"M'lud, of course my client had good reason to believe that the light emitting device he was using was safe around aircraft, he saw the advert for it on a well known pilots website"....
That is basically what the policy is aiming to avoid.
My crude rule - if I can see the texture of the cloud, then the base is below about 1500ft and I should consider staying on the ground unless I actually want to go IMC, if I can't, it's higher than that and it's *probably* okay to fly.
Crude, but surprisingly reliable.
G