portable continuous lighting for still and video photography

Now that we are getting video capability with our dSLRs, it’s time to think about using portable continuous lights as an alternative to flash – not only will it work for both still and video photography, but you get to see exactly the effect of the lighting making it MUCH EASIER to light your subject than with flash.

This is a rapidly changing aspect of the industry with new or improving light technologies coming out all the time – particularly “cool lights” such as fluorescent, HMI/HID and LED-based lights.

Choice of light will be determined by your requirements, and considerations need to include:

  • how much light do you need? is it just as fill in in low light situations and thus low output will suffice? do you wish to fill in sunlit faces in which case much higher output is needed?
  • what colour temperature – daylight vs tungsten? can you change it?
  • can you adjust the intensity of the light output?
  • what is the quality of the light? is it an evenly illuminated beam? can it be focused?
  • what is the beam coverage? will it cover 16:9 image aspect ratio?
  • are you happy to accept a hot light source which can make it difficult to hold and may burn?
  • how long can you use it for with built-in or portable battery?
  • what connectors for DC power supplies – 4 pin XLR?
  • how big and heavy is it?
  • does it have a strong hot shoe mount or a tripod mount, or a studio light stand mount?
  • can it take accessories such as barn doors, filters or perhaps even a softbox?
  • can you afford it?
  • can you replace the bulbs and how long do they last?
  • do you need to take it underwater? – see sartek, HDVseatek and bhphotovideo’s catalogue
  • do you need infrared light as well – such as for Sony nightshot mode?

Lighting technology options:

  • tungsten
    • generally cheapest but hot lights which use the most power for given light output
    • an option if you are mainly using it to mix with other indoor tungsten lighting, and you have access to AC power – not so great for DC portable use and globes tend to blow more frequently as they have a short life
    • ~10 lumen per watt power consumed
  • quartz halogen
    • traditional camcorder video lights as they have high output, but do consume battery power quickly
    • lamps become hot and globes have more limited life spans
    • 10-16 lumen per watt power consumed
    • tungsten colour temperature of 3200K which tends to shift with age
    • some have a dichroic filter to change the colour temperature of the tungsten halogen light output to match daylight
    • bulb life span 60-100 hours
    • examples:
  • fluorescent
    • an increasingly popular lighting option now that higher output, flicker-free with daylight colour temperature options are becoming available
    • globes tens to have 10,000 hour life span
    • 35-50 lumen per watt power used
  • HMI HID mercury vapor, metal hydride bulb
    • tend to be more expensive and require electronic ballasts but new versions are becoming more compact with built-in computer-controlled high frequency ballasts for flicker-free video
    • generally have coated bulbs to reduce the harsh light output
    • 5 times more light output per watt than quartz halogen
    • HID lights give 85-108 lumen output per watt power used
    • daylight versions generally are 5200-5300K, while underwater versions tend to be 6000K
    • wikipedia – Hydrargyrum medium-arc iodide, or HMI(R) – HMI is a trademark of OSRAM GmbH
    • HID = High Intensity Discharge
    • create light using a tiny ball of superheated, electrically-charged plasma inside a small quartz bulb and provides more spectral content than LED
    • examples:
      • 10W 12V 1000 hour Frezzi HMI Micro Sun Gun which gives same output as their 35W halogen model of 270 lux at 5 feet with diffused front glass, which according to my calculations, gives ~600 lumen or 600 lux at 1m – but to get this output for daylight corrected halogen using a dichroic filter, you would need a 50W halogen lamp. The 12V 2.3Ah battery provides 2 hours power for this light and you can get adapters for other batteries including XLR-4 adapters.
      • videolighting.com’s HMI studio lights which are powerful enough to be used with studio soft boxes as they use 150W (800W tungsten output) 5200K globes which have 7000 hour life span with option of 3 globe light heads for more power.
  • LED
    • quickly becoming the most popular video light source when portability and low power consumption is a priority
    • for a better understanding of LEDs see ledmuseum’s tests and from this info, I interpret the data to suggest that:
      • there are 2 basic LEDs – traditional red/yellow (usually based on gallium arsenide phosphide and usually require ~2.4V) and super bright blue (invented in mid-1990s by Nichia and usually based on gallium indium nitride, and when a phosphor coating is added, they become our super bright white LEDs and usually require 3.6-3.8V)
      • the light output is markedly decreased if the LED is designed for a wider beam angle
      • individual LED output is usually measured in millicandela and this can be converted to lumen by taking into account the beam angle (see below)
    • examples:
      • 60 LED rechargeable units which can be attached to each other to form a bank of lights, all mounted on a single hot shoe
      • 600 lumen Lumiere L60182
      • Toshiba’s AL-LED-FS-6 studio spotlight giving 860 lux at 3m with 2m diameter spot at 5500K running at 100W power and gives equivalent of a 500W halogen but without the IR output (which makes subjects hot) and without UV output (which fades materials), and which lasts 20,000 hours instead of 300 hours. It weighs 7kg and operates on 100V AC power and costs ~$US5,000

Measuring light output:

  • lumen (lm) is a measure of luminous flux (visible light) of a light source and equates to 1 candela (cd or 1 candle) if the source emits a beam covering ~65deg. A 1 candela source which emits in 360deg equally, gives 4π lumens = 12.6 lumens.
    • tungsten/halogen lamps give ~10-17 lumen per watt – a 100W standard light bulb gives ~120 candela = 1,700 lumen in USA and 1,300 lumen in 220V regions
    • flourescent lamps give 35-50 lumen per watt, however, new LED fluorescent lamps give 100lm/W
    • HID lamps give 85-105 lumen per watt
    • white LED lamps give 80-100 lumen per watt (rising from 30lm/W in the early 2000′s and expected to be 150lm/W by 2012) – a 2V, 19mA white LED with a 30deg beam angle and rated at 7530 mcd equates to 1.6 lumen output per LED (see converter here)
  • lux is a measure of the amount of light illuminating a surface, thus this will depend on the output of the light source (lumen) and distance to the surface (eg. meters) and the angle of incidence on the surface
    • for a point source, lux = (I/s^2)cos a, where I = lumen, s = distance in meters, a = angle of incidence
    • thus 1 lumen light source hitting a perpendicular surface placed 1 meter away will give 1 lux illumination and illuminance follows the inverse-square law for distance
    • One footcandle ≈ 10.764 lux
    • examples of illumination on typical surfaces are:
      • family living room ~ 50 lux
      • very dark overcast day ~ 100 lux
      • office lighting 320-500 lux ≈ 1/50th sec, f/5.6 at ISO 800 (almost the limit of the GH-1 using the 14-140mm HD lens – although you can go to ISO 1600, and even down to 1/2 sec in full manual mode)
      • sunrise or sunset on a clear day ~400 lux
      • overcast day or typical TV studio lighting ~ 1,000 lux
      • full daylight (ie. illumination from blue sky) but not direct sun ~10,000-25,000 lux
      • direct sunlight 32,000-130,000 lux
    • it should be obvious from the above that most portable continuous light sources are going to have a hard time competing with direct sunlight, although the more powerful ones, when close to the subject will assist with filling in shadows in this situation

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