Light Power Ratio (Stops)
Find the stop difference between two lights set to different power levels.
About Light Power Ratio (Stops)
Because light power and stops have a base-two relationship, halving a light's power is exactly one stop less output. Balancing strobes relies on setting power ratios in stops, which is the language the flash meter and the eye share.
Formula
Light Power Ratio (Stops)
Stops = log2(Light A power / Light B power)
- stops
- Halving power drops output by one stop
Worked example
With the default values below, Light Power Ratio (Stops) returns Stops Difference of 1.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Light A powerminimum 0.1
- 100
- Light B powerminimum 0.1
- 50
Results
- Stops Difference
- 1.00
- Power Ratio
- 2.00
- Which Is Brighter
- Light A is brighter
Step by step
- 1Values used
- 2Light Power Ratio (Stops)
- 3Stops Difference= 1.00
- 4Power Ratio= 2.00
- 5Which Is Brighter= Light A is brighter
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Light Power Ratio (Stops) calculated?
Stops = log2(Light A power / Light B power) Because light power and stops have a base-two relationship, halving a light's power is exactly one stop less output.
Why does Light Power Ratio (Stops) matter?
Balancing strobes relies on setting power ratios in stops, which is the language the flash meter and the eye share.
What values do I need to enter?
This calculator takes 2 inputs: Light A power, Light B power. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.