LEDs

Seeing the light at Redemption Roasters

Coffee Bloomsbury

Redemption Roasters Cafe on Lamb’s Conduit St.

At the top end of Lamb’s Conduit Street there is an unassuming café in a fairly modern building at the corner of Long Yard. In recent weeks I had been hearing a lot about Redemption Roasters and their café. First came the review by Double Skinny Macchiato, then various comments on Twitter, in Caffeine magazine and finally, an article in the FT. In an ideal world, it seems to me that cafés can act as seeds towards forming a better society. Local and independent, a friendly place where you can chat with the baristas (or café owners), and so where communities can form and develop. All that I had heard about Redemption Roasters café fitted, in some way, into this ideal which meant that it was not going to be long before I headed towards Bloomsbury and tried this new café.

Plenty of seating could be found inside the café, with tables of two or four and benches around the space. The counter was immediately in front of us as we went through the door and the friendly barista took our order (long black and soya hot chocolate, what else?) while we took our seats. There were a fair few staff in the café when we visited, so many in fact that we weren’t initially sure who were staff and who were customers. Nonetheless, their joviality transformed the café’s fairly austere decor more into the feel of the welcoming space of a living room.

blue shadow, hot chocolate

A layered hot chocolate? No, just the reflection of the saucer in the glass.

Having taken our seats and started to look around, we found that much could be said about the science in this café. From the SMEG refrigerator and individual radiators to the light reflection off individual sugar crystals in a glass on the table. Moreover, when our drinks arrived, the reflection of the (blue) saucer in the hot chocolate glass made it appear as if the hot chocolate were layered. In fact it was an optical illusion caused by the way our minds process the colour blue in shadows, more on that in this great article about colour, Goethe and Turner. But it was to a different lighting effect that my thought train eventually turned. Above the counter are a series of hanging lights with angular shades over them. Above our table were LED bulbs inset into the ceiling.

The way that the LEDs above us had been placed produced two shadows from the spoon on the saucer of my cup. A dark shadow and a light shadow at a slightly different angle. One reason that LEDs have caught on as a light source is that they are more efficient and so better environmentally and cheaper financially. So you may think that LEDs are one way of reducing our (collective) environmental footprint. But does this work? According to a study that measured the outdoor light levels around the world from 2012 to 2016, the answer is no. It would appear that while on a local level, people are enjoying cheaper lighting, on larger scales (nationally, globally), this decreased cost is leading to us installing more lights. Consequently, on the global scale, the area of land that is lit has increased by 2.2% per year with very few countries showing a reduction or even a stabilisation of the amount of outdoor areas that are lit.

shadows from a coffee Redemption Roasters

Determining a presence by noticing an absence. The two shadows of the spoon came from the light bulbs inset into the ceiling.

Does this matter? Well, it is something that is affecting us, the way we view our world and the wildlife that we share our planet with and so it is something that we ought to be thinking about. In brightly lit areas of the UK, trees have been shown to produce buds up to 7.5 days earlier than in darker areas. Artificial light is causing problems for nocturnal insects and animals, with knock on effects for crop pollination. And when was the last time you looked up at the sky on a clear night and saw seven of the Pleiades let alone the Milky Way? How does it change our psychology and philosophical outlook when we can no longer gaze at the night sky with wonder and without the glow of streetlights?

Some astronomers have called for increased shielding of street lighting as a way for us to both enjoy well lit streets and be able to enjoy looking up at the night sky. Shielding such as that over the lights over the counter at Redemption Roasters café, where the light is efficiently directed downwards rather than be allowed to escape into the sky. Small steps that can make a big difference. It is interesting to notice that around central London at least, many newer lampposts are more efficiently shielded than older ones. Pausing for a coffee in Redemption Roasters café is a great moment to consider this problem and your reaction to it. Have you stopped to gaze at the night sky recently?

