Test 1 - Light Sources and Filters

Neutral Density Filter

Also called optical density filter, its a filer that blocks out all wavelengths of the SPD evenly proportionally. These filters are often used in photography when wanting to use a certain exposure setting and reducing the amount of light coming in. ND filters are measured logarithmically. ND 1.0 means that it reduces light down to 10% transmutation. ND = 2 - log(transmittance %) ND = log (1/transmittance decimal) Every change in 0.3 log units results in increase/decrease of 2x.

Filters

Any material that subtracts from the SPD of a light source. Filter's can't add any additional light. When a filter appears blue, that means its letting blue light through and absorbing all the other light.

Black Body Radiator vs Grey Body Radiator

Black body radiator, full radiator, Planckian radiator. Gives off light though the emission of heat. The spectral output is defined by the temperature spectrum (continuous spectrum). As the color temperature increased, the peak of the spectrum shifts left and the light given off appears more blue Grey body radiators are similar to black body radiators but are less efficient in their absorption and emission.

Bandpass Filter

Broadband: Allows a wider range of light through in the middle, while blocking wavelengths on either side (longer and shorter wavelengths) Narrowband: Allows a narrow range of light through in the middle, while blocking wavelengths outside this range.

Color Temperature

Description of the light emitted from a black body radiator. The hotter the color temperature, the more blue the "white" light appears. This can be applied to incandescent bulbs. Correlated color temperature is used to measure color temperature for another light source that's not a black body radiator (fluorescent/LED)

Notch Filter

Filter that blocks out a specific segment of wavelengths. Are often used in laser safety goggles.

High-Pass Filter

Low-cut filter. These filters cut off shorter wavelengths and allow longer wavelength through. These can be seen for nighttime driving glasses or sports/computer glasses.

Low-Pass Filter

High-cut fillers. These filters cut off longer wavelength lights and allow shorter wavelengths through.

Incandescent Bulbs

Light bulb that emits light due to heat (thermal radiation). This is produced by running an electric current through a filament. The temperature of the wire is exactly related to the color temperature of the bulb. Incandescent bulbs behavior similar to black body radiators such that the energy given off of the bulb is given off as heat.

LED Source

Light emitting diode works through electroluminescence. This is a process where photons are directly released from electrons passing through a material.

Fluorescent Bulb

Lightbulb in which electricity passes through a gas. This excited gas produces UV light that reacts with the phosphor lining the inside of the bulb. The phosphor absorbs the UV light and reemits it as visible light.

Spectral Power Distribution (SPD)

The curve that illustrates the color profile, or wavelength intensities, for a light source. By looking at how much energy is emitted outside the visible spectrum, you can see how efficient the bulb is. Illuminant A is an incandescent bulb.