A few rules of thumb to go by:
1. Safe working height is 4' higher than the top ladder height.
2. Maintain 3 points of contact at all times. Preferably both feet+1 hand, but leaning into it with the upper body does work. Not as good, but it happens.
This means having a ladder tall enough for your upper body to have good contact points.
3. 12' ladders are the max length normally sold as a step-ladder, and they're not cheap. Extension ladders, if used, normally need a 1:4 leaning ratio.
4. Carrying things up/down means your points of contact, and your balance, may be compromised. Had a coworker die from falling off the BOTTOM step (9" from the ground) because she had her hands full. Even if only one hand is used, it limits your ability to grasp the ladder if needed. It's
instinctive to NOT drop whatever we are carrying, which keeps people from grabbing the ladder when their balance changes. Use a rope & basket.
5. Would rolling scaffolding be easier/quicker? It can be rented by the day or the week. Many ladders can be rented as well.
6. Replace all the lights at the same time, whether working or not. That limits your time spent in the future on the same issue.
7. Buy the best lights you can find, so this issue is reduced or removed in the future.