<View
    android:id="@+id/view2"
    android:layout_width="59dp"
    android:layout_height="65dp"
    android:background="@drawable/lightbulb" />

final View normalView = findViewById(R.id.view2);

//Where I need to set the alpha
int alphaValue = /*Some calculation*/
normalView.getBackground().setAlpha(alphaValue);
normalView.invalidate();

class LightbulbView extends View {

    private BitmapDrawable mLightbulbDrawable;
    private Paint mPaint;

    /*All constructors which call through to super*/

    private void initialize(){
        mLightbulbDrawable = new BitmapDrawable(getResources(), BitmapFactory.decodeResource(getResources(), R.drawable.lightbulb));
        mPaint = new Paint();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mLightbulbDrawable.draw(canvas);
    }

    /*Without this, I get an NPE when I do a getBackground on this view*/
    @Override
    public Drawable getBackground() {
        return mLightbulbDrawable;
        //return super.getBackground();
    }
}

<ImageView
    android:layout_width="wrap_content"
    android:id="@+id/imageView1"
    android:layout_height="wrap_content"
    android:src="@drawable/lightbulb"
></ImageView>

final ImageView imageView = (ImageView) findViewById(R.id.imageView1);
imageView.setAlpha(alphaValue);

<FrameLayout
        android:id="@+id/frameLayout1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
    >
        <ImageView
            android:layout_height="wrap_content"
            android:src="@drawable/lightbulb_content"
            android:layout_width="wrap_content"
            android:id="@+id/bulbContent"
        ></ImageView>
        <ImageView
            android:layout_height="wrap_content"
            android:src="@drawable/lightbulb"
            android:layout_width="wrap_content"
            android:id="@+id/bulb"
        ></ImageView>

    </FrameLayout>

final ImageView bulbContent = (ImageView) findViewById(R.id.bulbContent);
//Where I need to set the alpha
int alphaValue = /*Some calculation*/
normalView.getBackground().setAlpha(alphaValue);
bulbContent.setAlpha(alphaValue);