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Light 'n' effect
For our latest diverTest Extra, John Bantin has taken 24 mid-range lamps in the £100-£300 price bracket to see how they compare.
Which ones shone in his test? |
How did they perform? | Comparison Table
in the dark, almost any working lamp is better than none. Our eyes automatically adjust for brightness.
However, once you dive alongside someone with a better lamp, you may discover that yours is not very bright, or that its beam is patchy. Choosing a lamp can be difficult, because you rarely get a chance to compare them side by side in controlled conditions. So we have done that for you.
Here are 13 questions to ask when choosing which lamp to buy, and which we set out to answer in this comparison test:
Some lamps use conventional tungsten bulbs, while others have halogen-filled (xenon) bulbs that can burn for longer at a higher temperature or light output.
Others use expensive HID (high intensity discharge) bulbs. Watt for watt, these produce far more light than a conventional bulb and at a higher colour temperature.
The disadvantage is that they should be switched on and left to warm up before switching off again. Ignoring this rule reduces the life of the expensive bulb and ballast. Some of the latest lamps use high-output LEDs (light-emitting diodes).
These consume little power, resulting in lengthy burntimes. The light is quite cool (blue), though not exceptionally bright. Some of these lamps use a cluster of LEDs, each with its own reflector, to produce a brighter light.
Our eyes adjust for the colour of ambient light, so we feel as comfortable in warm (low colour temperature) domestic lighting as we do in daylight.
We took a typical tungsten lamp as our standard white, and you will notice that HID- and LED-based lamps give a much colder (more blue in the shadows) and less kind light, though it penetrates blue water better.
The term "watts" (watts = volts x amps) represents electric current consumed. People use wattage to compare a light's brightness, but in fact it is almost irrelevant. It's the amount of light that arrives at the subject that counts, and that involves the brightness of the bulb combined with the efficiency of the lamp's reflector. Brightness is measured in lumens.
We measured the brightest part of the beam over 1.35 metres (lamp submerged), using a highly sensitive scientific lightmeter in a submersible housing. Figures in lumens mean nothing unless you compare the lamps side by side in identical conditions, which is what we did.
If a hypothetical least-bright lamp had a brightness factor of one, the figure for each of the other lamps denoted how many times brighter they were.
To compare two lamps, for example the JMD 5060 (brightness factor 24) and the Beuchat (brightness factor 32), the beam of the Beuchat was 32/24 = 1.3 times as bright). Brightness should be considered alongside the quality of the beam.
We photographed each beam from a set position of both camera and lamp. The photographs reveal exactly the size and shape of the beam thrown by each lamp. Some produce a very narrow beam, while that of others is very wide. Some beams were even, whereas others were patchy.
The camera automatically adjusted its exposure to suit the brightness. The photographs inform you about beam shape - not about how much light there was.
We used the manufacturers' claimed figures, which prove reliable when batteries are new. A long burntime can mean that a lamp will work for several dives, uninterrupted by battery changes or charging. A short burntime might mean that you get left in the dark while you are still in the water.
Some lamps give the user the option to use them at less than maximum light output, giving a longer burntime. The better LED lamps tend to reduce their output in steps automatically as the battery charge is depleted. The burntime at the brightest output is usually about a third of that stated overall.
By and large, alkaline cells give a longer burntime than a rechargeable nickel-metal-hydride or nickel-cadmium battery, but the latter often produce a brighter light. Remember that most alkaline batteries can now be substituted for ni-mh batteries of the same size.
Ni-mh batteries can be recharged at any state of charge, whereas it is better to run a ni-cad flat before recharging it. However, the memory effect often attributed to ni-cads recharged when not fully depleted is often over-stated. Lithium batteries pack a punch for their size but are priced accordingly.
Using the manufacturer's suggested time, each lamp was charged to the maximum before measuring light output. A short charging time is convenient if the window of opportunity for recharging is likely to be short. This applies where mains electricity supplies are unreliable or intermittent, such as on boats, or where a small generator is used.
We weighed each lamp in the air and then submerged in fresh water. Dry weight can be important when paying airline excess-baggage charges, and too much inwater weight can affect your buoyancy.
Some lamps are made of plastic, others of anodised aluminium. Some have glass (borosilicate) fronts while others use plastics lenses. The latter should not be turned on unless submerged in cooling water.
On some lamps you simply rotate the front lamp assembly so that it bears down on the battery to make a contact. Avoid switching off while under water in case you undo it too much and cause a flood. Some lamps have a lock on the switch to avoid accidental switching-on and a depleted battery or, worse, a fire in your luggage. Airlines now insist that batteries are disconnected from lamps in transit.
A lamp that must be opened to charge or replace batteries is more vulnerable than one that does not. Seals are protected by O-rings, and the more openings protected by user-serviceable O-rings there are, the greater the opportunity for water to enter.
The lamps compared here represent a mid-price range from £99 to £300 recommended retail price.
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| Beaver | Beaver Sports | 01484 512354 |
| Beuchat | Alpha Distribution | 01709 515157 |
| Fa + Mi | Submerge | 01484 711113 |
| Greenforce | Lumb Bros | 0161 6815790 |
| Halcyon | Silent Planet | 01305 862220 |
| JMD | JMD Technology | 01751 476972 |
| Kowalski | Lighthouse Diving | 01599 577277 |
| Seac Sub | Beaver Sports | 01484 512354 |
| Tektite | Lumb Bros | 0161 6815790 |
| TrebleLight | Snooba | www.treble-light.co.uk |
| Underwater Kinetics | Sea & Sea | 01803 663012 |
How did they perform? | Comparison Table
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