Yep, my thought too. You wouldn’t need ten high-power emitters to get an eyeball-safe level of light, even with the diffuser.
The diffuser is crucial. You should never stare directly into a modern LED, even if it’s “only” a 5mm one.
A 1mW laser is enough to do permanent damage to the retina. 10mW of LED light from the tiny chip you get in a 5mm LED is intense enough to be pushing your luck when combined with the focusing effect of the 5mm LED package.
If you experiment with this stuff, please play it safe with your eyes.
Having said all that, it occurs to me that using high power emitters with a diffuser to light up a whole room might be a safer way of getting a similar light exposure without having to look directly into anything.