Re: Perceived Brightness Index
You're correct in that you win the pedant of the day award.
And, of course the math is what dictates what was meant. If it needed clarification, by golly, I think its about as clarified as possible. :thumbsup:
Of course, as an excerpt from a larger thread, there was some context that was now assumed rather than shown.
The order of operands does cover the issue.
The context was in relation to how we judge the "brightness" of a flashlight, which of course is unit-less. I was essentially trying to point out that we don't see lumens, we see the end result of lux on the target.
After that, the same lumens can appear brighter or dimmer, depending upon the surface area its distributed across. The way users view perceived brightness is also influenced by whether, as an individual, they are primarily influenced by the hot spot, or the hot spot and corona, or the hot spot, corona and spill. Different people interpret these values differently when asked how "bright" a light is....and weight them according to their own (Typically subconscious) value system.
An individual's eye chemistry is also responding to different frequencies differently. Some lights put out more of one wavelength than another...so the same lumen output can cause a perceived difference in brightness, someone's eyes respond more, or less, to that emitter's spectrum. IE: You might SEE less even though a light is putting out more lumens, and, it is why two people might perceive a light's brightness differently.
When all of this is considered together, you can consider that a light might be available with two emitter options, and one might have a higher lumen output than the other....and be trying to decide if the added lumen out put will be enough to be worth springing for that option.
The problem with looking at the lumens again comes down to the typically different lens for the different LED. We see fairly consistently that the smaller LED's will throw more (Put the same lumens over a smaller surface area). We see a deeper/wider reflector as also tending to put the same lumens into a smaller patch of light on a target. So, when the light has a different LED, it also tends to have a different reflector, beam shape, etc, as well.
I see over and over again references to a light having to produce twice the lumens to be noticeably brighter. I also see in practice, that there is no such relationship, except by coincidence. In practice, there are too many variables to make that kind of assertion.
For context, I have an ordinary three-way incan GE 50-100-150 watt light bulb for a desk lamp. On the bulb's box, it lists the lumen output at 450-1150-1600 lumens for the three wattages.
I can definetely tell if the light is at the highest or middle settings, and when clicking it to 1600 lumens, it looks brighter than it did at 1150 lumens. That's a ~ 40% increase in lumens being perceived as brighter...not double, a mere 40%. Obviously, that 40% is enough of a difference that its worth having that third/high option on the bulb. LESS than 40% is also observable.
In practice, my 1,600 lumen lights ARE brighter to me than my 1,200 lumen lights, and my 2,000 lumen lights ARE brighter than my 1,600 lumen lights...and so forth. I can SEE MORE with the added light.
Where it would get tricky, is being able to tell what setting that three-way bulb might be at, if I were to walk into the room a day later, not knowing if it were on medium or high...without a reference point/comparison, such as clicking the light to change the brightness. The eye is bad at that: Side by side comparisons are a lot easier. I tried, and found I could do it IF I used a reference point, specifically, something I could see/resolve with the light on high, but not at medium...say a stapler located at the periphery in a shadow, etc.
If I could also see the stapler, it was on high, and so forth. If I didn't find a see/not see test/reference point, it was a lot harder to tell if I was on high or medium.
The conclusion I came to is that you can potentially see more with more light, even if you're bad at judging HOW MUCH more or less light that is.
:wave: