# Can I use Ceiling Bounce Test ?

#### NotSoBrightBob

##### Newly Enlightened
Newb here and I found alot of threads when I searched that discussed using a CBT but I'm trying to understand if is useful to my untrained eye.

I think I understand how it works to compare two lights. Stand them both up equal distance from and facing a white ceiling. Shine both lights at the ceiling then "measure" the amount of light on the floor.

My question is how do I perform the measurement, is this some type of equipment that does that or is it a subjective matter. "Gee that one looks brighter than that other one."

Or...is there another simple test to compare brightness between two lights that doesn't require equipment.

Thanks for the education or link to a thread that I couldn't find from the google list.

Bob

#### GreySave

##### Enlightened
Welcome Aboard!

For most folks it is an eyeball test for total output. If you have a light meter or similar device it could of course be used.

#### Marduke

##### Flashaholic
+1

Most people just eyeball a subjective comparison. A few use a light meter set on the floor for a more quantitative measurement.

#### StarHalo

##### Flashaholic
The ceiling bounce is the easiest test to compare pure output between lights. If you just shine a light at a wall and look at the beam, how broad or narrow the beam profile is can fool your eyes into thinking the light is brighter or dimmer than it actually is.

The way I do a ceiling bounce: In a totally dark room, I grab a pair of lights and turn both on, and press both against my thigh or chest so the light from both is totally blocked. I then close my eyes, point light A at the ceiling, and looking straight forward I open my eyes and judge how the room looks. Then I close my eyes, block light A and point light B up, then open my eyes again, and can quickly see any differences. I can go back and forth between the two if they're close in output.

#### Patriot

##### Flashaholic
I only use it as a comparative test and sometimes use my cheap light meter to get a relative value. The ceiling bounce is actually pretty good at determining which of two lights is brighter. I use the alternating technique where I turn one light off and the other one on....switching back and forth every 2-3 seconds. I usually look around at the different walls to determine how much light is being reflected off of them.

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#### cerbie

##### Enlightened
Usually it's a comparative gut-reaction test.

The beam of a torch can fool your instincts. FI, I've now got a new EX10 GD+. in comparing by looking at stuff, it doesn't seem nearly as bright as my old beat-up, use-around-the-house, custom diffused ('cause the factory UCL broke in a fall) P4-bin Fenix L2D-CE (the brightest I've had, until two days ago, since I'm not lumen-hungry).

Well, one is really lighting up a wide area, where the other is putting most of the light into a small spot. So the spot just looks washed out. Alternatively, my eyes will sometimes adjust their brightest 'white' to the hotspot of a beam, so it looks very bright when it's not (ambient light, what you're looking at, color temp, and many other factors affect how your eyes react). Two outputs of different tint can also look like different amounts of light, when compared directly (this applies greatly to LEDs, and any gas-excitement type emitter).

Hmmm.

Well, if you point it at a white ceiling, the white color, and general texture, reflect and diffuse the light output. The amount reflected tents to be a certain ratio of light pointed to the ceiling. This allows for a decent eye-ball test of different torches.

Reading paper from ceiling-bounced beams, my new torch looks a bit brighter, which should be the case (IE, lots of time at 700mA with poor heatsinking, and extra losses from custom window, on the L2D).

##### Flashlight Enthusiast
Snap a few shots with a cam set to a fixed exposure and compare the pics.

#### KiwiMark

##### Flashlight Enthusiast
I have done this test with each light I have - often you can quickly see the difference in output easily.

With my 4D Maglite w/Malkoff I can easily read the small writing in my motor scooter workshop manual from the reflected light (but not the direct light - way too bright!). My Olight also lights up my room really well, the R2 LED throws out a lot of light on full power from 2 x 16340.

Any camera shop would have a hand held light meter capable of giving a reading of the ambient light. Also a camera pointing at a wall will give a good idea by what shutter speed it can use, its automatic settings will change with the amount of light available. So far I have only bothered to use my eyes and see how well I can see small details with my different lights.

#### NotSoBrightBob

##### Newly Enlightened
Thanks for the education. Did a little more playing this weekend and yes I can tell the difference amongst many of my lights.

I love this place!

Bob