Bulbs vs LEDS

BULBS

Miniature bulbs work in the same way as full-size traditional light bulbs, whereby a fine wire filament is wrapped in a coil within a glass bulb. When electricity is passed through the filament, it glows brightly and generates heat. The main drawbacks of these bulbs are their limited lifespan and the fact that they inevitably run ‘hot’, which is not desirable in close proximity to materials like card, paper or soft plastics. They can be rather delicate and also demand a fair amount of ‘juice’ to keep them illuminated, especially when a number of them are in use. Often referred to as ‘grain of wheat’ bulbs, miniature lamps are very cheap and available in various colours and sizes; typical bulb dimensions are 3mm wide by 6mm long. They’re incredibly easy to use and can be powered by anything from 1-12V AC or DC, via batteries or a mains transformer. The higher the voltage, the brighter the bulbs will shine, which allows the levels of light to be tailored, either by adjusting the power supply, adding a resistor to the circuit or by wiring the bulbs in series rather than parallel (see diagram next page).

LEDS

LEDS, or Light Emitting Diodes to give them their full title, work in a very different way to traditional bulbs and, in most cases, require a DC power supply. There’s no delicate wire filament or glass bulb, as the tiny diodes emit light as electrical energy passes through, although the power can only flow in one direction, from the anode to the cathode. All LEDS are supplied with one lead shorter than the other. The longer is the anode and the shorter the cathode. The positive polarity from the power supply must only be applied to the anode, via a resistor. The value of the resistor depends on the rating of the LED and the power source and can be calculated using Ohm’s Law (see panel). To make life easier, a number of model railway lighting products that contain LEDS come supplied with a pre-wired circuit board, some of which may incorporate an AC-DC converter, along with all of the necessary resistors installed. A good example is the range of pre-assembled station and street lamp sets from Dccconcepts, which include both filament bulbs and LEDS. The circuitry supplied allows the lamps to be powered by anything from 9V to 18V AC or DC. Another example is Woodland Scenics’ modular Just Plug system, consisting of a central light ‘hub’, into which pre-wired LEDS can simply be plugged. Mains or battery power options are available, taking away any need for soldering or faffing around with separate components and cables. Such convenience comes at a cost, however, and creating your own circuits from lamps or LEDS is far cheaper. Never connect LEDS directly to a battery or other power source, unless instructed otherwise by a product’s instructions, or the LED may be damaged. Some LEDS now feature built-in resistors, but this should be double-checked in the instructions before use. LEDS offer the advantage of shining to a uniform brightness, regardless of power fluctuations, hence why they’re popular in model locomotive lighting circuits, especially for non-dcc control. Depending on the shape of the LED, the light may be emitted in a more focused direction, in contrast to the radiating glow of a filament bulb. Choice of coloured LEDS used to be limited, but in recent times a wider range of colours has become available, from bright white (perfect for modern industrial lighting) to red, yellow and green. The cost has also decreased significantly, making LEDS much more affordable.

Traditional bulbs emit a pleasing, ‘warm’ light that radiates naturally. By lowering the input voltage, the bulbs can be dimmed.

Miniature grain of wheat bulbs are a cheap and easy lighting option, connecting simply to a battery or low-voltage power supply.

Right: Filament bulbs generate heat while illuminated, so they must be sited with care. Ensure plenty of space around the bulb and some means of ventilation. Secure the cables with a blob of epoxy glue or insulation tape.

Modeller-friendly lighting sets, such as these lamps from Dccconcepts, include all the necessary circuitry to make LEDS compatible with a wider range of power sources. All you need to do is connect the wires to screw terminals.

Above: Hornby’s Skale Lighting system removes the need for any soldering or joining of wires, providing plug-in light bulbs, sockets and cable. All that’s required is a suitable power source.

Above: LEDS come in various shapes and sizes. Those with leads sport one longer than the other to denote the anode (longer) and cathode. Inset: Most LEDS emit light in a more focused direction, in contrast to a traditional bulb’s general radiance.