Quality Property of Light

Kissed by the sun

I have wrote about the Quantity and Color properties of light which we have tools to evaluate. The next two properties of light, Quality and Direction, we have to judge with our eyes. Luckily our eyes are a good judge even though our judgement will be done as a degree when it comes to the Quality of Light. Quality of light has two terms, Specular and Diffuse, which we use to describe how hard or soft the edges of the shadows are. As with color we need to include surfaces that the light is falling when we discuss Quality of light. A specular surface could be described as mirror like while a diffuse surface would scatter or disperse light falling on its surface. A specular light is a point source which creates hard edged shadows while a diffuse light is a large area of light radiating in many directions creating soft edged shadows. The Specular Diffuse relationship is a function of the size of the light source and the distance from the subject. A good example of this is the sun, it is very large but being 93 million miles away makes it a specular light source. On the other hand the sky is a very large and surrounds us so it would be considered a diffuse light source.

Surfaces can change when illuminated by different light sources. A Specular surface can become more diffuse when lit with a very diffuse light source such as a very large close softbox. Like wise a diffuse surface lit with a small spot light can take on a more specular type look. The important thing to remember is specular and diffuse are at far ends to each other and there is all degrees between these two extremes.

Here is an example if making the properties of light work for you. Take a crystal wine glass and put it on a white background Put a softbox close on one side of the wine glass and a white card close on the other side and observe what this lighting does. This is called white line lighting. If you look close the edges if the glass have a white line and you also have a pleasant highlight on the softbox side and if the card is close enough and secondary highlight. Movement of the light forwards and back will make a nice fine adjustment to the highlights. I should use this example in the blog under the direction property of light but I needed to use it here to show how diffuse light on a specular surface behaves. I will use this same example in my blog when I cover the direction property of light so keep this in mind.

The important thing to know about the Quality of light is that it is a function of size and distance in relation to the subject and can be judged by the edges of the shadows. Contrast is also related by the relationship if surface and quality. A diffuse surface illuminated by a specular light source will be more contrasty than if it was illuminated with a soft diffuse light source. We can not separate the size and distance factor. A face illuminated with a softbox or umbrella let’s say a 2 feet will be much softer than if the light source was at 5 feet. Placing a diffuser over a small on camera flash does not make for a diffuse light. Even adding a small softbox does not do much without moving closer to the subject. Bouncing your flash off a ceiling or a wall helps as the area you bounce from becomes a large light source.

Now that we have a better understanding of the quality of light property I will blog on the direction of light property. I hope you enjoyed this blog and will subscribe so you don’t miss the next one. Thanks for taking the time and reading.

About John Aydelotte

I aspire to pass on some of the 40 years of imaging knowledge I have acquired. I have a true passion for imaging and wish to enjoy my retirement from Commercial Photography by creating images from my heart. I am still taking a few Freelance jobs but would love to teach and lead others on their amazing photography journey. I have two grown children and 7 grandchildren. I am focusing on photography, education and retirement.

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