Introduction to tungstènes and hmi

Introduction aux tungstènes et aux hmi

The security is the master word in lighting.

When current flows through a body, muscles (flexors/extensors) are activated involuntarily. Two cases are possible :

  • Or we get project, with an additional risk of damage related to the fall ;
  • We are tétanise and the support received increases strongly.

In both cases, the ONLY reflex to adopt is to cut the general power supply as soon as possible.

NB : the people in tetany cannot shout.

Here’s a definition to start :

COLOR TEMPERATURE : expressed in degrees Kelvin (K), it determines the color of the light. The higher the temperature, the more the light will be blue. A contrario, the more it will be weak, the more it will be red. The day light is around 5600K.

Define this large family of lamps :

  1. Filament lamps (commonly referred to as tungstènes “) : 3200K ;
  2. Lamps HMI (commonly referred to as daylight “) : 5600K ;
  3. Lamps fluoride.
LAMPS HAS FILAMENT LAMPS HMI LAMPS HAS FLUORIDE
BENEFITS
  • Flexibility
  • Low-cost rental
  • Color temperature reliable
  • Light output
  • Mix with the light of the day
  • Low heat emission
  • Ideal to recreate the atmosphere of the streets of night
  • Large illuminated surface
DISADVANTAGES
  • Major heat
  • Significant consumption of current
  • Not usable in daylight
  • Color temperature approximate
  • Cost rental high
  • Low-power

Filament lamps

In common language, we speak of a lamp to the tungsten T.

In reality, modern lamps are of the type TH (Tungsten-Halogen). Because at equal power, the TH emit considerably less heat than T. significant Advantage for the comfort of the teams.

The TH (and T) do not mix without loss of effectiveness in the light of the day. They are heavily used in the interior, that is to say, in the studio or for the stage.

Their flexibility is important because they are directly connected to the mains. This is not the case of lamps of type HMI who need a ballast*.

The HT and T are democratized, which translates into a low cost rental.

Their color temperature is easily measurable and correctable.

The lamps HMI

We spoke above of a lack of flexibility of this type of lighting, which is inherent in the ballast. The latter serves as a leader to turn on the projector, that is to say, form the arc. Therefore, it is necessary to connect the projector to the ballast and the ballast to the sector.

We can, however, qualify this disadvantage by specifying that the light output of a lamp type HMI is four times higher than that of the TH. In fact, the light released (expressed in lumens) by the HMI changes as a function of the power supply (W).

If the HMI is increasingly being used, this is mainly for two reasons :

Firstly, thanks to film (and now sensors) is always more sensitive, the filming in the external environment are increasing continuously.

Secondly, it is impossible to mix the light of day and the light the tungsten without loss of power or filtering effects. The main flaw of the HMI is that the color temperature is approximate and can vary greatly from one lamp to another.

The lamps fluoride

Let’s just say that the lamps are composed of rare gases and need a ballast. They are especially used at night to reshape public lighting, which is not satisfactory or which does not correspond to the expectations of the DP (Director of Photography).

 

We will detail in the next section the operation modes of each lamp, as well as the families

* The term ballast refers to any electrical component used to reduce the current in an electrical circuit. A ballast may take the form of a simple series resistance as for the fluorescent tubes, low power. For the applications of high-power, the energy dissipated in the resistor ballast would be too large. It then uses capacitors, coils, or both at the same time. The advantage of these components compared to a resistance is that, ideally, their impedance does not include the term resistive and does not, therefore, losses by Joule effect. (reference : fr.wikipedia.org)

 

Thibault Taccone

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