By stronger light people mean how many foot candles or lumen plant need, sometimes light intensity also expressed as Lux (there is equation between them).
You can often see they say phals need about 1000-1500 foot candles. Cattleyas if i remember correctly 2000-3000. And vandas more than 3000.
Alsobis your question about natural light or artificial?
For artificial they say it should be on for 10-12 hours, even 14 to imitate summer time.