Amprobe LM631A Light Meter, retail $89.95 (*)
Manufactured by Amprobe (
Last updated 12-19-10

I've had this for quite a few years now, that's why it does not look brand spanken new in the above photograph!!!

This product does not emit light of its own (much like this spectrometer, this spectrometer), and my beam cross-sectional analyser too) so the standard review format will not be used and the product will be assigned a rating at once. A very high rating too, as during the time I've had it, it has thus far performed pretty much flawlessly.

This is the Amprobe LM631A Light Meter (formerly known as the Wavetek Meterman LM631).
Its purpose is to allow you to measure the intensity of light in units of lux or foot-candles (switch selectable).

I've been using this meter since my Tektronix J16 Digital Photometer got destroyed in an earthquake in late-February 2001.

* This is a .PDF file; you'll need Adobe Acrobat or other PDF reader installed before you click on the link.

 Size of product w/hand to show scale SIZE

To use the Amprobe LM631A Light Meter, slide the switch on the front of the products body to the "lux" or "fc" position, remove the black plastic cap that protects the light input sensor, position the sensor exactly 12" (for foot-candles) or 1 meter (for lux) away from the light source under test, turn the light source under test on (thus irradiating the sensor with it), and note the reading on the product's LCD readout.

If you see "OL" displayed, that indicates that you need to press & release the rightmost button on the front of the unit. If you still see "OL", press & release it again. Do it once more if necessary; the "x10" indicator will now be shown, letting you know that you must multiply the displayed value by 10 to arrive at your final value.

The sensor head unclips out of the body of the meter; it is attached via a coily cord.
This allows you to place the sensor where the entire instrument might not otherwise fit.

The LM631A also comes equipped with a backlight for its display, allowing you to take readings with the meter body in a dark or poorly-lit location.
To engage the backlight, first turn the meter on. Press and hold down the center button (the one labelled "PEAK") for approximately two seconds, release it, and then press & release it again more quickly to return the instrument to normal functionality.

If the backlight is already on and you want it off, just do the exact same thing you did to turn it on in the first place.

Turn the instrument off when you are finished using it; do this by sliding the switch all the way to the lowermost position. And snap that black cap back over the sensor to help keep it clean and free of dust, dirt, dust rabbits, etc. that could affect the reading.

This product feeds from 4 AAA cells, which you supply yourelf. To install or change them, turn the unit over, use a small phillips screwdriver to unscrew & remove the screw holding the battery door on, slide the battery door off, carry it aqnd the screw to a bridge over deep water (the Brooklyn Bridge would be ideal; however, the Juneau-Douglas Bridge would also do in a pinch here), and throw them over the side so that they go "blub blub blub" all the way to the bottom of Gastineau Channel with all of the bowling balls that were lobbed over that bridge in the 1950s and 1960s...O WAIT!!! YOU'LL NEED THOSE!!! So just set them aside instead.

If necessary, remove and dispose of or recycle the four used AAA cells as you see fit.

Insert four new AAA cells into the compartment, orienting them so that their flat-ends (-) negatives face a spring for them in each compartment.

Slide the battery door back on, screw in that screw, and be done with it.
Aren't you glad that you didn't huck that battery door & screw over the side of the Juneau-Douglas Bridge now?

This is what the Juneau-Douglas Bridge looks like...or what it lookED like anyway before it was replaced in 1976.

And this is what the bridge looks like now.

Photograph of the unit's LCD with the backlight LEDs turned on.

Spectrographic analysis
Spectrographic analysis of the yellow-green LED backlight in this meter.

Spectrographic analysis
Spectrographic analysis of fluorescence of the orange body of this instrument when irradiated with the Wicked Lasers Spyder 3 Arctic 445nm 1W Blue Diode Laser (2).

USB2000 spectrometer graciously donated by P.L.

Video clip on YourTube showing how this instrument might be used.

This clip is approximately 3.90056743862 megabytes (4,059,306 bytes) in length; dial-up users please be aware.
It will take no less than ninteen minutes to load at 48.0Kbps.
I cannot provide it in other formats, so please do not ask.

Test unit was furnished by a fan of this website and was received sometime in 2001.

Product was made in Taiwan.
A product's country of origin really does matter to some people, which is why I published it on this web page.

UPDATE: 00-00-00

    PRODUCT TYPE: Light meter
    LAMP TYPE: LED backlight
    No. OF LAMPS: 4
    SWITCH TYPE: Pushbuttons & slidfe switch on top of product
    CASE MATERIAL: Plastic
    BEZEL: N/A
    BATTERY: 4x AAA cells
    CURRENT CONSUMPTION: Unknown/unable to measure
    ACCESSORIES: None that I'm aware of
    WARRANTY: Unknown/not stated


    Product was not intended to be a light-emitter, so the traditional "star" rating will not be used.

Amprobe LM631A Light Meter *

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