Acrylic Light Diffuser Effect on Lumens

When used in photography, diffusers soften the edges of shadows cast by lights, scattering the light's rays and minimizing harsh shadows in photographs. While factory-made diffusers are available, you can create a simple, effective equivalent using a sheet of acrylic.

Description

Lumens are a measurement of the intensity of a light source. Unlike watts, this unit measures the perceived brightness of a light source rather than the power the source draws, making it easier to compare the luminance of difference light sources with varying wattages.

Effects

Whenever you attach a lighting modifier to your light, the lumen rating will be reduced as the diffuser absorbs some of the light's energy.

Significance

Because of its thickness and crudity, the acrylic diffuser absorbs more light than a professional equivalent, requiring exposure compensation or brighter lights.

Calculations

With a reliable light meter, you can calculate how much light the acrylic diffuser absorbs. Set a bare light up and take a reading with your light meter, taking note of the f-stop and shutter speed readings. Attach the acrylic diffuser to the light and take the same measurement. The difference in exposure illustrates the amount of light lost by the diffuser.

References

• NPL: Lighting Now Labelled in Lumens; Aug. 2010
• iDigital Photo: A Guide to Measurement in Photography, Part One; Dec. 2008
• Alien Bees: Lighting for Still Photography; Paul C. Buff