Brightness control of a status indicator light
An apparatus and method for controlling the brightness and luminance of a light, such as an LED. The embodiment may vary the brightness and luminance of the LED in a variety of ways to achieve a variety of effects. The exemplary embodiment may vary the rate at which the LED's luminance changes, such that an observer perceives the change in the LED's brightness to be smooth and linear as a function of time, regardless of the ambient light level. Changes to the LED's luminance may be time-constrained and/or constrained by a maximum or minimum rate of change.
1. A method for varying a luminance of a light, comprising:
determining a target change in a signal, the signal setting the luminance of the light, the luminance of the light having a minimum luminance level and a maximum luminance level;
determining if the target change is less than a maximum allowed change for the signal;
if the determination that the target change is less than a maximum allowed change is positive, limiting a change in the signal to the target; or
if the determination that the target change is less than a maximum allowed change is negative, limiting the change in the signal to the maximum allowed change for the signal thereby limiting a rate of change in the luminance of the light;
determining a target luminance to be reached by the luminance of the light, wherein the target luminance level is determined at least in part based on a change in ambient light levels;
determining a minimum time to reach the target luminance;
setting a minimum number of timer ticks necessary to vary the luminance from an initial luminance to the target luminance; and
changing the luminance of the light from the initial luminance to the target luminance in a number of timer ticks at least equal to the minimum number of timer ticks.
2. The method of claim 1 , wherein the light is a light-emitting diode.
3. The method of claim 2 , wherein:
the signal is a pulse-width modulation signal having a duty cycle; and
the change in the signal is a change in the signal's duty cycle.
4. The method of claim 1 , wherein the maximum allowed change is user-selectable.
5. A method for varying a luminance of a light, comprising:
determining an initial luminance of the light;
determining a change in ambient light levels using an ambient light sensor;
determining a target luminance to be reached by the luminance of the light, wherein the target luminance level is determined at least in part based on the change in ambient light levels;
determining a minimum time to reach the target luminance;
setting a minimum number of timer ticks to vary the luminance from an initial luminance to the target luminance; and
changing the luminance of the light from the initial luminance to the target luminance in a number of timer ticks at least equal to the minimum number of timer ticks.
6. The method of claim 5 further comprising:
determining if the minimum number of timer ticks is greater than 1; and
if so,
computing a magnitude of a change to achieve the target luminance level;
determine if the magnitude of change is less than two times the minimum number of timer ticks to reach the target level;
if so, then setting a maximum change to one;
if not, then determining a maximum change;
checking if an initial limit is less than the maximum change; and
if so, setting the maximum change to the initial limit;
if not, setting an allowed PWM change per tick to the maximum change.
7. The method of claim 6 , wherein determining a maximum change comprises dividing the change to the target by the minimum number of ticks to target using integer division.
8. The method of claim 6 , wherein the initial limit is an unconstrained value.