Monochromatic Light and the Human Eye...

First, I am an idiot. None of this came from my brain. I picked Henry's brain which is much better than picking his nose.

Folks asked before what lumen output is on the HDS monochromic lights (Dark Adaption Red, Hunter Green, Forensic Blue, UV, and Amber). Since these are not measured in lumen output but in mW.

First point to remember here is that the exact same amount of power is going into the emitter with all the HDS monochromic lights. This doesn't change (this is important later in order to confuse you).

So let's muddy things.
If the Dark Adaption Red is 900mW and the Amber is 250mW outputs, then we can assume that the red is brighter, right? Wrong.

This has to do with how your eyes are color sensitive. Here is a chart of how sensitive your eyes are to different colors...



As you can see, your eyes are most sensitive to green (555 nanometers). This means red light needs to be "brighter" or have more mW to appear as bright as green. Same with the other monochromic colors. It may not be easy being green, but you will be seen better.

So, you should be asking yourself "if an emitter is lower in mW output, shouldn't that run longer since the amount of juice being fed to said emitter is the same?".

Nope.

The reason for this is that different materials are used in the emitter in order to get it to generate those specific monochromatic colors. The efficiency of these materials for each color is different.

Power (being constant) x efficiency of the emitter converting electrons to photons = mW

mW X eye sensitivity = how bright it appears.

So, the Dark Adaption Red emitter is much more efficient at converting electrons to photons... but in order for it to appear (your eye sensitivity) as bright as another, you need a lot more of it.

Makes sense the way you explain it..probably applies to CRI changes also I would imagine.

I think you're saying that different wavelengths of light are not sensed equally by the human eye. So perhaps it can simultaneously be true that the HDS Red is throwing more lux intensity (to the sensor) than other wavelengths at a given distance, but be harder for the human eye to discern at that distance? In other words, a red emitter can be both the best thrower and the best for OPSEC?

The (bio-)physics of the whole process is fascinating.

lion504 said:

I think you're saying that different wavelengths of light are not sensed equally by the human eye. So perhaps it can simultaneously be true that the HDS Red is throwing more lux intensity (to the sensor) than other wavelengths at a given distance, but be harder for the human eye to discern at that distance? In other words, a red emitter can be both the best thrower and the best for OPSEC?

Click to expand...

Exactly.

archimedes said:

The (bio-)physics of the whole process is fascinating.

Click to expand...

The graph above is also for the cones, not the rods. The graph shifts to the left when using rods (which actually only give you black and white vision but are still "color" sensitive.

@Hogo
Thank you for this interesting explanation!:bow::bow::bow: That explains also very well why monochromatic light is not measured in Lumens!

But the story is even more complex than what Hogokansatsukan could hope to describe. Take for example that eye sensitivity vs. wavelength graph. That's an idealized curve. Who knows what scientists have done / agreed among each other to arrive at that (not questioning their efforts there btw ). Your eye is not the same as my eye. Neither are the brain cells that process the signal. Operation of either may depend on silly things like what you have eaten yesterday. :laughing: Or how about this:

For light that is of the same wavelength (or same spectrum), the human eye is pretty good at spotting brightness differences. See for example how subtle / many shades of gray one could tell apart as being different from each other. But how about different colors?

Take a surface that's lighted blue, and a roughly similar lit red surface. How would you decide at which brightness levels "red" is exactly as bright as "blue"? In terms of measuring it, it's essentially radiated power per surface area. Possibly 'sorted' by wavelength or part(s) of the spectrum that are of interest. Sensors with known characteristics + calibration. But brightness as perceived by a human eye? Impossible imho - comparing apples & oranges.

Surely it doesn't end there. Like said: biochemistry (among other things).

It was simply to show why a 250mW and 900mW of different wavelengths can appear as the same brightness.
No intention of writing a doctorate thesis on it! LOL!
But yes, everybody is different. Just look at tint preferences (which I often relate to food taste).