Measuring Light
Yes, indeed you can. Whilst it may seem impossible because we can't physically touch it, light is in fact measurable just like the temperature of a room. Though we would use the term light intensity. If you're one that ever seen a photoshoot go on, you'll see that before the button is pressed to take the winning shot, this little doo hickey appears
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This little contraption is where the magic happens and is called a light meter
A light meter has the ability to determine the proper exposure for a photograph, and determines whether a room is too bright or dim for a specific requirement for a photo and measures the intensity of light. Also called illuminance
Illuminance: The luminous flux per unit area at any point on a surface exposed to incident light. It is measured in luxes.
Exposure: the amount of light per unit area reaching a electronic image sensor (or film), as determined by shutter speed, lens aperture and scene luminance
Sensing there may be some confusion, we may need to step back and define a few more terms.
Lux: lux is the unit of measurement for light intensity. One lux is equivalent to the light level of a single candle light. The symbol for Lux is lx
Hoping that a few definition terms are all cleared up. Let's continue.
Whilst taking photos and using a light meter to measure the illuminance, certain numbers must be kept in might. Found below are examples of the amount of light intensity in various situations.
| Condition | Illumination | |
|---|---|---|
| (ftcd) | (lux) | |
| Sunlight | 10000 | 107527 |
| Full Daylight | 1000 | 10752 |
| Overcast Day | 100 | 1075 |
| Very Dark Day | 10 | 107 |
| Twilight | 1 | 10.8 |
| Deep Twilight | 0.1 | 1.08 |
| Full Moon | 0.01 | 0.108 |
| Quarter Moon | 0.001 | 0.0108 |
| Starlight | 0.0001 | 0.0011 |
| Overcast Night | 0.00001 | 0.0001 |
| Activity | Illumination (lux, lumen/m2) |
|---|---|
| Public areas with dark surroundings | 20 - 50 |
| Simple orientation for short visits | 50 - 100 |
| Working areas where visual tasks are only occasionally performed | 100 - 150 |
| Warehouses, Homes, Theaters, Archives | 150 |
| Easy Office Work, Classes | 250 |
| Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories | 500 |
| Supermarkets, Mechanical Workshops, Office Landscapes | 750 |
| Normal Drawing Work, Detailed Mechanical Workshops, Operation Theaters | 1,000 |
| Detailed Drawing Work, Very Detailed Mechanical Works | 1500 - 2000 |
| Performance of visual tasks of low contrast and very small size for prolonged periods of time | 2000 - 5000 |
| Performance of very prolonged and exacting visual tasks | 5000 - 10000 |
| Performance of very special visual tasks of extremely low contrast and small size | 10000 - 20000 |
You may wonder, well how on earth would I know all that? Math. There is math in everything and you can calculate it. Though we won't get into that right now.
Now you may wonder, great. I understand the terminology but how does this all come together?
- Set your camera to manual mode, in order to set up the ISO settings and aperture settings ( F Settings)
ISO: measures the sensitivity of the image sensor towards light in how much light is let through, The higher the ISO, the more sensitivity to light. Most of the time, lower ISO settings produce clearer pictures whilst a higher ISO will cause graininess
Aperture : The aperture setting changes the size of the lens, and therefore how much light the camera lets in. This setting is describes using the unit f/stops. A larger aperture number, like f/11, means a smaller lens size, and a smaller number, like f/1.4, means a larger lens size. Aperture affects your photos' depth of field and shutter speed
2. Input the ISO number and aperture into the light meter. Replicate the settings on your camera into the light meter.
3. Turn on the light sensor
4. Set your light meter to the appropriate mode . Depending on whether you will use flash or not
5. Aim the light meter towards the subject that you are taking a photo of. Then press the button on the light meter.
Once the measurement is done by the light meter, it will give you the appropriate ISO and Aperture settings in order to capture a picture in the given lighting setup.