light sensor & colorimeter

Often used elaborately to produce a makeshift colorimeter, the light is very useful for many biology and chemistry experiments on rates of reactions. As monochromatic light is less important with turbid solutions the makeshift colorimeter seems adequate for measuring the speed of precipitation reactions. Some have a linear response that suits them better to quantitative work such as showing the inverse square ‘law’, some have a logarithmic response which is perfectly adequate for other, more general uses. For example, you could use almost any light sensor device as a marker sensor to show day and night. They vary in their response, for example an LDR type responds more slowly than a diode type. The faster type can pick up the AC ripple from a fluorescent tube – which can be a source of interference to the sensor in normal use. Makes also vary in their spectral response – something to consider when you compare the brightness of different coloured fabrics. Curiously, some respond well to infra-red and can pick up the signal from a remote control. Variously calibrated as %, Watt/m² or lux.

Uses for a light sensor

• Monitoring of light levels day/night. Light levels in photosynthesis.
• Environmental studies.
• Response of a flash gun using a fast data logger.
• As a timing light gate – e.g. to time the swing of a pendulum.
• Variation of light intensity with distance: the inverse square law.
• Colorimetry in the starch-iodine reaction. Rate of reaction between Iodine and propanone.
• Turbidimetry of acid and thiosulfate reaction, action of pepsin on milk, of trypsin on milk or of the proteases in biological washing powders.
• Investigating diffraction and interference patterns.
• Measuring leaf transparency.

Light sensor notes:
Light sensors have logarithmic or linear ranges. The LOG setting will sense the full range of light intensity. This would be useful in monitoring sunshine. The logarithmic type is a bit less suitable for quantitative work. It is however, much simpler to use.

Diode types of light sensor can respond much faster than light dependant resistor types. The slower type will respond less to interference such as fluorescent strip lighting. The fast type can pick up AC ripple.

I’ve rated these sensors but your assessment will be different. I give a score, out of five, for the sensor’s intrigue, interest, and learning potential. I also give a score for how often a science department might use it.

colorimeter sensor 

Rare but very useful for quantitative work in biology and chemistry experiments where a rate of a reaction is measured. Bleaching food dye, the iodine-propanone reaction and the action of pepsin on milk are some examples. Monochromatic light is very important in colorimetry, so this ‘sensor’ will come with a few filters. Main advantage is one of convenience over making your own colorimeter with a light probe.

chemistry uses: bleaching; iodine-propanone reaction; thiosulphate-acid reaction.
biology uses: starch-iodine- amylase reaction; action of pepsin on milk; action of trypsin on milk; or action of the proteases in biological washing powders.

infrared sensor

Might be used for measuring radiant heat or the heat from different surfaces. There are still too few reports of curriculum applications where infrared changes in relation to time or some other variable. However there ought to be lots of uses to measure heat loss / heat flow but we never did them because the sensor was rare. My rating was ** / +