# How bright must a light bulb to be noticed in a room?

If one has say an 800 lumen bulb, how many lux are necessary in order for a human to detect when it's suddenly turned on in a room with brightness levels of

• 30 Lux
• 50 Lux
• 100 Lux

1.-How many Lux are necessary to catch a human's attention when when looking in the general direction of the bulb?

2.-How many Lux would almost guarantee to catch a human's attention?

Basically, I wish to know the visual detection threshold, but even rough approximates would be helpful. I'm building an attention guidance system and would like to know how bright a light source would have to be in order for a user to detect it (threshold where he might detect it, and where he most likely will).

• From what I've learnt from signal detection studies is that this greatly depends on the reference one uses. For example, going from 0 to 30 may be perceived as a difference but going from 60 lux to 30 may not. – Robin Kramer Sep 11 '17 at 14:11
• @RobinKramer The light bulb would be switched off in each of the aforementioned settings (room at 30, 50 and 100 Lux) and suddenly switched on, so from 0-x dependending on where the user is. What would x have to be for the user to perceive it. – Girauder Sep 11 '17 at 16:06
• As an aside: this will depend on the person (obviously). For a threshold that most people can see, you may want to use/request a lower confidence bound rather than some kind of average. – mflo-ByeSE Sep 11 '17 at 16:06
• @mfloren yeah that's a good point, though both average and a lower confidence bound would be a good starting point right now. – Girauder Sep 11 '17 at 16:08
• Here is a somewhat related question... Consider the answer: contrast is what catches attention. This brings up the point that the lux may change depending on the color of the bulb (and how it contrasts with the base color of the room and pre-existing light) – mflo-ByeSE Sep 11 '17 at 16:11