How to Read Light Level with an SLR Camera?

Using your SLR camera in manual mode, you can measure light level:

* Set camera ASA speed to 200.

* Set camera shutter speed to 1/125.

* Hold a large, white card (or sheet of paper) in the proposed plant location so that it gets max illumination.

* Be sure that nothing but the white card is showing in the viewfinder.

* Adjust f-stop on camera (or lens) until camera meter reads "correct exposure"

f4 = 64 foot-candles
f5.6 = 125 foot-candles
f8 = 250 foot-candles
f11 = 500
f16 = 1000
f22 = 2000
f32 = 4000

I use this technique to:

* Determine "hot" spots in the room - I put my youngest plants there.

* Determine "weak" spots - install reflectors as needed to bring up light levels.

* Determine when bulbs are getting weak - instead of "it looks dimmer than before".

Author: ngc7579

I use a cheap sub $15 light meter to do this. Very worthwhile, especially for making sure light is even.

Phone apps

I try to keep apps off of my phone. Even an app that would check the light level can be gathering data on the user. A little something call 'Data Analytics', part of the booming world wide business in Surveillance Capitalism.

I inherited a really old SLR which came with a hand held light meter so it might be something else interesting to try.