider the width of the pulse, the dimmer the output. At ful brightness, current is steady DC and at blackout, no current
Frequency of modulation typically 300 Hz or higher, low frequencies can interact with frame rate of video and film, flicker, especially at lower duty cycles or dimming levels.

Question 3

phase-control dimming

Answer 3

use electronic switch controlled by DMX
DMX control signal sets the dimming level, the dimmer then turns the applied voltage off and on once in each half cycle of the voltage sine wave (120 times every second in a 60 Hz system or 100 times every second ina 50 Hz system)
by varying the legnth of the time the voltage is held on compared to the length of time it is held off determines the dimming level

Question 4

triac

Answer 4

solid-state switch controlled by a low-voltage control signal
bi-directional switch, can conduct current in both the positive and negative directions

Question 5

silicon controlled rectifier

Answer 5

solid-state switches controlled by low-voltage control signal
a uni-directional switch, can conduct in only one direction.
dimmers that have SCRs have two of them connected in inver-se parallel, alllows one SCR to cool off while the other is conducting