public void setLightSimulationSpeed(float step) {
		if (Math.abs(getTimeStep() - step) < ZERO)
			return;
		float x = (float) getTimeStep() / step;
		setTimeStep(step);
		// NOTE: whether or not the light source is turned on, the interval should be changed in order to avoid
		// the bug that the interval changes abnormally.
		if (lightSource != null)
			setLightSourceInterval((int) (photonGun.getInterval() * x));
	}