How to Calculate Contrast Ratios for More Professional Lighting Setups

How to Calculate Contrast Rations

Comments

Additions to your fine lighting article

filmutah's picture

I really liked your article about lighting contrast ratios, which is a topic that few people seem to know or understand, yet is extremely useful when figuring out the lighting style of your interview picture. This technique is most common when lighting actors in dramatic scenes, but it is also useful for lighting serious documentary interview subjects. In fact, I always teach this technique in my own documentary production classes. It helps people better understand how they can control the light and the look of their interview. Yet, there are a few things that I might add to your great article.

Instead of using F-stops for calibration, I would try using foot-candles, which is an easier and more precise way to compute the actual lighting ratio. However, you must measure the fill and key lights separately because there is a lighting overlap on the face and by measuring them separately you can get the precise value for each. You measure with the lightmeter next to the face pointed at the light source.

The computation is done by measuring the key light alone and then measuring the fill light alone and adding these foot-candles measurments together. To get the lighting ratio you divide the fill light measurement into the sum of the key and fill light measurements together.

For example, you measure the fill light at 40 foot-candles. You then measure the key light at 320 foot-candles. You then add these two figures together, which equals 360 foot-candles. The ratio is obtained by simply dividing the fill light foot-candles (40) into the sum of the fill and key light together (360), which is 9 (40÷360=9). So, our exact lighting ratio is 9:1, which would render a very nice film noir, dramatic look to your interview subject, indeed.
Brian Patrick, Professor, Film & Media Arts Dept., University of Utah

Additions to your fine lighting article

filmutah's picture

I really liked your article about lighting contrast ratios, which is a topic that few people seem to know or understand, yet is extremely useful when figuring out the lighting style of your interview picture. This technique is most common when lighting actors in dramatic scenes, but it is also useful for lighting serious documentary interview subjects. In fact, I always teach this technique in my own documentary production classes. It helps people better understand how they can control the light and the look of their interview. Yet, there are a few things that I might add to your great article.

Instead of using F-stops for calibration, I would try using foot-candles, which is an easier and more precise way to compute the actual lighting ratio. However, you must measure the fill and key lights separately because there is a lighting overlap on the face and by measuring them separately you can get the precise value for each. You measure with the lightmeter next to the face pointed at the light source.

The computation is done by measuring the key light alone and then measuring the fill light alone and adding these foot-candles measurments together. To get the lighting ratio you divide the fill light measurement into the sum of the key and fill light measurements together.

For example, you measure the fill light at 40 foot-candles. You then measure the key light at 320 foot-candles. You then add these two figures together, which equals 360 foot-candles. The ratio is obtained by simply dividing the fill light foot-candles (40) into the sum of the fill and key light together (360), which is 9 (40÷360=9). So, our exact lighting ratio is 9:1, which would render a very nice film noir, dramatic look to your interview subject, indeed.
Brian Patrick, Professor, Film & Media Arts Dept., University of Utah

I really liked your article

filmutah's picture

I really liked your article about lighting contrast ratios, which is a topic that few people seem to know or understand, yet is extremely useful when figuring out the lighting style of your interview picture. This technique is most common when lighting actors in dramatic scenes, but it is also useful for lighting serious documentary interview subjects. In fact, I always teach this technique in my own documentary production classes. It helps people better understand how they can control the light and the look of their interview. Yet, there are a few things that I might add to your great article.

Instead of using F-stops for calibration, I would try using foot-candles, which is an easier and more precise way to compute the actual lighting ratio. However, you must measure the fill and key lights separately because there is a lighting overlap on the face and by measuring them separately you can get the precise value for each. You measure with the lightmeter next to the face pointed at the light source.

The computation is done by measuring the key light alone and then measuring the fill light alone and adding these foot-candles measurments together. To get the lighting ratio you divide the fill light measurement into the sum of the key and fill light measurements together.

For example, you measure the fill light at 40 foot-candles. You then measure the key light at 320 foot-candles. You then add these two figures together, which equals 360 foot-candles. The ratio is obtained by simply dividing the fill light foot-candles (40) into the sum of the fill and key light together (360), which is 9 (40÷360=9). So, our exact lighting ratio is 9:1, which would render a very nice film noir, dramatic look to your interview subject, indeed.
Brian Patrick, Professor, Film & Media Arts Dept., University of Utah