How to read light level with an SLR camera?

Added by: 10k Last edited by: 10k Viewed: 402 times Rated by 8 users: 6.83/10Contributed by: ngc7579
submitted February 15, 2003

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".