Using a light meter properly

[Fallingwater]

I bought a light meter. It seems quite a straightforward gadget, but having zero experience in this field I wonder if I'm missing something.

Basically I position the flashlight a meter from it, set the scale switch, point the middle of the beam at the detector thingie, turn off the light and take the measuring.

Is this correct?

Thanks.

 

[TedTheLed]

depends; is the receptor thingie an incident light receptor thingie or a reflected light receptor thingie?
an incident receptor would have some sort of plastic globe-type thingy over it, a reflector-type; not.
incidental light would be the light itself falling onto the object you want to photograph, which you measure by putting 'incident bulb' in the same light as the subject. the reflected light measurement would be taken by pointing the receptor thingie directly at the subject and measuring the light bouncing off of it.
obviously unless the flashlight beam is extremely even and homogenous all over it's field, neither of these methods will give you an accurate reading..
it would be better to shine the light on a white (or gray) wall, and take a reflected light reading from the wall, including the entire light field in the reading..

 

[Uncle Bob]

it would be better to shine the light on a white (or gray) wall, and take a reflected light reading from the wall, including the entire light field in the reading..

Make sure the gray wall is middle gray on a gray scale. Or buy an 18% gray card at a photo supply store and measure your reflected light off that.

 

[TedTheLed]

well not if you just want to take relative measurements of the brightness of flashlight beams.. if you want to actually take a well-exposed photo of the wall, then yes, take a reflected reading off a greycard held against the wall. or a few readings 'across the beam' with an incident meter pointing towards the camera, and average them...but that's not what you want to do..right?

 

[Fallingwater]

Right.

I have a hardware and gadgetry review website. I've only reviewed a few things so far, and then I had to leave it without new material for several months following serious family and personal problems, but I'll resume work on it shortly.

I got the meter because I'll be reviewing flashlights as well, and I want to be able to give at least vaguely objective measurements on their output. Something that goes beyond "pretty bright", in other words.

Oh, and the meter has a plastic cap on the receptor, so I guess it's incident light. It's this one.

 

[Uncle Bob]

well not if you just want to take relative measurements of the brightness of flashlight beams.. if you want to actually take a well-exposed photo of the wall, then yes, take a reflected reading off a greycard held against the wall. or a few readings 'across the beam' with an incident meter pointing towards the camera, and average them...but that's not what you want to do..right?

In Fallingwaters's original post he/she didn't mention photographing beam shots. If he/she wants to take pictures of flashlights as objects, then incident readings measuring light falling on the object is best.

Shooting beam shots is another story. I've never done that. I'd probably use a white wall and rely on my camera's reflected light metering and then manipulate values in my digital exposure to show relative light differences.

Did that make sense? :shrug:

Maybe others with more experience need to chime in here.

 

[robm]

I would suggest building a lightbox for total output comparisons, and use the meter at 1m, as you stated in the OP, for relative throw.

You could also then 'calibrate' these values against common lights to allow others to compare.

 

[TedTheLed]

In Fallingwaters's original post he/she didn't mention photographing beam shots. <snipped>

I bought a light meter. It seems quite a straightforward gadget, but having zero experience in this field I wonder if I'm missing something.

Basically I position the flashlight a meter from it, set the scale switch, point the middle of the beam at the detector thingie, turn off the light and take the measuring.

Is this correct?

Thanks.

basically yes, but I would turn the light ON before taking the measure.

personally for beam comparisons I like to see picutres of objects lit up by the lightbeam/s in question..using the same subject and exposure as far as possible..