The Shower Test - can you spot PWM?

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ToyKeeper
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The Shower Test - can you spot PWM?
A. Left=PWM, Right=PWM
61% (57 votes)
B. Left=PWM, Right=Constant
13% (12 votes)
C. Left=Constant, Right=PWM
19% (18 votes)
D. Left=Constant, Right=Constant
7% (7 votes)
Total votes: 94
ToyKeeper
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I often hear people suggest the shower test as a way to detect whether a light uses PWM or if it delivers constant current. The test is: Shine the light at fast-moving water, like a shower head. Then look for dotted lines. If it has dots or spots, it uses PWM. If the streaks are smooth, it’s constant current.

But I find the test unreliable and error-prone. So I took some pictures of how this test looks in real life, and I want to know if people can determine the correct answer.

Here’s the pic. The poll choices refer to this picture:

Both lights were running at 30 lm, and both pictures used the same camera settings. Clicking the picture provides a larger version.

Edit: The answer is here.

ChrisGarrett
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Neat! I voted CC for the left and PWM on the right.

Chris

Poguche
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I voted for both, as they have dotted lines that look very artificial to me.

Lexel
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did this a long time ago, like 1m below shower head its a lot better to see

with the right shutter speed you can even get very close to the PWM frequency with calculation of drops/shutter speed

djozz
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If the only light source on rhe shower has PWM you should see it in all water beams, not just in some. So in both pictures the shower is illuminated with a non-PWM light source, or too fast to even notice this way.

I guess..

Nice pic Lexel Smile

MtnDon
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I have trouble telling from that photo. I use a bicycle hanging in the garage; spin the front wheel and shine the light at the spokes. The bike is always there unless it is being ridden. If it’s being ridden I probably have little interest in checking PWM right then. Big Smile

BurningPlayd0h
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For the poll would “PWM” be any at all, or PWM at a frequency slow enough for a human eye to see it?

ToyKeeper
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BurningPlayd0h wrote:
For the poll would “PWM” be any at all, or PWM at a frequency slow enough for a human eye to see it?

Any PWM at all.

But, specifically, the kind which pulses on and off. Not the kind which stays on but does a square wave oscillation between two different levels.

DavidEF
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I voted left=constant, right=pwm. But I’m really unsure.

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Relampago
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Norman Bates would know.

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CREEXHP70LED
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I think TK is playing a trick on us and one or both are not using PWM. I would normally say right and left is both PWM, but I think the trick is left is no PWM and right is PWM. Possibly no PWM at all.

 

 

 

Scallywag
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I can't tell. I'd use a control picture as reference, and compare, if this were my test.

To test for visible PWM, I use a fan. After that, I use a camera with very short exposure time Wink

pinkpanda3310
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Streaks and dots in both pics to me Question

  

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This…

ToyKeeper wrote:
…But I find the test unreliable and error-prone. …

It is.

I use the manual control on my camera/phone camera to check for any “flickering”, normally between 1/1000 to 1/2000 exposure the “flickering” will show clearly. I’m awfully sensitive to mid to low frequency “flickering”, even those that claims by some as “high-enough” or not PWM in its strict sense. For me, it doesn’t matter whether it’s On-Off or “Stay-On but does square wave”, as long as it’s not constant current, it’s being put to “flickering” category for me. Big Smile

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Nicolicous
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pinkpanda3310 wrote:
Streaks and dots in both pics to me Question

yup both have PWM but the right pic is worst Smile

Nico -.-

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…and what about the streaks?

It’s like there’s 2 light sources. I get that the water droplets can move at different speeds which isn’t accurately represented with a still picture. But as pointed out by TK it seems like a pretty flawed test.

  

Nicolicous
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oh I didnt see that Silly

Nico -.-

SKV89
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I shine a light at my spinning usb fan to test for pwm. Works well

gchart
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Is it just me, or is there a face in the water on the right side? Creepy! Shocked

CREEXHP70LED
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gchart wrote:
Is it just me, or is there a face in the water on the right side? Creepy! Shocked

There is a face there for sure.

 

 

 

Lightbringer
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gchart wrote:
Is it just me, or is there a face in the water on the right side? Creepy! Shocked

Looks kinda like a caricature of Stan Laurel with his little hat.

Kind of a mirror-image of

 

Anyhoo, when I put my face close, stare at the image, and kinda go cross-eyed, I kinda see a 3D image of a swan.

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BurningPlayd0h
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The dots in the second picture aren’t necessarily PWM, they just look like the “ripples” in a stream of water reflecting light at different angles to me.

wle
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all you have to do is wave your finger back and forth rapidly, in the beam

or point at a rotating ceiling fan

wle

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BurningPlayd0h
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wle wrote:
all you have to do is wave your finger back and forth rapidly, in the beam

or point at a rotating ceiling fan

wle

There’s zero chance someone will be able to see 10kHz or faster PWM doing that.

fonfan
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Fast movement of light source – the best PWM test.

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wle
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BurningPlayd0h wrote:
wle wrote:
all you have to do is wave your finger back and forth rapidly, in the beam

or point at a rotating ceiling fan

wle

There’s zero chance someone will be able to see 10kHz or faster PWM doing that.

maybe but

a. at that frequency, isn;t it imperceptible?
b. would the shower test work for that, assuming PCM/no PCM matters at that frequency?

"You never have the wind with you - it's either against you, or you're having a good day."
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Relampago
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Ha ha. It was a trick question. She’s not even using a flashlight.

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gchart
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She’s screwing with us… “PWM” are the initials of the person whose face is on the right side Wink

CREEXHP70LED
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Lol…..Selene is playing a game for sure… Big Smile

I just read her response. Sounds like both are PWM however, just at different frequencies or types…. Silly

 

 

 

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