Randomized Lighting with Python

This code looks good! But I still have some notes to clean it up a bit.

First, all your constants (start_delay_range, brightness_range, and duration_range) should really be part of the Light class since they're used specifically in there. If that's where they're relevant, keep them there. Plus this makes it easier to do from light_tools import Light and not be caught without necessary values.

class Light():
    '''
    Define a light object.

    Attributes:
        name (str): Name of the light.
        device_id (int): The Indigo ID of the device.
        dimmable (bool): Set the light as dimmable or not.
    '''

    # (min/max) seconds to delay before light turns on (randomized every time)
    START_DELAY_RANGE = (15, 70)
    # (min/max) brightness (0-100, randomized every time)
    BRIGHTNESS_RANGE = (50, 85)
    # (min/max) duration for light to stay on (randomized every time)
    DURATION_RANGE = (300, 900)

Next, you might want to use the @property decorator for your functions. Decorators are really interesting to look into, but in this case @property is a simple builtin that means you can use the function like an attribute of your class that's evaluated each time. Simply put, you don't need to call it any more.

@property
def start_delay(self):
    '''Return random delay within <start_delay_range>.'''
    return random.randint(start_delay_range[0], start_delay_range[1])

def run(self):
    '''Turn on the light to <brightness> after <start_delay> for <duration>.'''
    if self.dimmable:
        # Turn on light
        indigo.dimmer.setBrightness(self.device_id,
                                    value = self.brightness,
                                    delay = self.start_delay)

Notice that it's now just self.brightness? It's still evaluating brightness each time you call it, but the syntax looks better. It's more like an attribute than a function call that could do who knows what (even though semantically you could still do anything in the function, you're signalling that this is a simple attribute being returned).

One minor point is that I would move the lights list into the if __name__ == '__main__' block. It will still be available in the global namespace, but it wont run any more unless the script is actually run. So again, if someone wants to import Light they wont get this strange recurring slowdown with every import.

My last point is debatable, but personally I would add an optional parameter to Light to immedidately start running.

def __init__(self, name, device_id, dimmable, start=False):
    self.name = name
    self.device_id = device_id
    self.dimmable = dimmable
    if start:
        self.run()

Now instead of having to always call light.run() after instantiation, you have the option to just pass start=True and have it run as soon as it's created. Generally I don't like having boilerplate set up at the start of a class. If it needs some code to properly be set up, that's a prime candidate for __init__.