Are Hiking poles needed for light hiking?

Are hiking poles helpful? Yes— especially for balance, stability and shock absorption.
Are they absolutely needed? No.

If you use them at home for light hiking, then they are helpful. Our hotels had them available. You could write and ask your hotel if they provide them.

It really depends on the trails you plan on hiking. Last summer, we rode the gondolas up and hiked moderate trails down in Appenzel. I’m glad I had poles. Same for coming down from the Gornergrat in Zermatt. I did not use them for the Männlichen–Kleine Scheidegg trail but I did when we went down the Cow Trail from Mannlichen to Grindelwald.

I've just come back from a 10-day trip to the Berner Oberland. I'm 69 with average strength and balance for my age. Here's my personal experience:

1. Lauterbrunnen Valley floor trail - Not needed
2. Mannlichen to Kleine Scheidegg Panorama trail - Not needed, but occasionally helpful
3. Grutschalp to Murren - Not needed, but helpful
4. North Face trail, counterclockwise (A section of steep and rough uphill climb) - Very helpful (Needed for those without strong legs and good balance.)
5. Mountain View trail, Allmendhubel to Grutschalp (Sections of steep and rough downhill) - Extremely helpful (Needed for those without strong legs and good balance.)
6. Schynige Platte - Depending on the specific route you take, e.g. going up to the Daube lookout or not (In my case, I went off trail and took a difficult route up) poles are either very useful or needed.
7. Wengen to Staubbachbänkli - Not needed but occasionally helpful.
8. Wengen to Mönchblick - Not needed but occasionally helpful.

In summary:
(1) For truly light hiking such as the Lauterbrunnen Valley walk, I didn't need poles.
(2) For slightly more demanding hikes, e.g. Mannlichen to Kleine Scheidegg, I didn't need poles but would have found them helpful at times.
(3) For mountain trails (these are not light hikes), e.g. North Face, Mountain View, and Schynige Platte, I needed poles for the difficult sections.

I didn't have the right shoes nor any poles at the beginning. I'm glad that one of my shoes broke during my first hike so I bought a good pair for the rest of the trip. I'm especially happy to borrow a pair of poles from my hotel after my first hike, without which I would have fell at least once.