Author: Eng. Sandro Costo
To better understand the differences between lighting systems, let's start with the glossary.
Potential difference
The term potential difference refers to a quantity, measured in volts (V), that represents the difference between a point at a certain electrical potential and another reference point. This quantity is called voltage. Taking, for example, a battery like the small square ones we've all used at least once in our portable radio, alarm clock, or other device, we can read on its casing that it is a 9-volt battery. This means that the battery is capable of creating a potential difference, or voltage, across its electrodes (+ and -) equal to precisely 9 volts.
Electric current
Electric current (I) is the flow of current through a conductor per unit of time. It is measured in amperes (A).
Electric power
Electrical power is a composite quantity of the two previous quantities and is measured in Watts (W). The formula for calculating power from potential and current is as follows:
W=V*I
Power is derived from the work done during a unit of time. The unit of work is the Joule and the unit of power is the Watt: 1 Joule per second corresponds to 1 Watt (W = J/s).
La luce
| Appointments | English term | Unit | ||
| Amount of light | amount of energy emitted, received or transported by radiation |
lumen second | lm s | |
| Luminous flux | Luminous flux | amount of light energy emitted by a source in the unit of time |
lumen | lm (= cd sr) |
| Illuminance | Illuminance | incident luminous flux per unit of surface |
luxury | lx (= lm/m2) |
| light intensity | Luminous intensity | luminous flux emitted per angle unitary solid |
candle | cd |
As you can see the lumens are linked to the power of the bulb (Watt) but the illuminance (Lux) is given by
lm/m^2 and for this reason torches with different parabolas will give different illumination levels for the same power: therefore a 100 W bulb with an 8° parabola will have a much more compact, bright and penetrating beam than one with a 100° parabola which, however, will illuminate a much wider area, fig. 1.
Types of light bulbs
Underwater torches are mainly divided into three main types:
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Halogen
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LED
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HID
1. Halogen
Definition: any glass bulb that has a filament inside (typically tungsten or similar) and that emits light according to the principle of incandescence (the principle by which fire develops) by applying a voltage directly to the poles.
Halogen bulbs, if you prefer, are ALWAYS built with an internal filament that progressively wears out: no matter how long the bulb is turned on, the filament becomes incandescent (i.e., it emits light), and as it does so, more and more tungsten atoms detach from it, until, once it becomes too thin, it breaks and stops the incandescence process (i.e., the bulb burns out). From this, it's obvious that it's only a matter of time. Factors such as time and conditions of use, or the quality of the bulb's construction, often determine the bulb's lifespan. The same bulb, therefore, can last from a trivial amount of time to an infinite amount of time. To slow down this filament wear process over time, it has been discovered that filling the halogen bulb with gases such as xenon slightly extends its lifespan. Atoms evaporate from the tungsten filament and combine with halogen atoms, forming a gaseous compound that falls back onto the incandescent filament, redepositing the tungsten atoms. The halogen atoms are then free to recombine with the tungsten atoms. This cycle, called regeneration, is the secret to the long life of this particular type of incandescent lamp.
Halogen lamps are certainly the most common ones available on the market; they come in a wide variety of types and wattages. Generally speaking, for recreational/advanced diving without any special needs, 50 W with a burn time of 50/60 minutes is sufficient; obviously, 100 W is better, but increasing the wattage reduces the burn time or increases the cost of larger batteries. Xenon bulbs are often used in halogens, which produce a much whiter light (around 3500 K).
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2. LED lamps
The term "LED" is an acronym for "Light Emitting Diode." LEDs consist of a PN junction made of gallium arsenide or gallium phosphide, both materials capable of emitting light when passed through an electric current; the value of this current is between 10 and 30 mA.
The operation of the LED is based on the phenomenon called “electroluminescence”, due to the emission of photons (in the visible or infrared band) produced by the recombination of electrons and holes, when the junction is polarized in the forward direction.
LEDs have a positive and a negative terminal, and to function, they must be connected to a circuit with this polarity in mind. The positive terminal is usually the longest, but you can identify it with certainty by holding the inside of the LED up to the light: as you can see in the figure, the positive electrode is thin and spear-shaped, while the negative electrode resembles a small flag.
