Term
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Definition
| Photometrics is the study of the properties of light, particularly intensity, using math. |
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Term
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Definition
| It is a physical entity that we can observe and experience; simply put… time and money. |
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Term
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Definition
| Throw distance is how far the light is from the focus point. The throw distance (td) is the hypotenuse of a right triangle formed by the floor and the height of the structure the light is hung on. |
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Term
| What formula is used to find the throw distance? |
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Definition
Pythagorean theorem A2 + B2 = C2
The formula can also be written as:
Throw Distance2 = Vertical Distance2 + Horizontal Distance2
or
td2 = vd2 + HD2 |
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Term
| What is the formula to calculate beam diameter? |
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Definition
Beam Diameter = Multiplying Factor x Throw Distance
or
bd = mf x td |
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Term
| What is the mf of a fixture based on? |
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Definition
| The multiplying factor is a number we get from the manufacturer but it is derived from the field angle and is calculated by taking 2 times the tangent of the field angle divided by 2. |
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Term
| Where do you find the mf of a fixture? |
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Definition
Number comes from the manufacturer.
mf = 2(tan FA/2) |
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Term
| Why do par lamps have 2 mf values? |
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Definition
| A par has 2 mf values because it produces an oval beam of light. |
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Term
| Why are there two mf’s for a par lamp? |
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Definition
| Because the light is oval |
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Term
| What does td stand for in the above formula? |
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Definition
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Term
| How would you determine the number of fixtures needed to light a stage? |
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Definition
| By calculating the photometrics of a fixture we can see if a fixture will produce a large enough pool of light to cover a focus area. Using the beam diameter, we can determine how many fixtures are needed to light the stage. |
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Term
| If you determine you need 6.2 fixtures to cover the width of a stage how many fixtures would you use? |
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Definition
| You will need 7 fixtures to cover the width of the stage. |
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Term
| Why would you use the number of fixtures you specified in the previous question? |
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Definition
| It is because a light cannot split into fractions. It is better to have too much light then not enough. |
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Term
| What is the peak candela of a fixture? |
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Definition
| The peak candela is a number we get from the manufacturer and cannot be measured or calculated in the field. |
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Term
| What unit is peak candela measured in? |
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Definition
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Term
| What formula is used to determine intensity of a light source? |
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Definition
| The formula to find the intensity is footcandles equals the peak candela divided by the throw distance squared or fc = pc / td2 |
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Term
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Definition
| The intensity of a light source is measured in footcandles. The footcandle is based on how much light is found 1 foot away from a candle of a specific composition with a certain burn rate. |
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Term
| What is a correction factor? |
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Definition
| The correction factor is the percentage of the peak candela from a fixture when using a lamp other than the standard. |
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Term
| What does the transmission value of a filter tell you? |
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Definition
| The transmission value is the percentage of incident light that passes through a filter. |
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Term
| How do you determine the fc of a light that is using a non-standard lamp? |
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Definition
| There are two factors that will change the footcandle output of a fixture, one is using a filter the other is using a non-standard lamp. To find the intensity of the light in either of these cases you first find the fc output with the standard information and then multiply by either the transmission value of the filter or the correction factor for the lamp. Transmission values are found in the gel swatch book and correction factors are found on the fixture data sheets. |
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Term
| What is standard voltage? |
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Definition
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Term
| How do you determine the amps needed to power a lighting rig? |
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Definition
| When determining the power draw of your lights assume that all the fixtures will be run at full and multiply the number of fixtures by the wattage of each fixture. Add all the watts together and divide by 120v to calculate the total amp draw. |
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Term
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Definition
| This rule states that you should only use up to 80% of the total available amps leaving you with 20% for headroom. |
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Term
| What are the standard disconnect sizes? |
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Definition
| Standard size disconnects are 100A, 200A, 400A, 600A and 800A.. When figuring out what size disconnect a rig requires it is important not to exceed 80% of the available power. |
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Term
| What does the rating of a disconnect mean? |
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Definition
| Most venues are equipped with disconnect boxes for shows to tie into to get power. A disconnect box can be single phase or three phase and is rated at amps per leg of power. A 200A single phase disconnect would have 200A per leg for a total of 400A while a 200A three phase disconnect would have 200A per leg for a total of 600A. |
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