# Using Lux Meter??

Just bought a lux meter. My question is how exactly do I use it to get an accurate reading on my lights. Thought I heard that your suppose to keep it about a foot away to get an accurate measurement?

The standard is 1 meter, you can mount the meter (or sensor if its remote) and shine the hotspot around at the sensor. [I believe] you can take the highest reading but I’m not 100% on that, some meters will record multiple samples and average them for you or yo could average them yourself.

I too just got a meter but it’s out for calibration so I’m still using a cheapie (new one is an ExTech LT300 and it’s returned to the MFG are NIST calibration, old meter is an HS1010A) it’ll be interesting to see how accurate the \$18 china meter is.

What’d you get?

since the type of lights you are using are primarily thowers use this method. And regardless, the farther away you measure the more accurate the results.

make sure the room is as dark as possible any light contamination will skew the results. Take some tape and tape the sensor to a wall. Get a tape measure and set your light being tested 3 meters or 118 and 1/8 inches from the sensor. Be careful to keep the beam perpendicular(square) to the sensor as possible. Set your meter for X10. turn the light on, find a solid surface to set the light on, and point it at the sensor. move the hotspot around til you get the highest reading.

then multiply that(lux) x10 to get the lux at 3 meters. and then to convert it to lux@1m multiply that number times 9. because Candela(Cd) is lux times distance squared. 3m squared is 9.

Example: your red c8 pointed at the sensor with meter set to X10 reads 150.

150x10=1500 lux@3m
1500x9=13,500lux @1m or 13.5 Kcd

five meters is even better if you can find a place to get the distance. you would multiply by 25 instead of 9. because 5 squared is 25.

note: using one meter is the easiest but least accurate because the beam profile of the type lights you will be testing hasn’t settled into its final shape. Distance is critical, get as close as possible to 1m , 3m , 5m whatever you choose. even +/- 1/2” makes a big difference in the readings.

You will also notice that at initial start up the lux is high and starts to drop.It will most likely stabilize after 1-3 minutes. How far it drops is a good measure of how well your light is performing from the thermal perspective. When i first started building lights with color emitters a 25% drop was not uncommon. Now, if its more than 2% if find out why and fix it!