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LED Apparent Brightness?

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Hi,

Integrating light sphere :)
 
On a cloudy day or at dusk when there is a Jeep thing or other Chrysler car approaching me with its full brightness high beams used as daytime running lights then the entire spheres of my eyeballs blindingly light up.
My car shines its dimmed low beams daytime running lights on the ground, not straight at oncoming drivers.

I notice that new VW and Kia cars also use undimmed high beams as daytime running lights.
 
I have an eye weighted Lux meter and have designed and built a goniometer for measurement of LED's and have performed numerous experiments. The eyes can detect very small levels of modulation and the comparison to steady state is inverse to rate of change and depth of modulation. For example if the rate is very slow or in minutes, the acuity of discerning 50% change in intensity is very poor. Also if the rate of carrier modulation is too fast (kHz) , it is very poor at detecting modulation at 50%. However if at slow modulation with step changes , 1 Hz it is easy to detect a 1 %. But if they are side by side 10% is barely noticeble difference.

So the conclusion is the modulation is the key to perception and flicker of 100% modulation is very noticeable especially when either the LED or eye is moving. ... Which is why Engineers who made the 1st brake lights for Cadillac made an obvious mistake assuming 500Hz PWM was adequate for a fast moving car when braking moving across the observer's view rather than just in front. The result was dots of light impinged on the retina for several mililliseconds which appeared like a Red stroboscope. They increased the PWM rate in following years. Perhaps to 3kHz.

For my instrument , I had 7 eye-corrected 5mm photo diodes from Panasonic which were recessed in stepped apertures inside black mounting cubes to minimize ambient light with an effective flat response of 10cm at 1m distance but steep rejection of light outside that aperture of and measure the LED intensity at 0,5,10,15 deg angles in both XY directions for testing to BAPT German road safety illuminationn standards. The outputs were powered by 5V LDO and selected to an inbuilt DMM. The stepped conical black surface at the box interface (like that used in all good camera lenses) minimized the surface area for stray ambient light getting into the photodiode lens.

Also consider that nearly all computer graphics cards only use 8bits for intensity of each colour and only a calibrated Lux meter can tell the difference of 1/256 level changes. I am usually happy if my LCD TV and 24" monitor are matched for gamma and colour balance within 5%.

Also interesting is that most LCD TV 's and even some video Adapter DAC's have poor calibration and non-linear step size. One of the easiest ways to view colour balance is to observe the Win7 boot logo with the RGBY modulating colour "Windows" and compare the size of each window. if each are symmetrical in size, your monitor and color-blindness are calibrated. If one is much smaller, it isn't calibrated. But I prefer using DPT.exe with gradient colour intensity patterns to check for saturation and black level.
 
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