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Light meter recommendations

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#1 teast

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Posted 15 April 2013 - 09:44 AM

Can anyone recommend a good, high-quality and accurate light meter to measure light trespass at the property line? I'm attempting to assist someone who feels the light falling on her property exceeds the allowable figure for her area but needs to quantify it.

I searched the forum for previous mentions but couldn't find any similar requests so suggestions are appreciated.

-Tom

#2 richard7

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Posted 15 April 2013 - 04:54 PM

Just do a web search for light meters. there's a bunch of them. You'll also find apps for both Iphone and Android.
The only problem would be in finding the regs, for your area.

#3 teast

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Posted 16 April 2013 - 09:44 AM

Thanks for responding Richard.

I have already done web searches and, as you said, there's a bunch of them and prices range from under $20 to over $400. That makes it difficult for someone like me, who is not familiar with light meters, to make an intelligent decision. So, maybe some more background would help.

I want to be able to accurately measure the light intensity from outside lights - streetlights, parking lot lights, wall packs, security lights, etc. So my question becomes, are some brands/models better suited for such measurements than others? Is it worth it to get a model that has settings for incandescent, fluorescent, mercury, sodium, metal halide, LED, etc. Some meters have memory, some have calibration routines. So, what are the important features to look for, for what I want to do? Is anyone here a lighting specialist who can recommend a model or what features I should look for?

Thanks, -Tom

#4 GlennLeDrew

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Posted 16 April 2013 - 06:42 PM

I have no expertise here, but do have a few notions on requirements.

You want to determine the light level incident at or near ground level. An incident level meter probably should have a white diffusing dome to intercept light from a hemisphere, or nearly so. Such a sensor is pointed straight up, to sample sources from all directions.

It must be pointed out that the foregoing methodology is appropriate for ground level illumination, the ground being generally tangential to the light source(s). In the case of light trespass where we are considering such cases as through windows, the meter should then be pointed toward the offending light.

As for units of measure, I should think foot-candles, cd/m^2 (candelas per square meter) or lux should suffice. In any event, conversions can be made, if necessary.

The meter should be reasonably sensitive, as we're considering 'nighttime' light levels. Off the top of my head, it should measure down to at least 1 foot-candle, and perhaps 0.1 foot-candle.

Assuming the meter is filtered so as to reasonably well approximate the visual system's spectral response, there should be no requirement to consider the light source type. We are not concerned at all with color balancing, like we might when taking images.

Just a few thoughts to (hopefully) guide the selection process...

#5 obin robinson

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Posted 16 April 2013 - 06:44 PM

I am very familiar with light meters. I built one years ago that was quite accurate. Check out the KEH site for some good deals on used ones:

This might work for you:

http://www.keh.com/c...1/sku-GM7099...

Call them and let them know what you are trying to do. They are very helpful with great customer service!

obin :cool:

#6 GlennLeDrew

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Posted 16 April 2013 - 07:18 PM

Obin,
There is no info on that web page. How sensitive is that meter?

#7 obin robinson

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Posted 16 April 2013 - 08:13 PM

Obin,
There is no info on that web page. How sensitive is that meter?


DOH! I was a bit quick on the trigger. That is an exposure meter meant for cameras. They are useful but I think you need something that measures lumens like this:

http://www.ebay.com/...-Lux-foot-ca...

I used an ancient version of the same thing. I built an analog version and calibrated it using a digital meter. The digital ones are ridiculously accurate. I bet the one in the eBay auction is 10x more accurate and 1/100 of the price of the digital ones I used in 1991.

Those are actually pretty useful. You can use them to figure out if you have proper lighting inside your house or workshop.

obin :cool:

#8 Illinois

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Posted 17 April 2013 - 06:58 AM

Little Dipper and Cancer are my light meter!

#9 teast

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Posted 17 April 2013 - 11:54 AM

Glenn, Obin and everyone else:

Thanks for your responses. Based on the comments so far here is what I'm gleaning from the conversation:

1. It is important to consider whether to use vertical or horizontal orientation, depending on the conditions being observed.

2. I don't need to spend a lot of money to get an accurate meter (most claim +/- 5% accuracy - is it worth it to go for 3%?)

The situation I'm looking into involves bright parking lot and security lights trespassing onto a residential property. The zoning code states no more than 0.5 foot-candle (5.382 lux) at the property line so I am thinking that a vertical orientation at the property line, facing toward the source is appropriate. The terrain is relatively flat between the source and the property line.

How important is it to block incident light from other sources? Should I consider some type of light shield or tube around the sensor to make sure I'm only measuring light from the target source?

Thanks guys - I'm learning a lot!

-Tom

#10 GlennLeDrew

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Posted 17 April 2013 - 01:13 PM

Tom,
Accuracy of 10%, even 20%, is more than fine in this application.

More important is sensitivity. You want to be confident that at the low end, where you're in the 1 foot-candle range, a reading to 0.1 f-c is not really in error of 0.2 or 0.3 f-c.

If the offending light is rather dominant, it may make little difference shielding other sources. But I suppose for maximum confidence in discrimination the 'bad' light, some kind of dark cylinder or cone protruding a few inches should do the trick.

#11 csrlice12

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Posted 17 April 2013 - 02:30 PM

If nothing else, put up a tarp between two poles or a Patio Umbrella between the lights and you. Helps some.

#12 obin robinson

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Posted 17 April 2013 - 05:14 PM

2. I don't need to spend a lot of money to get an accurate meter (most claim +/- 5% accuracy - is it worth it to go for 3%?)
-Tom


Yeah these things are pretty accurate. The least accurate ones from today beat the really expensive ones from years ago. If you want to measure light from one source just put the sensor in a short piece of a paper towel tube and aim it at that light.

Good luck!

obin :)






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