After leaving the café, I realised I had lost an opportunity to notice something else. Frequently, after visiting a good café, I will look up the area in my London Encyclopaedia¹ to see whether there is anything of interest historically in the area of the café. As expected, Lamb’s Conduit St was named after a conduit made from a tributary of the river Fleet restored by one William Lamb in 1577. But Lamb also donated 120 buckets for poor women of the area to use for collecting their water, which explains the statue of a woman with an urn at the top of the street. However what was also mentioned was that at the entrance to Long Yard (ie. very close to Redemption Roasters) there is an ancient stone inset into a wall with a description about the Lamb’s Conduit. Somehow I missed this though Double Skinny Macchiato evidently found it. So if you do visit Redemption Roasters café, and I would very much recommend that you do, as well as taking some time to savour the coffee and to notice the surroundings, please do look out for this elusive stone and if you find it, do let me know.

¹The London Encyclopaedia, Weinreb, Hibbert, Keay and Keay, MacMillan, 2008

Redemption Roasters Cafe is at 84 Lamb’s Conduit St, WC1N 3LR

A cup of tea for a light bulb moment at Ginger and White, Hampstead

Coffee, Ginger and White, Hampstead

Coffee at Ginger and White, Hampstead

It was late afternoon by the time we stopped by Ginger and White in Hampstead. The warm weather meant that we could enjoy time spent sitting outdoors in the little alleyway in front of the café. We had been taking a friend around the various sights (and foodie places) of London and so stopped here before heading back home. The long black, cortado and soya latte were all very well done and, while the others had enjoyed a crepe at La Creperie de Hampstead just around the corner, I took the opportunity to try the excellent banana bread on offer at Ginger and White. There was a fairly good selection of cakes on offer, but sadly those that the staff could confidently affirm were nut free were far fewer. However, the moist and tasty banana bread was a good option anyway. Coffee was roasted by Square Mile and there were also Square Mile beans available for purchase should you wish to take some home with you. While the café was fairly busy, it was nevertheless a relaxing place to sit and watch the people of Hampstead go by.

The interior of Ginger and Whites

Everything is connected. From the lights to your cup of tea.

As I was looking around, wondering what the physics part of this cafe-physics review would be, I had what you could call a “light-bulb moment”. The walls of the building opposite were reflected in the windows of the café but looking inside, I noticed the lights which appeared to be LED lightbulbs set-back into the ceiling. Along with requiring less energy to power than conventional or halogen lightbulbs, LED lightbulbs in a café offer another, more poetic advantage for the café: they have a connection to the drinks being served and particularly tea. It’s all about diffusion.

At the heart of an LED light, there are two materials that form a junction. On one side of the junction is a semiconductor material that conducts electricity by means of electrons. Electrons conduct electricity in metals and are the ‘normal’ way that we consider electrical current to  be carried. On the other side of the junction is a different semiconductor, one that still conducts electricity but this time does so with carriers called ‘holes’. You can view the electrons as having a negative charge and the holes as having a positive charge.

tea bag, tea cup, diffusion, turbulence

What happens when you put a tea bag into a cup of cold water. How long until the water becomes ‘tea’?

But what happens at the junction? Is there really a sharp barrier between these two types of material? Think about putting a tea bag in a cup of cold water, does the tea bag just sit there or does it slowly, very slowly, start to diffuse tea into the cold water? It is a similar thing for the two materials. Slowly the electrons diffuse into the hole material and the holes into the electron material. In fact, mathematically, the same equations describe the process in the junction as in the tea cup. But unlike tea, in the LED, the holes and electrons have an electric charge associated with them and so, as they diffuse away from the junction, they set up an electric field across the junction. It is this electric field that eventually stops any further diffusion of electrons or holes across the junction and sets up the conditions necessary for LEDs to emit light. It would be like having a tea bag that diffuses tea into the cup until it is perfectly brewed and no further.

Of course, there is much more than this to understanding LEDs. If you’re interested, there is further information here. I find it fascinating however that what happens in your tea cup, is also happening on many different scales in many places in the universe. And of course, in the lighting of cafés and coffee houses around the world.