When using an LED, it is always necessary to place a resistor in series with it, in order to limit the current flowing through it and prevent it from destroying itself; the voltage drop across an LED can vary from 1,1 to 1,6 V, depending on the wavelength of the radiation emitted (shorter wavelengths correspond to a higher voltage drop).
LED lamps have two major advantages: battery life and shock resistance. This certainly makes them a very advantageous solution for backup lighting and for situations where long battery life is required, such as in caves. During daytime dives, however, they don't offer the same performance as halogen lamps.
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The following table provides some clarifications on how LEDs work.
| questions | Response | |
| 1 | LEDs do not generate heat | LEDs generate heat, but retain it in their internal, so it is necessary that the cables or the casing can dissipate it. If it is not designed correctly, the LED will have a very short duration. |
| 2 | LEDs do not produce enough light for general lighting applications |
High-power LEDs emit enough light to many special and general lighting applications. |
| 3 | The white light of LEDs does not have a quality sufficient to replace incandescent lamps |
Most white LEDs emit a bright light with a color temperature of 5500K. Very few are capable of offer a color temperature that reproduces that of lamps incandescent. |
| 4 | The CRI of LEDs is not sufficient for lighting applications |
Typically white LEDs have a rendering index of color of 60-70, both at 3200K and 5500K. |
| 5 | High-power LEDs are expensive | Considering the lumen/$ ratio, high-power LEDs power can be the most convenient among those available on the market. |
| 6 | LEDs are energy efficient better than any other light source |
White LEDs are about twice as efficient of incandescent lamps. Given its directional nature, the light emitted by an LED is more easily controlled, allowing for a superior efficiency general lighting. |
| 7 | The chromatic discontinuity of the LED white is too large to be used in applications general lighting. |
Given the manufacturing characteristics of the LED white it is possible to produce a range of colors. During the lighting design and production must be carried out attention to managing the chromatic distribution to produce a quality solution. |
| 8 | It is too complex to make a LED lighting solution |
Similar to other lighting technologies, such as fluorescent lamps and high-efficiency fluorescent lamps intensity (HID), LEDs require drive circuits and optical and thermal elements suitable for offering all their advantages. |
| 9 | All LEDs have a lifespan of 100.000 gold |
It has been shown that some LEDs, depending on the color and brand, maintain the amount of usable light or significant - about 70% of the light originally emitted - for 6.000 hours or less. |
| 10 | The accessories suitable for use with the LEDs, such as optical or thermal components and electronic drivers, do not are available in sufficient quantity |
There are currently hundreds of manufacturers who offer components for LED systems. |
3. HID lamps
(High Intensity Discharge)
These are light bulbs without a metal filament. Two electrodes immersed in a xenon atmosphere are connected to the two poles of the electrical circuit. The electron discharge between the two produces a very intense light, about twice that of halogen lamps, and extremely white (so much so that it even appears blue). Because they lack a filament, these bulbs last longer than conventional ones (still about twice as long) and consume 70% less energy. They must be regulated by an electronic control unit to prevent damage from voltage fluctuations.
HID bulbs are much more efficient than halogen and Xenophot lamps; their light output is also very high: a 35W HID with 3500 lumens is equal to 100 lm/W, while for non-boosted halogens (which last around 2000 hours) we are around 25 lumens/watt; boosted halogens, on the other hand (they last around 50 hours and many underwater lamps work this way) are around 35 lumens per watt.
It can be deduced that as a first approximation, HIDs have a performance 4 times higher and therefore, with the same battery, allow for quadruple the autonomy.
On the other hand, HIDs have some disadvantages: first and foremost, the cost, as the bulb alone can cost more than 100 euros! The electronic control unit costs around 200 euros. Sure, you save on the battery, but the voltages involved are in the range of 6000-30000 volts, and therefore, everything is extremely sensitive to humidity: even a tiny amount of condensed water generates arcs that cause irreparable damage to the electronics, resulting in significant financial losses.
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