Lighting completes the trio of topics I did not want to think too much about, but unlike plumbing and electricity, I’ve found it difficult to kindle any particular enthusiasm for it. After a handful of false starts, I have decided that I need to cut to the chase with this one, to the one aspect that has perked any interest: Radial Circuits. It came to my attention by means of one very helpful and well-informed John Ward. (Here is his YouTube channel for all sorts of electrical explorations). I did grudgingly dedicate a Google-search session to the humble lightbulb itself. So before we get to the fun, here is the hum-drum.
The role of the lightbulb is to convert energy into light energy. The traditional light bulb, or rather an Incandescent lightbulb, was the first of its kind and it hasn’t changed greatly since it was invented in the late 1800’s.
The glass bulb is capped with a metal base. This base has two metal contact points which connect to the tungsten filament (a very thin coil of metal wire with an incredibly high melting point). When the light bulb is connected to an electrical current, the electrons in the copper collide into the atoms in the filament causing them to vibrate. This vibration heats the atoms to approximately 2000+ degrees Celsius, causing them to glow and thus giving us light. The filament is sealed in a glass bulb to keep oxygen away from the wire as without this seal, the tungsten would burn up within a couple of minutes.
[This video captures the mesmerising manufacturing process. Seriously, treat yourself. It is super satisfying].
Though immensely popular, incandescent light bulbs are incredibly inefficient; approximately 90% of the energy consumed by the incandescent bulb is used to heat the filament alone. That means only 10% is used to create light, the sole purpose of a lightbulb in the first place. This considerable flaw has seen the development of a number of other light bulb designs, each with the goal of higher efficiency.
These are very similar to Incandescents except that the bulbs are filled with the gas Hydrogen Bromide. This gas captures and returns any stray, evaporated tungsten atoms, prolonging the life of the filament. It also keeps the glass clear.
Glass tubes are filled with gas and capped at each end with an electrode (electrical conductor). When connected to an electric current, electrons knock into the mercury atoms in the gas. This excites them into emitting both visible and ultraviolet light. The insides of the tubes are coated white so that the ultraviolet light can be absorbed and remitted as visible light. This also prevents us from being exposed to UV rays.
Light Emitting Diodes (LED)
Before we launch into LEDs I will note that I spent far too long researching diodes and how they work, especially considering I had set out to avoid longwinded research into lighting in the first place. Worse, I still don’t believe I truly understand how they work- despite struggling through numerous long-winded YouTube videos. That said, I need proof that I did something with my morning, so I have included it anyway. Please feel free to skip the next three paragraphs because to accept the diode as a light emitting chip is most likely more than sufficient.
A diode is a semiconducting electronic device that has two terminals, one negatively charged (cathode), the other positively charged (anode). It has low resistance in one direction, and high resistance in the other, meaning it will only allow electricity to flow in the one direction.
Semiconductors are materials that are typically insulators; meaning they don’t encourage the flow of electricity. They can, however, be turned into conductors through a chemical process called doping. Extra element atoms can be added to a semiconductor material like Silicon, giving it additional electrons. Materials altered in such a way are known as N-type (negative type) and carry a negative electric charge.
Similarly, you can add atoms which take away electrons, leaving ‘holes.’ When this occurs, the material becomes P-Type (positive type.) These holes carry a positive electric charge. Diodes are created when an N-Type and a P-Type are paired together.
The border between the P-Type and N-Type is known as the P-N junction and it is this that keeps the two sides separate. Without an electrical charge, only the electrons and the holes in the center can recombine. This creates a depletion zone where there are no free carriers. It also creates an electrical field. Only when the diode is connected to a battery voltage higher than the electric field can the N-Type electrons gain enough energy to cross the junction. This shrinks the depletion zone and allows the electrons to fill the holes of the P-Type, creating light (photons). The key thing to note is that the battery must be connected negative to negative/positive to positive, otherwise the depletion zone grows larger and there will be no light.
In conclusion, diodes in LEDs create light. They are an incredibly efficient way of doing so, using only 10% of the energy used to illuminate an incandescent bulb. The diode itself only amounts to a very small semiconductor chip, known as the ‘die’. These can be cased inside tiny bulbs or mounted directly onto surfaces.
What are the different LED chips available?
LED DIP (Dual In Line): This is the traditional LED light with a tiny bulb (capsule shape top). The hard plastic (epoxy) cap encases a DIP chip and has two parallel connecting pins which act as the anode (longer leg) and cathode. They produce approximately 4 lumens per LED.
Surface Mount LEDs: Smaller and more efficient than the Dual In Lines, SMD’s can produce 50 to 100 lumens per watt. The chips are welded onto circuit boards and used across numerous applications (lamps/signage/car lights/computer monitors). SMD chips can have more than two contact points and up to 3 diodes, each with an individual circuit. This means a red, blue and green diode can be used, allowing the creation of almost any colour.
Chip on Board LEDs: COB’s are the newest application of LED chips and allow for 9 diodes or more. They cannot change colour like SMDs but can produce more lumens with less energy so are used for floodlights. It produces a minimum of 80 lumens per watt.
Evidently, discussion of watts and lumens demands a post of their own, but for today I am so very done. Plus, Harry and Meghan’s wedding is about to screen! Priorities!