It depends… What kind of devices are they? Some people run hundreds, but a large number of them will be mains-powered routers. You mention some bulbs, so they’re probably routers. Battery powered sensors are parasites - they consume network resources and contribute nothing.
If you’re using ZHA you can check channel usage by going to the ZHA card in Devices & Services, clicking on the three dots next to Configure and selecting Download diagnostics. Right at the end of the file you get will be something like this:
"energy_scan": {
"11": 73.50699819621309,
"12": 3.2311094587038967,
"13": 70.89933442360993,
"14": 91.05606689948522,
"15": 85.82097888710312,
"16": 65.26028270288712,
"17": 7.659755505061292,
"18": 43.057636198227904,
"19": 1.1664179210724432,
"20": 62.257682586134884,
"21": 2.509919386096536,
"22": 3.6632469452765037,
"23": 4.15070068297423,
"24": 0.9017765778954641,
"25": 1.5075412082833717,
"26": 21.09014924761344
The percentages show the amount of noise on each channel, including Zigbee traffic, wi-fi traffic (your neighbour’s as well as yours) and general interference.
Lots of advice in the Community guides:
- Zigbee networks: how to avoid interference and get the best range and coverage
- Migrating from a Philips Hue bridge to SkyConnect
- A to Zig - a Zigbee glossary
- Not many people know that - a random collection of Zigbee trivia
- How to set up custom device handler quirks in ZHA
- Zigbee buyer’s guide
- Is Zigbee right for you?