Ginger and Whites is at 4a-5a Perrins Court, NW3 1QS

 

Enlightenment at Timberyard, Seven Dials

coffee, Timberyard, wooden tray

Great coffee at Timberyard

It is not often that you come across an independent café in central London that has great coffee, a good deal of space and seats available and so I found myself very happy to have come across Timberyard near Seven Dials. As I ordered my long black, I was presented with a choice of bean for the espresso base. Should I have the “fruity and acidic” Jabberwocky, or the “chocolate” Climpsons? I was trying Timberyard for the first time and so the choice was easy. For me ‘chocolate’ will win over ‘fruity’ every time. However having the choice was a nice touch. Being in central London, it was of course crowded when I tried it, but there were still seats around, including some stools outside. I took a seat outside, ready to watch the people and the cars going by. After a short while, the coffee was brought over, served on a wooden tray together with a complementary bottle of water.

crema on coffee, Timberyard

The patterns as the crema breaks up are reminiscent of the coastlines of Norway and of fractal mathematics.

It was a very pleasant location to sit and enjoy my coffee while I watched people rushing by on their way to various meetings and tourists milling around, taking their time to soak in the city. As I waited for the coffee to cool, the crema on the surface started to break up and I was reminded of the coastline of Norway. It struck me that the same mathematics of fractals describes the coastlines as would describe the patterns in the crema. It was then that I noticed the street lighting. A light converted from an old style gas lamp was attached to the wall of a shop just across from where I was having my coffee. In the other direction, there was a modern lamp-post of one particular design and then, just slightly further down the road, a lamp-post of a different design. This prompted me to think about the history of street lighting and also the problems with it.

One of the first roads in England to be lit at night was the Route du Roi (nowadays known as Rotten Row) that ran from Kensington Palace to St James Park. Three hundred lamps were hung from trees along the route. These first street lights produced light by burning fuel, a method of street lighting which existed in one form or another until fairly recent times (as evidenced by the oldest street lamp visible from Timberyard). They were installed, as now, to try to reduce crime; it seems that the park used to be frequented by highwaymen. One of these had been hanged for the killing of a woman in the park in 1687. Though it wasn’t quite murder: Rather than be robbed of her wedding ring, the unfortunate lady had attempted to swallow it and so choked to death.

gas lamp, Monmouth St

An old style street lamp on Monmouth St. visible from Timberyard

A more recent type of street light was based on sodium. Applying an electric voltage across a gas of sodium caused the sodium to emit light in the yellow region of the visible spectrum. If rather than sodium, the lights had been based on neon gas, the colour of the light emitted would have been different as the colour corresponds to the different energy levels in the atoms, (for more info click here). In an effort to find increasingly efficient light sources, there is now a move into street lighting based on LEDs (Light emitting diodes). Rather like the sodium lamps, such devices work by applying a voltage over a material but in the case of the LEDs, the material is a semiconductor junction (where the energy gap can be manipulated to have the same size as the energy of visible light). LEDs have the significant advantage that the voltage supplied to produce sufficient lighting can be much less than is the case for sodium lights. This increase in efficiency is a small but effective way to limit our carbon dioxide emissions, especially when used together with sensors on the lamp post to detect when it is dark enough to actually necessitate the light being turned on.

Such a combination of energy saving measures benefits not just the planet but the public wallet. Perhaps in a few years time we’ll see such a set of eco-friendly lamp-posts spring up near Timberyard to add to the collection of street lights there.

In the meanwhile, if you visit Timberyard and notice some interesting physics or history, or if you just slow down and see something interesting, please let me know using the comments box below.

Timberyard is at 7 Upper St Martin’s Lane, Seven Dials, WC2H 9DL (and Old St, EC1V 9HW.)

London info taken from The London Encyclopaedia (3rd Ed), Hibbert et al.