# Recalculating lux or lm from EV [duplicate]

I have to calculate amount of light from IR emmiter. The only equipement, that I can use is Sekonic Light Meter like this one: http://www.ebay.com/bhp/sekonic-l-358

The problem is that i need to have the light level in lux or lm, and the metter gives me the values in EV. Could anybody tell me how could I recalculate those results: 11,6EV 11,4EV 11,1EV 10,4EV 9,3EV

• – godfatherofpolka Apr 15 '15 at 13:37
• Note that lux and lumens are fundamentally very different things: a lumen is a measure of the total amount of light, whereas a lux is a measure of light per unit area. Your light meter can measure light per unit area (or lux), but it can never tell you the total amount of light emitted (lumens). – Philip Kendall Apr 15 '15 at 13:47

You probably will have trouble for your purposes improving on this

"Close enough"*

• Lux = 2.5 x 2^EV

• EV = log_2(Lux/2.5)

ie 2 raised to the power of the EV value and multiplied by a constant.

*_The above Seconic table best fits about Lux = 2.502442 x 2^EV

2.5 will be fine enough for mere mortals.

A bit of Googling turned up this Stack Exchange question & answers from 2011 - I need not have bothered :-)

Wikipedia's Exposure value entry is well worth reading. I got that link from the prior Q&A!. Note that the value of 2.5 or 2.502442 or ... is a compromise one and relates, among other things, to the flatness of the subject and the degree to which light is reflected off it back towards the source and also to the sensor shape (eg flat (with cosine response ie effective incident light is the normal component which is proportional to the cos of the incident angle) or hemispherical with cardioid response (you don't really expect me to try and explain that, do you ? :-) ) . [It almost makes sense on inspection].

Notes:

Lux = k x log(EV)

Lumens = Lux x Area_illuminated or, more usually,

Lux = lumens per area

A light level of 1 EV requires 1 second exposure at 1/100 th second at f/1 with 100 ISO sensor sensitivity.

There are some applications, that run on the Android OS, that calculate the equivalence between the EV and light energy per unit area (in lux, never in lumen as CherryCola has already answered). They also measure and give the value as a normal photometer, using the camera sensor of the Android device on which they are installed. Some are free, some not. I use LigthMeter Tools, really good (the price is about three euros and is installed on any Android device registered to your name).